GVIRSTOR(8) MidnightBSD System Manager’s Manual GVIRSTOR(8)

NAME

gvirstor — provides virtual data storage geom

SYNOPSIS

gvirstor label [−hv] [−s virsize] [−m chunksize] name prov ...
gvirstor stop [−fv] name ...
gvirstor add [−vh] name prov ...
gvirstor remove [−v] name prov ...
gvirstor clear [−v] prov ...
gvirstor dump prov ...
gvirstor list
gvirstor status
gvirstor load
gvirstor unload

DESCRIPTION

The gvirstor utility is used for setting up a storage device of arbitrary large size (for example, several TB), consisting of an arbitrary number of physical storage devices with total size <= the virtual size. Data for the virtual devices will be allocated from physical devices on demand. In short, this is the virtual storage functionality. The first argument to gvirstor indicates an action to be performed:

label

Set up a virtual device from the given components with the specified name. Metadata are stored in the last sector of every component. Argument virsize is the size of new virtual device, with default being 2 TiB (2097152 MiB). Argument chunksize is the chunk size, with default being 4 MiB (4096 KiB). The default is thus "-s 2097152 -m 4096".

stop

Turn off an existing virtual device by its name. This command does not touch on-disk metadata. As with other GEOM classes, stopped geoms cannot be started manually.

add

Adds new components to existing virtual device by its name. The specified virstor device must exist and be active (i.e. module loaded, device present in /dev).

remove

Removes components from existing virtual device by its name. Only unallocated providers can be removed.

clear

Clear metadata on the given providers.

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:

−f

Force the removal of the specified virtual device.

−h

Hardcode providers’ names in metadata.

−v

Be more verbose.

EXIT STATUS

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

EXAMPLES

The following example shows how to create a virtual device of default size (2 TiB), of default chunk (extent) size (4 MiB), with two physical devices for backing storage.

gvirstor label -v mydata /dev/ad4 /dev/ad6
newfs /dev/virstor/mydata

From now on, the virtual device will be available via the /dev/virstor/mydata device entry. To add a new physical device / provider to an active virstor device:

gvirstor add mydata ad8

This will add physical storage (from ad8) to /dev/virstor/mydata device. To see device status information (including how much physical storage is still available for the virtual device), use:

gvirstor list

All standard geom(8) subcommands (e.g. "status", "help") are also supported.

SYSCTLs

gvirstor has several sysctl(8) tunable variables.

int kern.geom.virstor.debug

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 supressed. Default value is 5 and it’s not recommented to set this tunable to less than 2, because level 1 messages are error events, and level 2 messages are system warnings.

int kern.geom.virstor.chunk_watermark

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 (default 100).

int kern.geom.virstor.component_watermark

Value in this sysctl sets warning watermark level for component usage. The warning is issed when there are less than this many unallocated components (default is 1).

All these sysctls are also available as loader(8) tunables.

LOG MESSAGES

gvirstor kernel module issues log messages with prefixes in standardised format, which is useful for log message filtering and dispatching. Each message line begins with

GEOM_VIRSTOR[%d]:

The number (%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 (for example, to catch out-of-space conditions as set by watermark sysctls).

SEE ALSO

geom(4), geom(8), newfs(8), fstab(5), glabel(8)

HISTORY

The gvirstor utility appeared in FreeBSD 7.0.

BUGS

Commands "add" and "remove" contain unavoidable critical sections which may make the virstor device unusable if a power failure (or other disruptive event) happens during their execution. It’s recommended to run them when the system is quiescent.

AUTHOR

Ivan Voras 〈ivoras@FreeBSD.org〉 Sponsored by Google Summer of Code 2006

MidnightBSD 0.3 July 8, 2006 MidnightBSD 0.3