Break-off snapshots are suitable for write-intensive volumes, such as database redo logs.
To turn one or more existing plexes in a volume into a break-off instant snapshot volume, the volume must be a non-layered volume with a mirror
or mirror-stripe
layout, or a RAID-5 volume that you have converted to a special layered volume and then mirrored. The plexes in a volume with a stripe-mirror
layout are mirrored at the subvolume level, and cannot be broken off.
See "Using a DCO and DCO volume with a RAID-5 volume" on page 286.
The attributes for a snapshot are specified as a tuple to the vxsnap
make
command. This command accepts multiple tuples. One tuple is required for each snapshot that is being created. Each element of a tuple is separated from the next by a slash character (/). Tuples are separated by white space.
To create and manage a third-mirror break-off snapshot
ACTIVE
plexes in the volume, or you can use the following command to add new snapshot mirrors to the volume:
# vxsnap [-b] [-g
diskgroup
] addmir
volume
[nmirror=
N] \
By default, the vxsnap
addmir
command adds one snapshot mirror to a volume unless you use the nmirror
attribute to specify a different number of mirrors. The mirrors remain in the SNAPATT
state until they are fully synchronized. The -b
option can be used to perform the synchronization in the background. Once synchronized, the mirrors are placed in the SNAPDONE
state.
For example, the following command adds 2 mirrors to the volume, vol1
, on disks mydg10
and mydg11
:
# vxsnap -g mydg addmir vol1 nmirror=2 alloc=mydg10,mydg11
If you specify the -b
option to the vxsnap
addmir
command, you can use the vxsnap
snapwait
command to wait for synchronization of the snapshot plexes to complete, as shown in this example:
vxsnap
make
command.
# vxsnap [-g
diskgroup
] make source=
volume[/newvol=
snapvol
]\
{/plex=
plex1
[,
plex2
,...]|/nmirror=
number
]}
Either of the following attributes may be specified to create the new snapshot volume, snapvol, by breaking off one or more existing plexes in the original volume:
plex
Specifies the plexes in the existing volume that are to be broken off. This attribute can only be used with plexes that are in the ACTIVE
state.
nmirror
Specifies how many plexes are to be broken off. This attribute can only be used with plexes that are in the SNAPDONE
state. (Such plexes could have been added to the volume by using the vxsnap
addmir
command.)
Snapshots that are created from one or more ACTIVE
or SNAPDONE
plexes in the volume are already synchronized by definition.
For backup purposes, a snapshot volume with one plex should be sufficient.
For example, to create the instant snapshot volume, snap2myvol
, of the volume, myvol
, in the disk group, mydg
, from a single existing plex in the volume, use the following command:
# vxsnap -g mydg make source=myvol/newvol=snap2myvol\
The next example shows how to create a mirrored snapshot from two existing plexes in the volume:
# vxsnap -g mydg make source=myvol/newvol=snap2myvol\
fsck
(or some utility appropriate for the application running on the volume) to clean the temporary volume's contents. For example, you can use this command with a VxFS file system:
The specified device must have a valid entry in the /etc/fstab
file.
See "Restoring a volume from an instant snapshot" on page 345.