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gjournal

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

NAME

gjournalcontrol 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⟩
February 17, 2009 Debian Sid