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gjournal(8) [freebsd man page]

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
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