sanlock

SANLOCK(8)                  System Manager's Manual                 SANLOCK(8)



NAME
       sanlock - shared storage lock manager


SYNOPSIS
       sanlock [COMMAND] [ACTION] ...


DESCRIPTION
       sanlock is a lock manager built on shared storage.  Hosts with access
       to the storage can perform locking.  An application running on the
       hosts is given a small amount of space on the shared block device or
       file, and uses sanlock for its own application-specific
       synchronization.  Internally, the sanlock daemon manages locks using
       two disk-based lease algorithms: delta leases and paxos leases.


       • delta leases are slow to acquire and demand regular i/o to shared
         storage.  sanlock only uses them internally to hold a lease on its
         "host_id" (an integer host identifier from 1-2000).  They prevent two
         hosts from using the same host identifier.  The delta lease renewals
         also indicate if a host is alive.  ("Light-Weight Leases for Storage-
         Centric Coordination", Chockler and Malkhi.)


       • paxos leases are fast to acquire and sanlock makes them available to
         applications as general purpose resource leases.  The disk paxos
         algorithm uses host_id's internally to represent different hosts, and
         the owner of a paxos lease.  delta leases provide unique host_id's
         for implementing paxos leases, and delta lease renewals serve as a
         proxy for paxos lease renewal.  ("Disk Paxos", Eli Gafni and Leslie
         Lamport.)


       Externally, the sanlock daemon exposes a locking interface through
       libsanlock in terms of "lockspaces" and "resources".  A lockspace is a
       locking context that an application creates for itself on shared
       storage.  When the application on each host is started, it "joins" the
       lockspace.  It can then create "resources" on the shared storage.  Each
       resource represents an application-specific entity.  The application
       can acquire and release leases on resources.

       To use sanlock from an application:


       • Allocate shared storage for an application, e.g. a shared LUN or LV
         from a SAN, or files from NFS.


       • Provide the storage to the application.


       • The application uses this storage with libsanlock to create a
         lockspace and resources for itself.


       • The application joins the lockspace when it starts.


       • The application acquires and releases leases on resources.


       How lockspaces and resources translate to delta leases and paxos leases
       within sanlock:

       Lockspaces


       • A lockspace is based on delta leases held by each host using the
         lockspace.


       • A lockspace is a series of 2000 delta leases on disk, and requires
         1MB of storage.  (See Storage below for size variations.)


       • A lockspace can support up to 2000 concurrent hosts using it, each
         using a different delta lease.


       • Applications can i) create, ii) join and iii) leave a lockspace,
         which corresponds to i) initializing the set of delta leases on disk,
         ii) acquiring one of the delta leases and iii) releasing the delta
         lease.


       • When a lockspace is created, a unique lockspace name and disk
         location is provided by the application.


       • When a lockspace is created/initialized, sanlock formats the sequence
         of 2000 on-disk delta lease structures on the file or disk, e.g.
         /mnt/leasefile (NFS) or /dev/vg/lv (SAN).


       • The 2000 individual delta leases in a lockspace are identified by
         number: 1,2,3,...,2000.


       • Each delta lease is a 512 byte sector in the 1MB lockspace, offset by
         its number, e.g. delta lease 1 is offset 0, delta lease 2 is offset
         512, delta lease 2000 is offset 1023488.  (See Storage below for size
         variations.)


       • When an application joins a lockspace, it must specify the lockspace
         name, the lockspace location on shared disk/file, and the local
         host's host_id.  sanlock then acquires the delta lease corresponding
         to the host_id, e.g. joining the lockspace with host_id 1 acquires
         delta lease 1.


       • The terms delta lease, lockspace lease, and host_id lease are used
         interchangably.


       • sanlock acquires a delta lease by writing the host's unique name to
         the delta lease disk sector, reading it back after a delay, and
         verifying it is the same.


       • If a unique host name is not specified, sanlock generates a uuid to
         use as the host's name.  The delta lease algorithm depends on hosts
         using unique names.


       • The application on each host should be configured with a unique
         host_id, where the host_id is an integer 1-2000.


       • If hosts are misconfigured and have the same host_id, the delta lease
         algorithm is designed to detect this conflict, and only one host will
         be able to acquire the delta lease for that host_id.


       • A delta lease ensures that a lockspace host_id is being used by a
         single host with the unique name specified in the delta lease.


       • Resolving delta lease conflicts is slow, because the algorithm is
         based on waiting and watching for some time for other hosts to write
         to the same delta lease sector.  If multiple hosts try to use the
         same delta lease, the delay is increased substantially.  So, it is
         best to configure applications to use unique host_id's that will not
         conflict.


       • After sanlock acquires a delta lease, the lease must be renewed until
         the application leaves the lockspace (which corresponds to releasing
         the delta lease on the host_id.)


       • sanlock renews delta leases every 20 seconds (by default) by writing
         a new timestamp into the delta lease sector.


       • When a host acquires a delta lease in a lockspace, it can be referred
         to as "joining" the lockspace.  Once it has joined the lockspace, it
         can use resources associated with the lockspace.


