vxcache

NAME

vxcache - administer the cache object for space-optimized snapshots

SYNOPSIS

DESCRIPTION

The vxcache utility is used to administer a cache object that is associated with volumes that have one or more space-optimized snapshots. The cache object, cacheobj, and underlying cache volume, cachevol, may be shared between volumes in a disk group.

KEYWORDS

att

Attaches a volume as a cache volume to a cache object. If a valid cache object exists but the original cache volume has been removed, this operation may be used to attach a new volume as a cache volume to the cache object.

dis

Dissociates one or more cache volumes from their cache objects.

growcacheby

Grows the cache by the specified amount, lengthchange.

growcacheto

Grows the cache to the specified length, newlength.

listvol

Prints a space-separated list of space-optimized instant snapshots that have been created on the specified cache object. This list is sorted by the timestamp on the snapshot. If two or more snapshots have the same timestamp, these snapshots are sorted in order of decreasing size.

set

Sets the value of an attribute for the specified cache objects. Values may be set for the autogrow, autogrowby, highwatermark and maxautogrow attributes. See the vxcached(1M) manual page for a description of these attributes.

shrinkcacheby

Shrinks the cache by the specified amount, lengthchange.

shrinkcacheto

Shrinks the cache to the specified length, newlength.

start

Starts cache objects and rebuilds the in-core mapping.

stat

Prints space usage statistics for cache objects:

TOTAL

Total size of the cache volume in megabytes that is available to cache data. As a small amount of space is required to hold cache object metadata, this value is always smaller than the total size of the cache volume.

USED

Size of the cache that is in use in megabytes and as a percentage.

AVAIL

Size of the cache that is available for use in megabytes and as a percentage.

SDCNT

Number of subdisks that have been created on the cache object.

If no cache objects are specified, statistics are displayed for all cache objects in the disk group.

stop

Stops cache objects.

OPTIONS

-d defaults

Specifies a file containing defaults for various attributes related to space allocation for growing and shrinking the cache. If not specified, this defaults to /etc/default/vxassist.

-f

Forces the stop operation if any snapshots have been created on a cache object.

-g diskgroup

Specifies the disk group for the operation, either by disk group ID or by disk group name. If this option is not specified, the default disk group is determined using the rules given in the vxdg(1M) manual page.

-n

Prevents the system defaults file being read.

HARDWARE-SPECIFIC OPTIONS

Some environments provide guidelines to optimize VxVM's interaction with intelligent storage systems. If these guidelines are present, VxVM follows them when allocating space for volumes.

The following options change the behavior of the growcacheby, growcacheto, shrinkcacheby and shrinkcacheto operations:

-o override

Performs the specified vxcache task for the specified volume and ignores any storage-specific guidelines. Overriding the guidelines is not recommended as it can result in incompatible objects, or objects that cannot be administered by VxVM and any associated software that exploit storage-specific features.

-o verify

Verifies that the vxcache task for the specified volume can be performed without violating any storage-specific guidelines, but does not commit or perform any task. If any guidelines are violated, vxcache exits with an error message.

Refer to the vendor-specific documentation for more information on how intelligent storage systems can interact with VxVM.

EXAMPLES

Create and enable a 1GB mirrored cache with a region size of 32KB:

Grow the cache volume, mydgcvol, that is associated with the cache object, mydgcobj, by 1GB:

Change the value of the maxautogrow attribute to 2GB for a cache:

Stop and restart the cache object, mydgcobj, which has entered the DETACHED state after a failed grow or shrink operation (the -f option to vxcache stop is required because snapshots exist on the cache object):

Stop the cache object, mydgcobj, and dissociate the cache volume, mydgcvol, from it:

NOTES

The attributes that may be specified with the growcacheby, growcacheto, shrinkcacheby and shrinkcacheto keywords are the same as for the vxassist command. See the vxassist(1M) manual page for details.

The vxcached daemon monitors the usage of cache objects. See the vxcached(1M) manual page for details.

The size of a cache volume must be greater than or equal to 5m (5MB).

SEE ALSO

vxassist (1M), vxcached (1M), vxintro (1M), vxmake (1M), vxsnap (1M), vxstat (1M)