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       gfs2 - GFS2 reference guide


       Overview of the GFS2 filesystem


       GFS2 is a clustered filesystem, designed for sharing data between multiple nodes connected
       to a common shared storage device. It can also be used as a local filesystem on  a  single
       node,  however  since  the  design is aimed at clusters, that will usually result in lower
       performance than using a filesystem designed specifically for single node use.

       GFS2 is a journaling filesystem and one journal is required for each node that will  mount
       the  filesystem.  The  one  exception  to that is spectator mounts which are equivalent to
       mounting a read-only block device and as such can neither recover a journal  or  write  to
       the filesystem, so do not require a journal assigned to them.


              This  specifies  which  inter-node lock protocol is used by the GFS2 filesystem for
              this mount, overriding the default lock protocol name stored  in  the  filesystem's
              on-disk superblock.

              The  LockProtoName  must be one of the supported locking protocols, currently these
              are lock_nolock and lock_dlm.

              The default lock protocol name is written  to  disk  initially  when  creating  the
              filesystem  with  mkfs.gfs2(8),  -p option.  It can be changed on-disk by using the
              gfs2_tool(8) utility's sb proto command.

              The lockproto mount option should be used only under special circumstances in which
              you  want to temporarily use a different lock protocol without changing the on-disk
              default. Using the incorrect lock protocol on a  cluster  filesystem  mounted  from
              more than one node will almost certainly result in filesystem corruption.

              This  specifies  the  identity of the cluster and of the filesystem for this mount,
              overriding the default cluster/filesystem identify stored in the  filesystem's  on-
              disk superblock.  The cluster/filesystem name is recognized globally throughout the
              cluster, and establishes a unique namespace  for  the  inter-node  locking  system,
              enabling the mounting of multiple GFS2 filesystems.

              The  format  of LockTableName is lock-module-specific.  For lock_dlm, the format is
              clustername:fsname.  For lock_nolock, the field is ignored.

              The default cluster/filesystem name is written to disk initially when creating  the
              filesystem  with  mkfs.gfs2(8),  -t option.  It can be changed on-disk by using the
              gfs2_tool(8) utility's sb table command.

              The locktable mount option should be used only under special circumstances in which
              you want to mount the filesystem in a different cluster, or mount it as a different
              filesystem name, without changing the on-disk default.

              This flag tells GFS2 that it is running as a local (not clustered)  filesystem,  so
              it  can  allow  the  kernel VFS layer to do all flock and fcntl file locking.  When
              running in cluster mode, these file locks require inter-node locks, and require the
              support  of  GFS2.  When running locally, better performance is achieved by letting
              VFS handle the whole job.

              This is turned on automatically by the lock_nolock module.

              Setting errors=panic causes GFS2 to oops when  encountering  an  error  that  would
              otherwise  cause  the  mount to withdraw or print an assertion warning. The default
              setting is errors=withdraw. This option should not be used in a production  system.
              It replaces the earlier debug option on kernel versions 2.6.31 and above.

       acl    Enables POSIX Access Control List acl(5) support within GFS2.

              Mount  this filesystem using a special form of read-only mount.  The mount does not
              use one of the filesystem's journals. The node is unable to  recover  journals  for
              other nodes.

              A synonym for spectator

              Sets  owner  of any newly created file or directory to be that of parent directory,
              if parent directory has S_ISUID permission attribute bit set.  Sets S_ISUID in  any
              new directory, if its parent directory's S_ISUID is set.  Strips all execution bits
              on a new file, if parent  directory  owner  is  different  from  owner  of  process
              creating the file.  Set this option only if you know why you are setting it.

              Turns quotas on or off for a filesystem.  Setting the quotas to be in the "account"
              state causes the per UID/GID usage statistics to be  correctly  maintained  by  the
              filesystem, limit and warn values are ignored.  The default value is "off".

              Causes  GFS2  to  generate "discard" I/O requests for blocks which have been freed.
              These can be used by suitable hardware to implement thin-provisioning  and  similar
              schemes. This feature is supported in kernel version 2.6.30 and above.

              This  option,  which defaults to on, causes GFS2 to send I/O barriers when flushing
              the journal. The option is automatically turned off if the underlying  device  does
              not  support I/O barriers. We highly recommend the use of I/O barriers with GFS2 at
              all times unless the block device is designed so that  it  cannot  lose  its  write
              cache content (e.g. its on a UPS, or it doesn't have a write cache)

              This  is  similar  to the ext3 commit= option in that it sets the maximum number of
              seconds between journal commits if there is dirty data in the journal. The  default
              is 60 seconds. This option is only provided in kernel versions 2.6.31 and above.

              When data=ordered is set, the user data modified by a transaction is flushed to the
              disk before the transaction is committed to disk.  This  should  prevent  the  user
              from  seeing  uninitialized  blocks  in  a file after a crash.  Data=writeback mode
              writes the user data to the disk at any time  after  it's  dirtied.   This  doesn't
              provide  the  same consistency guarantee as ordered mode, but it should be slightly
              faster for some workloads.  The default is ordered mode.

       meta   This option results in selecting the meta filesystem root rather  than  the  normal
              filesystem  root.  This option is normally only used by the GFS2 utility functions.
              Altering any file on the GFS2 meta filesystem may render the  filesystem  unusable,
              so only experts in the GFS2 on-disk layout should use this option.

              This sets the number of seconds for which a change in the quota information may sit
              on one node before being written to the quota file. This is the  preferred  way  to
              set  this  parameter.  The value is an integer number of seconds greater than zero.
              The default is 60 seconds. Shorter settings result in faster updates  of  the  lazy
              quota  information  and  less  likelihood  of someone exceeding their quota. Longer
              settings make filesystem operations involving quotas faster and more efficient.

              Setting statfs_quantum to 0 is the preferred way to set the slow version of statfs.
              The  default  value  is  30  secs  which sets the maximum time period before statfs
              changes will be syned to the master statfs file.  This can be adjusted to allow for
              faster,  less accurate statfs values or slower more accurate values. When set to 0,
              statfs will always report the true values.

              This setting provides a bound on  the  maximum  percentage  change  in  the  statfs
              information  on  a  local basis before it is synced back to the master statfs file,
              even if the time period has not expired. If the setting  of  statfs_quantum  is  0,
              then this setting is ignored.


       GFS2  doesn't  support  errors=remount-ro  or  data=journal.  It is not possible to switch
       support for user and group quotas on and off independently of  each  other.  Some  of  the
       error  messages  are  rather cryptic, if you encounter one of these messages check firstly
       that gfs_controld is running and secondly that you have enough journals on the  filesystem
       for the number of nodes in use.


       mount(8)  for  general  mount  options, chmod(1) and chmod(2) for access permission flags,
       acl(5) for access  control  lists,  lvm(8)  for  volume  management,  ccs(7)  for  cluster
       management, umount(8), initrd(4).

       The GFS2 documentation has been split into a number of sections:

       gfs2_edit(8)  A  GFS2  debug  tool  (use  with  caution) fsck.gfs2(8) The GFS2 file system
       checker gfs2_grow(8) Growing a GFS2 file system gfs2_jadd(8) Adding a journal  to  a  GFS2
       file system mkfs.gfs2(8) Make a GFS2 file system gfs2_quota(8) Manipulate GFS2 disk quotas
       gfs2_tool(8) Tool to  manipulate  a  GFS2  file  system  (obsolete)  tunegfs2(8)  Tool  to
       manipulate GFS2 superblocks