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Editing: gvirstor.8
.\" Copyright (c) 2006-2011 Ivan Voras <ivoras@FreeBSD.org> .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $FreeBSD$ .\" .Dd October 1, 2013 .Dt GVIRSTOR 8 .Os .Sh NAME .Nm gvirstor .Nd "control utility for virtual data storage devices" .Sh SYNOPSIS .Nm .Cm label .Op Fl hv .Op Fl s Ar virsize .Op Fl m Ar chunksize .Ar name .Ar prov ... .Nm .Cm stop .Op Fl fv .Ar name ... .Nm .Cm destroy .Op Fl fv .Ar name ... .Nm .Cm add .Op Fl vh .Ar name prov ... .Nm .Cm remove .Op Fl v .Ar name prov ... .Nm .Cm clear .Op Fl v .Ar prov ... .Nm .Cm dump .Ar prov ... .Nm .Cm list .Nm .Cm status .Nm .Cm load .Nm .Cm unload .Sh DESCRIPTION The .Nm utility is used for setting up a virtual storage device of arbitrary large size .Pq for example, several TB , consisting of an arbitrary number of physical storage devices with the total size which is equal to or smaller than the virtual size. Data for the virtual devices will be allocated from physical devices on demand. The idea behind .Nm is similar to the concept of Virtual Memory in operating systems, effectively allowing users to overcommit on storage .Pq free file system space . The concept is also known as "thin provisioning" in virtualization environments, only here it is implemented on the level of physical storage devices. .Pp The first argument to .Nm indicates an action to be performed: .Bl -tag -width ".Cm remove" .It Cm label Set up a virtual device from the given components with the specified .Ar name . Metadata is stored in the last sector of every component. Argument .Fl s Ar virsize is the size of new virtual device, with default being set to 2 TiB .Pq 2097152 MiB . Argument .Fl m Ar chunksize is the chunk size, with default being set to 4 MiB .Pq 4096 KiB . The default arguments are thus .Qq Fl s Ar 2097152 Fl m Ar 4096 . .It Cm stop Turn off an existing virtual device with the given .Ar name . This command does not touch on-disk metadata. As with other GEOM classes, stopped geoms cannot be started manually. .It Cm destroy Same as .Cm stop. .It Cm add Adds new components to existing virtual device with the given .Ar name . The specified virstor device must exist and be active .Pq i.e. module loaded, device present in Pa /dev . This action can be safely performed while the virstor device is in use .Pq Qo hot Qc operation . .It Cm remove Removes components from existing virtual device with the given .Ar name . Only unallocated providers can be removed. .It Cm clear Clear metadata on the given providers. .It Cm dump Dump metadata stored on the given providers. .It Cm list See .Xr geom 8 . .It Cm status See .Xr geom 8 . .It Cm load See .Xr geom 8 . .It Cm unload See .Xr geom 8 . .El .Pp Additional options: .Bl -tag -width ".Fl f" .It Fl f Force the removal of the specified virtual device. .It Fl h Hardcode providers' names in metadata. .It Fl v Be more verbose. .El .Sh EXAMPLES The following example shows how to create a virtual device of default size .Pq 2 TiB , of default chunk .Pq extent size .Pq 4 MiB , with two physical devices for backing storage. .Bd -literal -offset indent .No gvirstor label -v Ar mydata Ar /dev/ada4 Ar /dev/ada6 .No newfs Ar /dev/virstor/mydata .Ed .Pp From now on, the virtual device will be available via the .Pa /dev/virstor/mydata device entry. To add a new physical device / component to an active virstor device: .Bd -literal -offset indent .No gvirstor add Ar mydata Ar ada8 .Ed .Pp This will add physical storage of .Ar ada8 to .Pa /dev/virstor/mydata device. .Pp To see the device status information .Pq including how much physical storage is still available for the virtual device , use: .Bd -literal -offset indent gvirstor list .Ed .Pp All standard .Xr geom 8 subcommands .Pq e.g. Cm status , Cm help are also supported. .Sh SYSCTL VARIABLES .Nm has several .Xr sysctl 8 tunable variables. .Bd -literal -offset indent .Va int kern.geom.virstor.debug .Ed .Pp This sysctl controls verbosity of the kernel module, in the range 1 to 15. Messages that are marked with higher verbosity levels than this are suppressed. Default value is 5 and it is not recommended to set this tunable to less than 2, because level 1 messages are error events, and level 2 messages are system warnings. .Bd -literal -offset indent .Va int kern.geom.virstor.chunk_watermark .Ed .Pp Value in this sysctl sets warning watermark level for physical chunk usage on a single component. The warning is issued when a virstor component has less than this many free chunks .Pq default 100 . .Bd -literal -offset indent .Va int kern.geom.virstor.component_watermark .Ed .Pp Value in this sysctl sets warning watermark level for component usage. The warning is issued when there are less than this many unallocated components .Pq default is 1 . .Pp All these sysctls are also available as .Xr loader 8 tunables. .Sh DIAGNOSTICS .Ex -std .Pp .Nm kernel module issues log messages with prefixes in standardized format, which is useful for log message filtering and dispatching. Each message line begins with .Bd -literal -offset indent .Li GEOM_VIRSTOR[%d]: .Ed .Pp The number .Pq %d is message verbosity / importance level, in the range 1 to 15. If a message filtering, dispatching or operator alert system is used, it is recommended that messages with levels 1 and 2 be taken seriously .Pq for example, to catch out-of-space conditions as set by watermark sysctls. .Sh SEE ALSO .Xr geom 4 , .Xr fstab 5 , .Xr geom 8 , .Xr glabel 8 , .Xr newfs 8 .Sh HISTORY The .Nm utility first appeared in .Fx 7.0 . .Sh AUTHORS .An Ivan Voras Aq Mt ivoras@FreeBSD.org .Pp Sponsored by Google Summer of Code 2006. .Sh BUGS Commands .Cm add and .Cm remove contain unavoidable critical sections which may make the virstor device unusable if a power failure .Pq or other disruptive event happens during their execution. It is recommended to run them when the system is quiescent. .Sh ASSUMPTIONS AND INTERACTION WITH FILE SYSTEMS There are several assumptions that .Nm has in its operation: that the size of the virtual storage device will not change once it is set, and that the sizes of individual physical storage components will always remain constant during their existence. For alternative ways to implement virtual or resizable file systems see .Xr zfs 1M , .Xr gconcat 8 and .Xr growfs 8 . .Pp Note that .Nm has nontrivial interaction with file systems which initialize a large number of on-disk structures during newfs. If such file systems attempt to spread their structures across the drive media .Pq like UFS/UFS2 does , their efforts will be effectively foiled by sequential allocation of chunks in .Nm and all their structures will be physically allocated at the start of the first virstor component. This could have a significant impact on file system performance .Pq which can in some rare cases be even positive .
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