       Resources


       • A lockspace is a context for resources that can be locked and
         unlocked by an application.


       • sanlock uses paxos leases to implement leases on resources.  The
         terms paxos lease and resource lease are used interchangably.


       • A paxos lease exists on shared storage and requires 1MB of space.  It
         contains a unique resource name and the name of the lockspace.


       • An application assigns its own meaning to a sanlock resource and the
         leases on it.  A sanlock resource could represent some shared object
         like a file, or some unique role among the hosts.


       • Resource leases are associated with a specific lockspace and can only
         be used by hosts that have joined that lockspace (they are holding a
         delta lease on a host_id in that lockspace.)


       • An application must keep track of the disk locations of its
         lockspaces and resources.  sanlock does not maintain any persistent
         index or directory of lockspaces or resources that have been created
         by applications, so applications need to remember where they have
         placed their own leases (which files or disks and offsets).


       • sanlock does not renew paxos leases directly (although it could).
         Instead, the renewal of a host's delta lease represents the renewal
         of all that host's paxos leases in the associated lockspace. In
         effect, many paxos lease renewals are factored out into one delta
         lease renewal.  This reduces i/o when many paxos leases are used.


       • The disk paxos algorithm allows multiple hosts to all attempt to
         acquire the same paxos lease at once, and will produce a single
         winner/owner of the resource lease.  (Shared resource leases are also
         possible in addition to the default exclusive leases.)


       • The disk paxos algorithm involves a specific sequence of reading and
         writing the sectors of the paxos lease disk area.  Each host has a
         dedicated 512 byte sector in the paxos lease disk area where it
         writes its own "ballot", and each host reads the entire disk area to
         see the ballots of other hosts.  The first sector of the disk area is
         the "leader record" that holds the result of the last paxos ballot.
         The winner of the paxos ballot writes the result of the ballot to the
         leader record (the winner of the ballot may have selected another
         contending host as the owner of the paxos lease.)


       • After a paxos lease is acquired, no further i/o is done in the paxos
         lease disk area.


       • Releasing the paxos lease involves writing a single sector to clear
         the current owner in the leader record.


       • If a host holding a paxos lease fails, the disk area of the paxos
         lease still indicates that the paxos lease is owned by the failed
         host.  If another host attempts to acquire the paxos lease, and finds
         the lease is held by another host_id, it will check the delta lease
         of that host_id.  If the delta lease of the host_id is being renewed,
         then the paxos lease is owned and cannot be acquired.  If the delta
         lease of the owner's host_id has expired, then the paxos lease is
         expired and can be taken (by going through the paxos lease
         algorithm.)


       • The "interaction" or "awareness" between hosts of each other is
         limited to the case where they attempt to acquire the same paxos
         lease, and need to check if the referenced delta lease has expired or
         not.


       • When hosts do not attempt to lock the same resources concurrently,
         there is no host interaction or awareness.  The state or actions of
         one host have no effect on others.


       • To speed up checking delta lease expiration (in the case of a paxos
         lease conflict), sanlock keeps track of past renewals of other delta
         leases in the lockspace.


       Resource Index

       The resource index (rindex) is an optional sanlock feature that
       applications can use to keep track of resource lease offsets.  Without
       the rindex, an application must keep track of where its resource leases
       exist on disk and find available locations when creating new leases.

       The sanlock rindex uses two align-size areas on disk following the
       lockspace.  The first area holds rindex entries; each entry records a
       resource lease name and location.  The second area holds a private
       paxos lease, used by sanlock internally to protect rindex updates.

       The application creates the rindex on disk with the "format" function.
       Format is a disk-only operation and does not interact with the live
       lockspace, so it can be called without first calling add_lockspace.
       The application needs to follow the convention of writing the lockspace
       at the start of the device (offset 0) and formatting the rindex
       immediately following the lockspace area.  When formatting, the
       application must set flags for sector size and align size to match
       those for the lockspace.

       To use the rindex, the application:


       • Uses the "create" function to create a new resource lease on disk.
         This takes the place of the write_resource function.  The create
         function requires the location of the rindex and the name of the new
         resource lease.  sanlock finds a free lease area, writes the new
         resource lease at that location, updates the rindex with the
         name:offset, and returns the offset to the caller.  The caller uses
         this offset when acquiring the resource lease.


       • Uses the "delete" function to remove a resource disk on disk (also
         corresponding to the write_resource function.)  sanlock clears the
         resource lease and the rindex entry for it.  A subsequent call to
         create may use this same disk location for a different resource
         lease.


       • Uses the "lookup" function to discover the offset of a resource lease
         given the resource lease name.  The caller would typically call this
         prior to acquiring the resource lease.


       • Uses the "rebuild" function to recreate the rindex if it is damaged
         or becomes inconsistent.  This function scans the disk for resource
         leases and creates new rindex entries to match the leases it finds.


       • The "update" function manipulates rindex entries directly and should
         not normally be used by the application.  In normal usage, the create
         and delete functions manipulate rindex entries.  Update is mainly
         useful for testing or repairs.


