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GMIRROR (8) | System administration commands and daemons | Unix Manual Pages | :man


gmirror - "control utility for mirrored devices"


Exit Status
See Also


gmirror label [-hnv] [-b balance] [-s slice] name prov ... gmirror clear [-v] prov ... gmirror configure [-adhnv] [-b balance] [-s slice] name gmirror rebuild [-v] name prov ... gmirror insert [-hiv] [-p priority] name prov ... gmirror remove [-v] name prov ... gmirror activate [-v] name prov ... gmirror deactivate [-v] name prov ... gmirror forget [-v] name ... gmirror stop [-fv] name ... gmirror clear [-v] prov ... gmirror dump prov ... gmirror list gmirror status gmirror load gmirror unload


The gmirror utility is used for mirror (RAID1) configurations. After a mirror’s creation, all components are detected and configured automatically. All operations like failure detection, stale component detection, rebuild of stale components, etc. are also done automatically. The gmirror utility uses on-disk metadata (stored in the provider’s last 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. The order of components is important, because a component’s priority is based on its position (starting from 0). The component with the biggest priority is used by the prefer balance algorithm and is also used as a master component when resynchronization is needed, e.g. after a power failure when the 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 the split balance algorithm and an I/O READ request is bigger than or equal to this value, the 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 was not turned off for the given device, this command should be unnecessary.
insert Add the given component(s) to the existing mirror.

Additional options include:

-h Hardcode providers’ names in metadata.
-i Mark component(s) as inactive immediately 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 a disk has failed and cannot be reconnected, preventing the remove command from being used to remove it.
stop Stop the given mirror.

Additional options include:

-f Stop the given mirror even if it is opened.
dump Dump metadata stored on the given providers.
list See geom(8).
See geom(8).
load See geom(8).
See geom(8).

Additional options include:

-v Be more verbose.


Exit status is 0 on success, and 1 if the command fails.


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 (note that the last sector of the disk will be overwritten). 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 synchronization 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 do so (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


geom(4), geom(8), mount(8), newfs(8), umount(8), vinum(8)




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