GMIRROR(8) BSD System Manager's Manual GMIRROR(8)NAMEgmirror — control utility for mirrored devices
SYNOPSISgmirror label [-Fhnv] [-b balance] [-s slice] name prov ...
gmirror clear [-v] prov ...
gmirror configure [-adfFhnv] [-b balance] [-s slice] name
gmirror configure [-v] -p priority name prov
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 dump prov ...
gmirror list
gmirror status
gmirror load
gmirror unload
DESCRIPTION
The gmirror utility is used for mirror (RAID1) configurations. After a
mirror's creation, all components are detected and configured automati‐
cally. 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 sec‐
tor) 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 to 255). 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 writ‐
ing.
Additional options include:
-b balance Specifies balance algorithm to use, one of:
load Read from the component with the
lowest load. This is the default
balance algorithm.
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 big‐
ger than or equal to slice size on N
pieces, where N is the number of
active components.
-F Do not synchronize after a power failure or sys‐
tem crash. Assumes device is in consistent
state.
-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 compo‐
nents. Defaults to 4096 bytes.
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.
-f Synchronize device after a power failure or sys‐
tem crash.
-F Do not synchronize after a power failure or sys‐
tem crash. Assumes device is in consistent
state.
-h Hardcode providers' names in metadata.
-n Turn off autosynchronization of stale compo‐
nents.
-p priority Specifies priority for the given component prov.
-s slice Specifies slice size for split balance algo‐
rithm.
rebuild Rebuild the given mirror components forcibly. If autosyn‐
chronization 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 meta‐
data on it.
activate Activate the given component(s), which were marked as inac‐
tive 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 com‐
mand is useful when a disk has failed and cannot be recon‐
nected, 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).
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
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
NOTES
Doing kernel dumps to gmirror providers.
This is possible, but some conditions have to be met. First of all, a
kernel dump will go only to one component and gmirror always chooses the
component with the highest priority. Reading a dump from the mirror on
boot will only work if the prefer balance algorithm is used (that way
gmirror will read only from the component with the highest priority). If
you use a different balance algorithm, you should add:
gmirror configure -b prefer data
to the /etc/rc.early script and:
gmirror configure -b round-robin data
to the /etc/rc.local script. The decision which component to choose for
dumping is made when dumpon(8) is called. If on the next boot a compo‐
nent with a higher priority will be available, the prefer algorithm will
choose to read from it and savecore(8) will find nothing. If on the next
boot a component with the highest priority will be synchronized, the pre‐
fer balance algorithm will read from the next one, thus will find nothing
there.
SEE ALSOgeom(4), dumpon(8), geom(8), mount(8), newfs(8), savecore(8), umount(8),
vinum(8)HISTORY
The gmirror utility appeared in FreeBSD 5.3.
AUTHORS
Pawel Jakub Dawidek ⟨pjd@FreeBSD.org⟩
BUGS
There should be a way to change a component's priority inside a running
mirror.
There should be a section with an implementation description.
Documentation for sysctls kern.geom.mirror.* is missing.
BSD December 8, 2009 BSD