       Expiration


       • If a host fails to renew its delta lease, e.g. it looses access to
         the storage, its delta lease will eventually expire and another host
         will be able to take over any resource leases held by the host.
         sanlock must ensure that the application on two different hosts is
         not holding and using the same lease concurrently.


       • When sanlock has failed to renew a delta lease for a period of time,
         it will begin taking measures to stop local processes (applications)
         from using any resource leases associated with the expiring lockspace
         delta lease.  sanlock enters this "recovery mode" well ahead of the
         time when another host could take over the locally owned leases.
         sanlock must have sufficient time to stop all local processes that
         are using the expiring leases.


       • sanlock uses three methods to stop local processes that are using
         expiring leases:

         1. Graceful shutdown.  sanlock will execute a "graceful shutdown"
         program that the application previously specified for this case.  The
         shutdown program tells the application to shut down because its
         leases are expiring.  The application must respond by stopping its
         activities and releasing its leases (or exit).  If an application
         does not specify a graceful shutdown program, sanlock sends SIGTERM
         to the process instead.  The process must release its leases or exit
         in a prescribed amount of time (see -g), or sanlock proceeds to the
         next method of stopping.

         2. Forced shutdown.  sanlock will send SIGKILL to processes using the
         expiring leases.  The processes have a fixed amount of time to exit
         after receiving SIGKILL.  If any do not exit in this time, sanlock
         will proceed to the next method.

         3. Host reset.  sanlock will trigger the host's watchdog device to
         forcibly reset it.  sanlock carefully manages the timing of the
         watchdog device so that it fires shortly before any other host could
         take over the resource leases held by local processes.


       Failures

       If a process holding resource leases fails or exits without releasing
       its leases, sanlock will release the leases for it automatically
       (unless persistent resource leases were used.)

       If the sanlock daemon cannot renew a lockspace delta lease for a
       specific period of time (see Expiration), sanlock will enter "recovery
       mode" where it attempts to stop and/or kill any processes holding
       resource leases in the expiring lockspace.  If the processes do not
       exit in time, sanlock will force the host to be reset using the local
       watchdog device.

       If the sanlock daemon crashes or hangs, it will not renew the expiry
       time of the per-lockspace connections it had to the wdmd daemon.  This
       will lead to the expiration of the local watchdog device, and the host
       will be reset.

       Watchdog

       sanlock uses the wdmd(8) daemon to access /dev/watchdog.  wdmd
       multiplexes multiple timeouts onto the single watchdog timer.  This is
       required because delta leases for each lockspace are renewed and expire
       independently.

       sanlock maintains a wdmd connection for each lockspace delta lease
       being renewed.  Each connection has an expiry time for some seconds in
       the future.  After each successful delta lease renewal, the expiry time
       is renewed for the associated wdmd connection.  If wdmd finds any
       connection expired, it will not renew the /dev/watchdog timer.  Given
       enough successive failed renewals, the watchdog device will fire and
       reset the host.  (Given the multiplexing nature of wdmd, shorter
       overlapping renewal failures from multiple lockspaces could cause
       spurious watchdog firing.)

       The direct link between delta lease renewals and watchdog renewals
       provides a predictable watchdog firing time based on delta lease
       renewal timestamps that are visible from other hosts.  sanlock knows
       the time the watchdog on another host has fired based on the delta
       lease time.  Furthermore, if the watchdog device on another host fails
       to fire when it should, the continuation of delta lease renewals from
       the other host will make this evident and prevent leases from being
       taken from the failed host.

       If sanlock is able to stop/kill all processing using an expiring
       lockspace, the associated wdmd connection for that lockspace is
       removed.  The expired wdmd connection will no longer block
       /dev/watchdog renewals, and the host should avoid being reset.

       Storage

       The sector size and the align size should be specified when creating
       lockspaces and resources (and rindex).  The "align size" is the size on
       disk of a lockspace or a resource, i.e. the amount of disk space it
       uses.  Lockspaces and resources should use matching sector and align
       sizes, and must use offsets in multiples of the align size.  The max
       number of hosts that can use a lockspace or resource depends on the
       combination of sector size and align size, shown below.  The host_id of
       hosts using the lockspace can be no larger than the max_hosts value for
       the lockspace.

       Accepted combinations of sector size and align size, and the
       corresponding max_hosts (and max host_id) are:

       sector_size 512, align_size 1M, max_hosts 2000
       sector_size 4096, align_size 1M, max_hosts 250
       sector_size 4096, align_size 2M, max_hosts 500
       sector_size 4096, align_size 4M, max_hosts 1000
       sector_size 4096, align_size 8M, max_hosts 2000

       When sector_size and align_size are not specified, the behavior matches
       the behavior before these sizes could be configured: on devices which
       report sector size 512, 512/1M/2000 is used, on devices which report
       sector size 4096, 4096/8M/2000 is used, and on files, 512/1M/2000 is
       always used.  (Other combinations are not compatible with sanlock
       version 3.6 or earlier.)

       Using sanlock on shared block devices that do host based mirroring or
       replication is not likely to work correctly.  When using sanlock on
       shared files, all sanlock io should go to one file server.

