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

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>