LVM mirror pools in AIX 6 make it possible to divide the physical volumes of a scalable volume group into separate pools. When creating a logical volume, each opy of the logical volume being created can be assigned to a mirror pool. Logical volume copies that are assigned to a mirror pool will only allocate partitions from the physical volumes in that mirror pool. This provides the ability to restrict the disks that a logical volume copy can use. Without mirror pools, the only way to restrict which physical volume is used for allocation when creating or extending a logical volume is to use a map file. Thus, using mirror pools greatly simplify this process.
Assume a scalable volume group 'myvg' consisting of the following:
- physical volumes hdisk2 and hdisk3, which originate from a storage box in computer room ABC.
- physical volumes hdisk4 and hdisk5, which originate from a storage box in computer room DEF.
- logical volume 'mylv', which uses a parallel write with sequential read scheduling policy. This means that all mirrors are written in parallel but always read from the first mirror if the first mirror is available. This setting can improve sequential data access on the backend storage box significantly. Using this scheduling policy, there is primary and one (or possibly two) secondary copy (copies) of a physical partition.
- log logical volume loglv01.
Converting a scalable volume group / logical volumes to use mirror pools can be done as follows:
- Attach a mirror pool to the hdisks.
# chpv -p ABC hdisk2
# chpv -p ABC hdisk3
# chpv -p DEF hdisk4
# chpv -p DEF hdisk5
- Next, add the respective mirror pools to each existing logical volume in the volume group.
# chlv -m copy1=ABC -m copy2=DEF mylv
# chlv -m copy1=ABC -m copy2=DEF loglv01
- Set the mirror pool strictness to 'super'. This means that each newly created logical volume in the volume group must be assigned to a mirror pool and that each mirror pool must contain at least one copy of each logical volume in the volume group.
# chvg -M s myvg
- Check the status of the mirror pools
# lsvg -m myvg
Logical Volume Copy 1 Copy 2 Copy 3
loglv01 ABC DEF None
mylv ABC DEF None
# lsmp myvg
VOLUME GROUP: myvg Mirror Pool Super Strict: yes
MIRROR POOL: ABC Mirroring Mode: SYNC
MIRROR POOL: DEF Mirroring Mode: SYNC
Now when increasing the size of the file system built on top of mylv, there is no need to worry about the remote mirroring anymore.