       Example

       This is an example of creating and using lockspaces and resources from
       the command line.  (Most applications would use sanlock through
       libsanlock rather than through the command line.)


       1.  Allocate shared storage for sanlock leases.

           This example assumes 512 byte sectors on the device, in which case
           the lockspace needs 1MB and each resource needs 1MB.

           The example shared block device accessible to all hosts is
           /dev/leases.


       2.  Start sanlock on all hosts.

           The -w 0 disables use of the watchdog for testing.

           # sanlock daemon -w 0


       3.  Start a dummy application on all hosts.

           This sanlock command registers with sanlock, then execs the sleep
           command which inherits the registered fd.  The sleep process acts
           as the dummy application.  Because the sleep process is registered
           with sanlock, leases can be acquired for it.

           # sanlock client command -c /bin/sleep 600 &


       4.  Create a lockspace for the application (from one host).

           The lockspace is named "test".

           # sanlock client init -s test:0:/dev/leases:0


       5.  Join the lockspace for the application.

           Use a unique host_id on each host.

           host1:
           # sanlock client add_lockspace -s test:1:/dev/leases:0
           host2:
           # sanlock client add_lockspace -s test:2:/dev/leases:0


       6.  Create two resources for the application (from one host).

           The resources are named "RA" and "RB".  Offsets are used on the
           same device as the lockspace.  Different LVs or files could also be
           used.

           # sanlock client init -r test:RA:/dev/leases:1048576
           # sanlock client init -r test:RB:/dev/leases:2097152


       7.  Acquire resource leases for the application on host1.

           Acquire an exclusive lease (the default) on the first resource, and
           a shared lease (SH) on the second resource.

           # export P=`pidof sleep`
           # sanlock client acquire -r test:RA:/dev/leases:1048576 -p $P
           # sanlock client acquire -r test:RB:/dev/leases:2097152:SH -p $P


       8.  Acquire resource leases for the application on host2.

           Acquiring the exclusive lease on the first resource will fail
           because it is held by host1.  Acquiring the shared lease on the
           second resource will succeed.

           # export P=`pidof sleep`
           # sanlock client acquire -r test:RA:/dev/leases:1048576 -p $P
           # sanlock client acquire -r test:RB:/dev/leases:2097152:SH -p $P


       9.  Release resource leases for the application on both hosts.

           The sleep pid could also be killed, which will result in the
           sanlock daemon releasing its leases when it exits.

           # sanlock client release -r test:RA:/dev/leases:1048576 -p $P
           # sanlock client release -r test:RB:/dev/leases:2097152 -p $P


       10. Leave the lockspace for the application.

           host1:
           # sanlock client rem_lockspace -s test:1:/dev/leases:0
           host2:
           # sanlock client rem_lockspace -s test:2:/dev/leases:0


       11. Stop sanlock on all hosts.

           # sanlock shutdown



OPTIONS
       COMMAND can be one of three primary top level choices

       sanlock daemon start daemon
       sanlock client send request to daemon (default command if none given)
       sanlock direct access storage directly (no coordination with daemon)


   Daemon Command
       sanlock daemon [options]

       -D no fork and print all logging to stderr

       -Q 0|1 quiet error messages for common lock contention

       -R 0|1 renewal debugging, log debug info for each renewal

       -L pri write logging at priority level and up to logfile (-1 none)

       -S pri write logging at priority level and up to syslog (-1 none)

       -U uid user id

       -G gid group id

       -H num renewal history size

       -t num max worker threads

       -g sec seconds for graceful recovery

       -w 0|1 use watchdog through wdmd

       -h 0|1 use high priority (RR) scheduling

       -l num use mlockall (0 none, 1 current, 2 current and future)

       -b sec seconds a host id bit will remain set in delta lease bitmap

       -e str local host name used in delta leases



   Client Command
       sanlock client action [options]

       sanlock client status

       Print processes, lockspaces, and resources being managed by the sanlock
       daemon.  Add -D to show extra internal daemon status for debugging.
       Add -o p to show resources by pid, or -o s to show resources by
       lockspace.

       sanlock client host_status

       Print state of host_id delta leases read during the last renewal.
       State of all lockspaces is shown (use -s to select one).  Add -D to
       show extra internal daemon status for debugging.

       sanlock client gets

       Print lockspaces being managed by the sanlock daemon.  The LOCKSPACE
       string will be followed by ADD or REM if the lockspace is currently
       being added or removed.  Add -h 1 to also show hosts in each lockspace.

       sanlock client renewal -s LOCKSPACE

       Print a history of renewals with timing details.  See the Renewal
       history section below.

       sanlock client log_dump

       Print the sanlock daemon internal debug log.

       sanlock client shutdown

       Ask the sanlock daemon to exit.  Without the force option (-f 0), the
       command will be ignored if any lockspaces exist.  With the force option
       (-f 1), any registered processes will be killed, their resource leases
       released, and lockspaces removed.  With the wait option (-w 1), the
       command will wait for a result from the daemon indicating that it has
       shut down and is exiting, or cannot shut down because lockspaces exist
       (command fails).

