NAME¶
gmirror —
control utility for mirrored
devices
SYNOPSIS¶
gmirror |
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 ... |
DESCRIPTION¶
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
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 writing.
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 bigger 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 system
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 components. 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 system
crash.
- -F
- Do not synchronize after a power failure or system
crash. Assumes device is in consistent state.
- -h
- Hardcode providers' names in metadata.
- -n
- Turn off autosynchronization of stale components.
- -p
priority
- Specifies priority for the given component
prov.
- -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).
- 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 component 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 prefer balance algorithm will read from the next one,
thus will find nothing there.
SEE ALSO¶
geom(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.