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GJOURNAL(8)             FreeBSD 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
     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

     Li 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

     Li 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

     Li 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>

FreeBSD 11.0-PRERELEASE        February 17, 2009       FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | EXIT STATUS | EXAMPLES | SYSCTLS | SEE ALSO | HISTORY | AUTHORS

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