       sanlock client init -s LOCKSPACE

       Tell the sanlock daemon to initialize a lockspace on disk.  The -o
       option can be used to specify the io timeout to be written in the
       host_id leases.  The -Z and -A options can be used to specify the
       sector size and align size, and both should be set together.  (Also see
       sanlock direct init.)

       sanlock client init -r RESOURCE

       Tell the sanlock daemon to initialize a resource lease on disk.  The -Z
       and -A options can be used to specify the sector size and align size,
       and both should be set together.  (Also see sanlock direct init.)

       sanlock client read -s LOCKSPACE

       Tell the sanlock daemon to read a lockspace from disk.  Only the
       LOCKSPACE path and offset are required.  If host_id is zero, the first
       record at offset (host_id 1) is used.  The complete LOCKSPACE is
       printed.  Add -D to print other details.  (Also see sanlock direct
       read_leader.)

       sanlock client read -r RESOURCE

       Tell the sanlock daemon to read a resource lease from disk.  Only the
       RESOURCE path and offset are required.  The complete RESOURCE is
       printed.  Add -D to print other details.  (Also see sanlock direct
       read_leader.)

       sanlock client add_lockspace -s LOCKSPACE

       Tell the sanlock daemon to acquire the specified host_id in the
       lockspace.  This will allow resources to be acquired in the lockspace.
       The -o option can be used to specify the io timeout of the acquiring
       host, and will be written in the host_id lease.

       sanlock client inq_lockspace -s LOCKSPACE

       Inquire about the state of the lockspace in the sanlock daemon, whether
       it is being added or removed, or is joined.

       sanlock client rem_lockspace -s LOCKSPACE

       Tell the sanlock daemon to release the specified host_id in the
       lockspace.  Any processes holding resource leases in this lockspace
       will be killed, and the resource leases not released.

       sanlock client command -r RESOURCE -c path args

       Register with the sanlock daemon, acquire the specified resource lease,
       and exec the command at path with args.  When the command exits, the
       sanlock daemon will release the lease.  -c must be the final option.

       sanlock client acquire -r RESOURCE -p pid
       sanlock client release -r RESOURCE -p pid

       Tell the sanlock daemon to acquire or release the specified resource
       lease for the given pid.  The pid must be registered with the sanlock
       daemon.  acquire can optionally take a versioned RESOURCE string
       RESOURCE:lver, where lver is the version of the lease that must be
       acquired, or fail.

       sanlock client convert -r RESOURCE -p pid

       Tell the sanlock daemon to convert the mode of the specified resource
       lease for the given pid.  If the existing mode is exclusive (default),
       the mode of the lease can be converted to shared with RESOURCE:SH.  If
       the existing mode is shared, the mode of the lease can be converted to
       exclusive with RESOURCE (no :SH suffix).

       sanlock client inquire -p pid

       Print the resource leases held the given pid.  The format is a
       versioned RESOURCE string "RESOURCE:lver" where lver is the version of
       the lease held.

       sanlock client request -r RESOURCE -f force_mode

       Request the owner of a resource do something specified by force_mode.
       A versioned RESOURCE:lver string must be used with a greater version
       than is presently held.  Zero lver and force_mode clears the request.

       sanlock client examine -r RESOURCE

       Examine the request record for the currently held resource lease and
       carry out the action specified by the requested force_mode.

       sanlock client examine -s LOCKSPACE

       Examine requests for all resource leases currently held in the named
       lockspace.  Only lockspace_name is used from the LOCKSPACE argument.

       sanlock client set_event -s LOCKSPACE -i host_id -g gen -e num -d num

       Set an event for another host.  When the sanlock daemon next renews its
       delta lease for the lockspace it will: set the bit for the host_id in
       its bitmap, and set the generation, event and data values in its own
       delta lease.  An application that has registered for events from this
       lockspace on the destination host will get the event that has been set
       when the destination sees the event during its next delta lease
       renewal.

       sanlock client set_config -s LOCKSPACE

       Set a configuration value for a lockspace.  Only lockspace_name is used
       from the LOCKSPACE argument.  The USED flag has the same effect on a
       lockspace as a process holding a resource lease that will not exit.
       The USED_BY_ORPHANS flag means that an orphan resource lease will have
       the same effect as the USED.
       -u 0|1 Set (1) or clear (0) the USED flag.
       -O 0|1 Set (1) or clear (0) the USED_BY_ORPHANS flag.

       sanlock client format -x RINDEX

       Create a resource index on disk.  Use -Z and -A to set the sector size
       and align size to match the lockspace.

       sanlock client create -x RINDEX -e resource_name

       Create a new resource lease on disk, using the rindex to find a free
       offset.

       sanlock client delete -x RINDEX -e resource_name[:offset]

       Delete an existing resource lease on disk.

       sanlock client lookup -x RINDEX -e resource_name

       Look up the offset of an existing resource lease by name on disk, using
       the rindex.  With no -e option, lookup returns the next free lease
       offset.  If -e specifes both name and offset, the lookup verifies both
       are correct.

       sanlock client update -x RINDEX -e resource_name[:offset] [-z 0|1]

       Add (-z 0) or remove (-z 1) an rindex entry on disk.

       sanlock client rebuild -x RINDEX

       Rebuild the rindex entries by scanning the disk for resource leases.



