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GJOURNAL(8)		  BSD System Manager's Manual		   GJOURNAL(8)

NAME
     gjournal — control utility for journaled devices

SYNOPSIS
     gjournal label [-cfhv] [-s jsize] dataprov [jprov]
     gjournal stop [-fv] name ...
     gjournal sync [-v]
     gjournal clear [-v] prov ...
     gjournal dump prov ...
     gjournal list
     gjournal status
     gjournal load
     gjournal unload

DESCRIPTION
     The gjournal utility is used for journal configuration on the given GEOM
     provider.	The Journal and data may be stored on the same provider or on
     two separate providers.  This is block level journaling, not file system
     level journaling, which means everything gets logged, e.g. for file sys‐
     tems, it journals both data and metadata.	The gjournal GEOM class can
     talk to file systems, which allows the use of gjournal for file system
     journaling and to keep file systems in a consistent state.	 At this time,
     only UFS file system is supported.

     To configure journaling on the UFS file system using gjournal, one should
     first create a gjournal provider using the gjournal utility, then run
     newfs(8) or tunefs(8) on it with the -J flag which instructs UFS to coop‐
     erate with the gjournal provider below.  There are important differences
     in how journaled UFS works.  The most important one is that sync(2) and
     fsync(2) system calls do not work as expected anymore.  To ensure that
     data is stored on the data provider, the gjournal sync command should be
     used after calling sync(2).  For the best performance possible, soft-
     updates should be disabled when gjournal is used.	It is also safe and
     recommended to use the async mount(8) option.

     When gjournal is configured on top of gmirror(8) or graid3(8) providers,
     it also keeps them in a consistent state, thus automatic synchronization
     on power failure or system crash may be disabled on those providers.

     The gjournal utility uses on-disk metadata, stored in the provider's last
     sector, to store all needed information.  This could be a problem when an
     existing file system is converted to use gjournal.

     The first argument to gjournal indicates an action to be performed:

     label   Configures gjournal on the given provider(s).  If only one
	     provider is given, both data and journal are stored on the same
	     provider.	If two providers are given, the first one will be used
	     as data provider and the second will be used as the journal
	     provider.

	     Additional options include:

	     -c	       Checksum journal records.

	     -f	       May be used to convert an existing file system to use
		       gjournal, but only if the journal will be configured on
		       a separate provider and if the last sector in the data
		       provider is not used by the existing file system.  If
		       gjournal detects that the last sector is used, it will
		       refuse to overwrite it and return an error.  This
		       behavior may be forced by using the -f flag, which will
		       force gjournal to overwrite the last sector.

	     -h	       Hardcode provider names in metadata.

	     -s jsize  Specifies size of the journal if only one provider is
		       used for both data and journal.	The default is one
		       gigabyte.  Size should be chosen based on provider's
		       load, and not on its size; recommended minimum is twice
		       the size of the physical memory installed.  It is not
		       recommended to use gjournal for small file systems
		       (e.g.: only few gigabytes big).

     clear   Clear metadata on the given providers.

     stop    Stop the given provider.

	     Additional options include:

	     -f	 Stop the given provider even if it is opened.

     sync    Trigger journal switch and enforce sending data to the data
	     provider.

     dump    Dump metadata stored on the given providers.

     list    See geom(8).

     status  See geom(8).

     load    See geom(8).

     unload  See geom(8).

     Additional options include:

     -v	 Be more verbose.

EXIT STATUS
     Exit status is 0 on success, and 1 if the command fails.

