NAME
gmirror — control utility for mirrored devices
SYNOPSIS
gmirror label
[−hnv] [−b balance]
[−s slice] name prov
[prov [...]]
gmirror clear [−v] prov
[prov [...]]
gmirror configure [−adhnv]
[−b balance]
[−s slice] name
gmirror rebuild [−v] name prov
[prov [...]]
gmirror insert [−hiv]
[−p priority] name prov
[prov [...]]
gmirror remove [−v] name prov
[prov [...]]
gmirror activate [−v] name prov
[prov [...]]
gmirror deactivate [−v] name prov
[prov [...]]
gmirror forget [−v] name
[name [...]]
gmirror stop [−fv] name
[name [...]]
gmirror list [name [...]]
gmirror load [−v]
gmirror unload [−v]
DESCRIPTION
The gmirror utility is used for mirrors (RAID1) configuration. After a mirror creation, all components are detected and configured automatically. All operations like failure detection, stale components detection, rebuild of stale components etc. are done automatically as well. The gmirror utility uses on-disk metadata (the last provider’s sector) to store all needed information. Since the last sector is used for this purpose, it is possible to place a root file system on a mirror.
The first argument to gmirror indicates an action to be performed:
label
Create a mirror. Components order is important, because priority is based on its position (starting from 0). Component with the biggest priority is used by prefer balance algorithm and also is used as a master component when resynchronization is needed after, e.g. a power failure if device was open for writing.
Additional options include:
−b balance
Specifies balance algorithm to use, one of:
load
Read from the component with the lowest load.
prefer
Read from the component with the biggest priority.
round-robin
Use round-robin algorithm when choosing component to read.
split
Split read requests, which are bigger than or equal to slice size on N pieces, where N is the number of active components.
−h
Hardcode providers’ names in metadata.
−n
Turn off autosynchronization of stale components.
−s slice
When using split balance algorithm and I/O READ request is bigger than or equal to this value, I/O request will be split into N pieces, where N is the number of active component.
clear
Clear metadata on the given providers.
configure
Configure the given device.
Additional options include:
−a
Turn on autosynchronization of stale components.
−b balance
Specifies balance algorithm to use.
−d
Do not hardcode providers’ names in metadata.
−h
Hardcode providers’ names in metadata.
−n
Turn off autosynchronization of stale components.
−s slice
Specifies slice size for split balance algorithm.
rebuild
Rebuild the given mirror components forcibly. If autosynchronization wasn’t turn off for the given device, this command hopefully will not be used.
insert
Add the given component(s) to the existing mirror.
Additional options include:
−h
Hardcode providers’ names in metadata.
−i
Mark component(s) as inacitve immediatelly after insertion.
−p priority
Specifies priority of the given component(s).
remove
Remove the given component(s) from the mirror and clear metadata on it.
activate
Activate the given component(s), which were marked as inactive before.
deactivate
Mark the given component(s) as inactive, so it will not be automatically connected to the mirror.
forget
Forget about components which are not connected. This command is useful when disk failed and can’t be reconnected, so remove command can’t be used to remove it.
stop
Stop the given mirror.
Additional options include:
−f
Stop the given mirror even if it is opened.
list
List every currently configured devices, if a list of devices is passed as a parameter then only those devices will be shown.
load
Load geom_mirror.ko kernel module.
unload
Unload geom_mirror.ko kernel module.
Additional options include:
−v
Be more verbose.
EXAMPLES
Use 3 disks to setup a mirror. Choose split balance algorithm, split only requests which are bigger than or equal to 2kB. Create file system, mount it, then unmount it and stop device:
gmirror label
-v -b split -s 2048 data da0 da1 da2
newfs /dev/mirror/data
mount /dev/mirror/data /mnt
[...]
umount /mnt
gmirror stop data
gmirror unload
Create a mirror on disk with valid data. Add another disk to this mirror, so it will be synchronized with existing disk:
gmirror label
-v -b round-robin data da0
gmirror insert data da1
Create a mirror, but do not use automatic sunchronization feature. Add another disk and rebuild it:
gmirror label
-v -n -b load data da0 da1
gmirror insert data da2
gmirror rebuild data da2
One disk failed. Replace it with a brand new one:
gmirror forget
data
gmirror insert data da1
Create a mirror, deactivate one component, do the backup and connect it again. It will not be resynchronized, if there is no need to (there were no writes in the meantime):
gmirror label
data da0 da1
gmirror deactivate data da1
dd if=/dev/da1 of=/backup/data.img bs=1m
gmirror activate data da1
NOTES
If you are using swap-on-mirror configuration be sure to put:
swapoff="YES"
into your /etc/rc.conf and use shutdown(8) command to reboot/shutdown your system.
DIAGNOSTICS
Exit status is 0 on success, and 1 if the command fails.
SEE ALSO
geom(4), geom(8), mount(8), newfs(8), umount(8), vinum(8)
HISTORY
The gmirror utility appeared in FreeBSD 5.3.
AUTHORS
Pawel Jakub Dawidek <pjd [AT] FreeBSD.org>
BUGS
There should be a way to change component’s priority inside a running mirror.
There should be a section with implementation description.
BSD Jul 9, 2004 BSD