   Direct Command
       sanlock direct action [options]


       -o sec io timeout in seconds

       sanlock direct init -s LOCKSPACE
       sanlock direct init -r RESOURCE

       Initialize storage for a lockspace or resource.  Use the -Z and -A
       flags to specify the sector size and align size.  The max hosts that
       can use the lockspace/resource (and the max possible host_id) is
       determined by the sector/align size combination.  Possible combinations
       are: 512/1M, 4096/1M, 4096/2M, 4096/4M, 4096/8M.  Lockspaces and
       resources both use the same amount of space (align_size) for each
       combination.  When initializing a lockspace, sanlock initializes delta
       leases for max_hosts in the given space.  When initializing a resource,
       sanlock initializes a single paxos lease in the space.  With -s, the -o
       option specifies the io timeout to be written in the host_id leases.
       With -r, the -z 1 option invalidates the resource lease on disk so it
       cannot be used until reinitialized normally.

       sanlock direct read_leader -s LOCKSPACE
       sanlock direct read_leader -r RESOURCE

       Read a leader record from disk and print the fields.  The leader record
       is the single sector of a delta lease, or the first sector of a paxos
       lease.

       sanlock direct dump path[:offset[:size]]

       Read disk sectors and print leader records for delta or paxos leases.
       Add -f 1 to print the request record values for paxos leases, host_ids
       set in delta lease bitmaps, and rindex entries.

       sanlock direct format -x RINDEX
       sanlock direct lookup -x RINDEX -e resource_name
       sanlock direct update -x RINDEX -e resource_name[:offset] [-z 0|1]
       sanlock direct rebuild -x RINDEX

       Access the resource index on disk without going through the sanlock
       daemon.  This precludes using the internal paxos lease to protect
       rindex modifications.  See client equivalents for descriptions.



   LOCKSPACE option string
       -s lockspace_name:host_id:path:offset

       lockspace_name name of lockspace
       host_id local host identifier in lockspace
       path path to storage to use for leases
       offset offset on path (bytes)


   RESOURCE option string
       -r lockspace_name:resource_name:path:offset

       lockspace_name name of lockspace
       resource_name name of resource
       path path to storage to use leases
       offset offset on path (bytes)


   RESOURCE option string with suffix
       -r lockspace_name:resource_name:path:offset:lver

       lver leader version

       -r lockspace_name:resource_name:path:offset:SH

       SH indicates shared mode


   RINDEX option string
       -x lockspace_name:path:offset

       lockspace_name name of lockspace
       path path to storage to use for leases
       offset offset on path (bytes) of rindex



   Defaults
       sanlock help shows the default values for the options above.

       sanlock version shows the build version.


OTHER
   Request/Examine
       The first part of making a request for a resource is writing the
       request record of the resource (the sector following the leader
       record).  To make a successful request:

       • RESOURCE:lver must be greater than the lver presently held by the
         other host.  This implies the leader record must be read to discover
         the lver, prior to making a request.

       • RESOURCE:lver must be greater than or equal to the lver presently
         written to the request record.  Two hosts may write a new request at
         the same time for the same lver, in which case both would succeed,
         but the force_mode from the last would win.

       • The force_mode must be greater than zero.

       • To unconditionally clear the request record (set both lver and
         force_mode to 0), make request with RESOURCE:0 and force_mode 0.


       The owner of the requested resource will not know of the request unless
       it is explicitly told to examine its resources via the "examine"
       api/command, or otherwise notfied.

       The second part of making a request is notifying the resource lease
       owner that it should examine the request records of its resource
       leases.  The notification will cause the lease owner to automatically
       run the equivalent of "sanlock client examine -s LOCKSPACE" for the
       lockspace of the requested resource.

       The notification is made using a bitmap in each host_id delta lease.
       Each bit represents each of the possible host_ids (1-2000).  If host A
       wants to notify host B to examine its resources, A sets the bit in its
       own bitmap that corresponds to the host_id of B.  When B next renews
       its delta lease, it reads the delta leases for all hosts and checks
       each bitmap to see if its own host_id has been set.  It finds the bit
       for its own host_id set in A's bitmap, and examines its resource
       request records.  (The bit remains set in A's bitmap for
       set_bitmap_seconds.)

       force_mode determines the action the resource lease owner should take:


       • FORCE (1): kill the process holding the resource lease.  When the
         process has exited, the resource lease will be released, and can then
         be acquired by anyone.  The kill signal is SIGKILL (or SIGTERM if
         SIGKILL is restricted.)


       • GRACEFUL (2): run the program configured by sanlock_killpath against
         the process holding the resource lease.  If no killpath is defined,
         then FORCE is used.


   Persistent and orphan resource leases
       A resource lease can be acquired with the PERSISTENT flag (-P 1).  If
       the process holding the lease exits, the lease will not be released,
       but kept on an orphan list.  Another local process can acquire an
       orphan lease using the ORPHAN flag (-O 1), or release the orphan lease
       using the ORPHAN flag (-O 1).  All orphan leases can be released by
       setting the lockspace name (-s lockspace_name) with no resource name.


