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GMIRROR(8) FreeBSD System Manager's Manual GMIRROR(8) NAME gmirror -- control utility for mirrored devices SYNOPSIS gmirror label [-Fhnv] [-b balance] [-s slice] name prov ... gmirror clear [-v] prov ... gmirror create [-Fnv] [-b balance] [-s slice] name prov ... gmirror configure [-adfFhnv] [-b balance] [-s slice] name gmirror configure [-v] -p priority name prov gmirror rebuild [-v] name prov ... gmirror resize [-v] [-s size] name gmirror insert [-hiv] [-p priority] name prov ... gmirror remove [-v] name prov ... gmirror activate [-v] name prov ... gmirror deactivate [-v] name prov ... gmirror destroy [-fv] name ... 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, be- cause a component's priority is based on its position (start- ing 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 big- ger than or equal to slice size on N pieces, where N is the number of ac- tive 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. create Similar to label, but creates mirror without storing on-disk metadata in last sector. This special "manual" operation mode assumes some external control to manage mirror detection after reboot, device hot-plug and other external events. 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. resize Change the size of the given mirror. Additional options include: -s size New size of the mirror is expressed in logical block numbers. This option can be omitted, then it will be automatically calculated to maximum available size. 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. destroy Stop the given mirror and clear metadata on all its compo- nents. Additional options include: -f Stop the given mirror even if it is opened. 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 re- move 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 SYSCTL VARIABLES The following sysctl(8) variables can be used to configure behavior for all mirrors. kern.geom.mirror.debug Control the verbosity of kernel logging related to mirrors. A value larger than 0 will enable debug logging. kern.geom.mirror.timeout The amount of time, in seconds, to wait for all copies of a mir- ror to appear before starting the mirror. Disks that appear af- ter the mirror has been started are not automatically added to the mirror. kern.geom.mirror.idletime The amount of time, in seconds, which must elapse after the last write to a mirror before that mirror is marked clean. Clean mir- rors do not need to be synchronized after a power failure or sys- tem crash. A small value may result in frequent overwrites of the disks' metadata sectors, and thus may reduce the longevity of the disks. kern.geom.mirror.disconnect_on_failure Determine whether a disk is automatically removed from its mirror when an I/O request to that disk fails. kern.geom.mirror.sync_requests The number of parallel I/O requests used while synchronizing a mirror. This parameter may only be configured as a loader.conf(5) tunable. kern.geom.mirror.sync_update_period The period, in seconds, at which a synchronizing mirror's meta- data is updated. Periodic updates are used to record a synchro- nization's progress so that an interrupted synchronization may be resumed starting at the recorded offset, rather than at the be- ginning. A smaller value results in more accurate progress tracking, but also increases the number of non-sequential writes to the disk being synchronized. If the sysctl value is 0, no up- dates are performed until the synchronization is complete. NOTES Doing kernel dumps to gmirror providers is possible, but some conditions have to be met. First of all, a kernel dump will go only to one compo- nent and gmirror always chooses the component with the highest priority. Reading a dump from the mirror on boot will only work if the prefer bal- ance algorithm is used (that way gmirror will read only from the compo- nent with the highest priority). If you use a different balance algo- rithm, 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 ALSO geom(4), dumpon(8), geom(8), gvinum(8), mount(8), newfs(8), savecore(8), sysctl(8), umount(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. FreeBSD 13.0 November 30, 2017 FreeBSD 13.0
NAME | SYNOPSIS | DESCRIPTION | EXIT STATUS | EXAMPLES | SYSCTL VARIABLES | NOTES | SEE ALSO | HISTORY | AUTHORS | BUGS
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