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 systems, 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 cooperate with the gjournal provider below.  There are important dif-
     ferences 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 synchro-
     nization 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 mem-
		       ory 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 journal.

     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 journal.

     optimize
	     Controls whether entries in a journal will be optimized by combining 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 journal 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