   Renewal history
       sanlock saves a limited history of lease renewal information in each
       lockspace.  See sanlock.conf renewal_history_size to set the amount of
       history or to disable (set to 0).

       IO times are measured in delta lease renewal (each delta lease renewal
       includes one read and one write).

       For each successful renewal, a record is saved that includes:

       • the timestamp written in the delta lease by the renewal

       • the time in milliseconds taken by the delta lease read

       • the time in milliseconds taken by the delta lease write


       Also counted and recorded are the number io timeouts and other io
       errors that occur between successful renewals.

       Two consecutive successful renewals would be recorded as:
       timestamp=5332 read_ms=482 write_ms=5525 next_timeouts=0 next_errors=0
       timestamp=5353 read_ms=99 write_ms=3161 next_timeouts=0 next_errors=0

       Those fields are:


       • timestamp is the value written into the delta lease during that
         renewal.


       • read_ms/write_ms are the milliseconds taken for the renewal
         read/write ios.


       • next_timeouts are the number of io timeouts that occured after the
         renewal recorded on that line, and before the next successful renewal
         on the following line.


       • next_errors are the number of io errors (not timeouts) that occured
         after renewal recorded on that line, and before the next successful
         renewal on the following line.


       The command 'sanlock client renewal -s lockspace_name' reports the full
       history of renewals saved by sanlock, which by default is 180 records,
       about 1 hour of history when using a 20 second renewal interval for a
       10 second io timeout.


INTERNALS
   Disk Format
       • This example uses 512 byte sectors.

       • Each lockspace is 1MB.  It holds 2000 delta_leases, one per sector,
         supporting up to 2000 hosts.

       • Each paxos_lease is 1MB.  It is used as a lease for one resource.

       • The leader_record structure is used differently by each lease type.

       • To display all leader_record fields, see sanlock direct read_leader.

       • A lockspace is often followed on disk by the paxos_leases used within
         that lockspace, but this layout is not required.

       • The request_record and host_id bitmap are used for requests/events.

       • The mode_block contains the SHARED flag indicating a lease is held in
         the shared mode.

       • In a lockspace, the host using host_id N writes to a single
         delta_lease in sector N-1.  No other hosts write to this sector.  All
         hosts read all lockspace sectors when renewing their own delta_lease,
         and are able to monitor renewals of all delta_leases.

       • In a paxos_lease, each host has a dedicated sector it writes to,
         containing its own paxos_dblock and mode_block structures.  Its
         sector is based on its host_id; host_id 1 writes to the
         dblock/mode_block in sector 2 of the paxos_lease.

       • The paxos_dblock structures are used by the paxos_lease algorithm,
         and the result is written to the leader_record.


       0x000000 lockspace foo:0:/path:0

       (There is no representation on disk of the lockspace in general, only
       the sequence of specific delta_leases which collectively represent the
       lockspace.)

       delta_lease foo:1:/path:0
       0x000 0         leader_record         (sector 0, for host_id 1)
                       magic: 0x12212010
                       space_name: foo
                       resource_name: host uuid/name
                       ...
                       host_id bitmap        (leader_record + 256)

       delta_lease foo:2:/path:0
       0x200 512       leader_record         (sector 1, for host_id 2)
                       magic: 0x12212010
                       space_name: foo
                       resource_name: host uuid/name
                       ...
                       host_id bitmap        (leader_record + 256)

       delta_lease foo:3:/path:0
       0x400 1024      leader_record         (sector 2, for host_id 3)
                       magic: 0x12212010
                       space_name: foo
                       resource_name: host uuid/name
                       ...
                       host_id bitmap        (leader_record + 256)

       delta_lease foo:2000:/path:0
       0xF9E00         leader_record         (sector 1999, for host_id 2000)
                       magic: 0x12212010
                       space_name: foo
                       resource_name: host uuid/name
                       ...
                       host_id bitmap        (leader_record + 256)

       0x100000 paxos_lease foo:example1:/path:1048576
       0x000 0         leader_record         (sector 0)
                       magic: 0x06152010
                       space_name: foo
                       resource_name: example1

       0x200 512       request_record        (sector 1)
                       magic: 0x08292011

       0x400 1024      paxos_dblock          (sector 2, for host_id 1)
       0x480 1152      mode_block            (paxos_dblock + 128)

       0x600 1536      paxos_dblock          (sector 3, for host_id 2)
       0x680 1664      mode_block            (paxos_dblock + 128)

       0x800 2048      paxos_dblock          (sector 4, for host_id 3)
       0x880 2176      mode_block            (paxos_dblock + 128)

       0xFA200         paxos_dblock          (sector 2001, for host_id 2000)
       0xFA280         mode_block            (paxos_dblock + 128)

       0x200000 paxos_lease foo:example2:/path:2097152
       0x000 0         leader_record         (sector 0)
                       magic: 0x06152010
                       space_name: foo
                       resource_name: example2

       0x200 512       request_record        (sector 1)
                       magic: 0x08292011

       0x400 1024      paxos_dblock          (sector 2, for host_id 1)
       0x480 1152      mode_block            (paxos_dblock + 128)

       0x600 1536      paxos_dblock          (sector 3, for host_id 2)
       0x680 1664      mode_block            (paxos_dblock + 128)

       0x800 2048      paxos_dblock          (sector 4, for host_id 3)
       0x880 2176      mode_block            (paxos_dblock + 128)

       0xFA200         paxos_dblock          (sector 2001, for host_id 2000)
       0xFA280         mode_block            (paxos_dblock + 128)


   Lease ownership
       Not shown in the leader_record structures above are the owner_id,
       owner_generation and timestamp fields.  These are the fields that
       define the lease owner.

