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Man Pages


Manual Reference Pages  -  GJOURNAL (8)

NAME

gjournal - control utility for journaled devices

CONTENTS

Synopsis
Description
Exit Status
Examples
Sysctls
See Also
History
Authors

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 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
.Fx 7.0 .

AUTHORS


.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org
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