Using Splitvg to make backups

If you need to backup a logical volume or volume group with the minimum amount of downtime the easiest way is to mirror it and then create a snapshot as follows:

mirrorvg [ -S | -s ] [ -Q ] [ -c copies] [ -m ] [ -p copyn=mirrorpool ] volumegroup [ physicalvolume ... ]

Now split off a copy of the mirror using the splitvg command

splitvg  [ -y SnapVGname ]  [ -c  Copy ] [ -f  ] [ -i ]  VGname
This splits a single mirror copy of a fully mirrored volume group into a snapshot volume group. The original volume group VGname will stop using the disks that are now part of the snapshot volume group SnapVGname.

This method can also be used to split-off copies of one or more logical-volumes.

Splitting copies of a logical volume

The splitlvcopy command splits copies from one logical volume and creates a new and separate logical volume from them. The general syntax of the splitlvcopy command is as follows:

splitlvcopy [ -f ] [ -y NewLogicalVolumeName ] [ -Y Prefix ] LogicalVolume

Copies [ PhysicalVolume ... ]

To split one copy of each logical partition belonging to the logical volume named

“oldlv” which currently has 3 copies of each logical partition, and create the logical volume “newlv”, use the splitlvcopy command as follows:

# splitlvcopy -y newlv oldlv 2

Each logical partition in the logical volume “oldlv” now has two physical partitions.

Each logical partition in the logical volume “newlv” now has one physical partition.

Mirroring is an LVM task that you perform only on logical volumes to migrate data. The following example shows how to create a mirror copy of a logical volume using the mklvcopy command:

# mklvcopy -e m -s y -k datalv 2 hdisk3 hdisk7

 .

 .

# splitlvcopy -y splitlv datalv 1

Once you have a split copy you can mount the filesystem elsewhere and back it up whilst the original is still being updated. Once finished you simply join the LV or VG and the mirrors are re-synced automatically.