EXAMPLES
     Create a gjournal based UFS file system and mount it:

	   gjournal load
	   gjournal label da0
	   newfs -J /dev/da0.journal
	   mount -o async /dev/da0.journal /mnt

     Configure journaling on an existing file system, but only if gjournal
     allows this (i.e., if the last sector is not already used by the file
     system):

	   umount /dev/da0s1d
	   gjournal label da0s1d da0s1e && \
	       tunefs -J enable -n disable da0s1d.journal && \
	       mount -o async /dev/da0s1d.journal /mnt || \
	       mount /dev/da0s1d /mnt

SYSCTLS
     Gjournal adds the sysctl level kern.geom.journal.	The string and integer
     information available is detailed below.  The changeable column shows
     whether a process with appropriate privilege may change the value.

	   sysctl name		       Type	     Changeable
	   debug		       integer	     yes
	   switch_time		       integer	     yes
	   force_switch		       integer	     yes
	   parallel_flushes	       integer	     yes
	   accept_immediately	       integer	     yes
	   parallel_copies	       integer	     yes
	   record_entries	       integer	     yes
	   optimize		       integer	     yes

     debug   Setting a non-zero value enables debugging at various levels.
	     Debug level 1 will record actions at a journal level, relating to
	     journal switches, metadata updates, etc.  Debug level 2 will
	     record actions at a higher level, relating to the numbers of
	     entries in journals, access requests, etc.	 Debug level 3 will
	     record verbose detail, including insertion of I/Os to the jour‐
	     nal.

     switch_time
	     The maximum number of seconds a journal is allowed to remain open
	     before switching to a new journal.

     force_switch
	     Force a journal switch when the journal uses more than N% of the
	     free journal space.

     parallel_flushes
	     The number of flush I/O requests to be sent in parallel when
	     flushing the journal to the data provider.

     accept_immediately
	     The maximum number of I/O requests accepted at the same time.

     parallel_copies
	     The number of copy I/O requests to send in parallel.

     record_entries
	     The maximum number of record entries to allow in a single jour‐
	     nal.

     optimize
	     Controls whether entries in a journal will be optimized by com‐
	     bining overlapping I/Os into a single I/O and reordering the
	     entries in a journal.  This can be disabled by setting the sysctl
	     to 0.

   cache
     The string and integer information available for the cache level is
     detailed below.  The changeable column shows whether a process with
     appropriate privilege may change the value.

	   sysctl name		   Type		 Changeable
	   used			   integer	 no
	   limit		   integer	 yes
	   divisor		   integer	 no
	   switch		   integer	 yes
	   misses		   integer	 yes
	   alloc_failures	   integer	 yes

     used    The number of bytes currently allocated to the cache.

     limit   The maximum number of bytes to be allocated to the cache.

     divisor
	     Sets the cache size to be used as a proportion of kmem_size.  A
	     value of 2 (the default) will cause the cache size to be set to
	     1/2 of the kmem_size.

     switch  Force a journal switch when this percentage of cache has been
	     used.

     misses  The number of cache misses, when data has been read, but was not
	     found in the cache.

     alloc_failures
	     The number of times memory failed to be allocated to the cache
	     because the cache limit was hit.

   stats
     The string and integer information available for the statistics level is
     detailed below.  The changeable column shows whether a process with
     appropriate privilege may change the value.

	   sysctl name		  Type		Changeable
	   skipped_bytes	  integer	yes
	   combined_ios		  integer	yes
	   switches		  integer	yes
	   wait_for_copy	  integer	yes
	   journal_full		  integer	yes
	   low_mem		  integer	yes

     skipped_bytes
	     The number of bytes skipped.

     combined_ios
	     The number of I/Os which were combined by journal optimization.

     switches
	     The number of journal switches.

     wait_for_copy
	     The number of times the journal switch process had to wait for
	     the previous journal copy to complete.

     journal_full
	     The number of times the journal was almost full, forcing a jour‐
	     nal switch.

     low_mem
	     The number of times the low_mem hook was called.

SEE ALSO
     geom(4), geom(8), mount(8), newfs(8), tunefs(8), umount(8)

HISTORY
     The gjournal utility appeared in FreeBSD 7.0.

AUTHORS
     Pawel Jakub Dawidek ⟨pjd@FreeBSD.org⟩

BSD			       February 17, 2009			   BSD
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