       The delta_lease at sector N for host_id N+1 has leader_record.owner_id
       N+1.  The leader_record.owner_generation is incremented each time the
       delta_lease is acquired.  When a delta_lease is acquired, the
       leader_record.timestamp field is set to the time of the host and the
       leader_record.resource_name is set to the unique name of the host.
       When the host renews the delta_lease, it writes a new
       leader_record.timestamp.  When a host releases a delta_lease, it writes
       zero to leader_record.timestamp.

       When a host acquires a paxos_lease, it uses the host_id/generation
       value from the delta_lease it holds in the lockspace.  It uses this
       host_id/generation to identify itself in the paxos_dblock when running
       the paxos algorithm.  The result of the algorithm is the winning
       host_id/generation - the new owner of the paxos_lease.  The winning
       host_id/generation are written to the paxos_lease
       leader_record.owner_id and leader_record.owner_generation fields and
       leader_record.timestamp is set.  When a host releases a paxos_lease, it
       sets leader_record.timestamp to 0.

       When a paxos_lease is free (leader_record.timestamp is 0), multiple
       hosts may attempt to acquire it.  The paxos algorithm, using the
       paxos_dblock structures, will select only one of the hosts as the new
       owner, and that owner is written in the leader_record.  The paxos_lease
       will no longer be free (non-zero timestamp).  Other hosts will see this
       and will not attempt to acquire the paxos_lease until it is free again.

       If a paxos_lease is owned (non-zero timestamp), but the owner has not
       renewed its delta_lease for a specific length of time, then the owner
       value in the paxos_lease becomes expired, and other hosts will use the
       paxos algorithm to acquire the paxos_lease, and set a new owner.


FILES
       /etc/sanlock/sanlock.conf


       • quiet_fail = 1
         See -Q


       • debug_renew = 0
         See -R


       • logfile_priority = 4
         See -L


       • logfile_use_utc = 0
         Use UTC instead of local time in log messages.


       • syslog_priority = 3
         See -S


       • names_log_priority = 4
         Log resource names at this priority level (uses syslog priority
         numbers).  If this is greater than or equal to logfile_priority, each
         requested resource name and location is recorded in sanlock.log.


       • use_watchdog = 1
         See -w


       • high_priority = 1
         See -h


       • mlock_level = 1
         See -l


       • sh_retries = 8
         The number of times to try acquiring a paxos lease when acquiring a
         shared lease when the paxos lease is held by another host acquiring a
         shared lease.


       • uname = sanlock
         See -U


       • gname = sanlock
         See -G


       • our_host_name = <str>
         See -e


       • renewal_read_extend_sec = <seconds>
         If a renewal read i/o times out, wait this many additional seconds
         for that read to complete at the start of the subsequent renewal
         attempt.  When not configured, sanlock waits for an additional
         io_timeout seconds for a previous timed out read to complete.


       • renewal_history_size = 180
         See -H


       • paxos_debug_all = 0
         Include all details in the paxos debug logging.


       • debug_io = <str>
         Add debug logging for each i/o.  "submit" (no quotes) produces debug
         output at submission time, "complete" produces debug output at
         completion time, and "submit,complete" (no space) produces both.


       • max_sectors_kb = <str>|<num>
         Set to "ignore" (no quotes) to prevent sanlock from checking or
         changing max_sectors_kb for the lockspace disk when starting a
         lockspace.  Set to "align" (no quotes) to set max_sectors_kb for the
         lockspace disk to the align size of the lockspace.  Set to a number
         to set a specific number of KB for all lockspace disks.


       • debug_clients = 0
         Enable or disable debug logging for all client connections to the
         sanlock daemon.


       • debug_cmd = +|-<name>
         Enable (+name) or disable (-name) debug logging at the command
         processing level for specifically named commands, e.g. "debug_cmd =
         +acquire", or "debug_cmd = -inq_lockspace".  Repeat this line for
         each command name.  Use a plus prefix before the name to enable and a
         minus prefix to disable.  By default sanlock disables some command
         level debugging for commands that are often repetitive and fill the
         in memory debug buffer.  This only affects debug logging, not errors
         or warnings, and disabling command level debugging for a command does
         not disable lower level debugging for that command.  Special values
         +all and -all can be used to enable or disable all commands, and can
         be used before or after other debug_cmd lines.


SEE ALSO
       wdmd(8)




                                  2015-01-23                        SANLOCK(8)