Non-Strict Disk Mirroring

Audience: System Administrators

Date: July 22, 2002

The "non-strick" AIX mirroring option can be used to mirror data over fewer disks compared to the traditional "strict" mirroring option. The attached diagram illustrates both options. In both cases, the data is protected from hardware failure as no two mirror copies reside on the same physical disk.

In this example, the non-strict option uses half the disk drives of the strict option. However, this can be customized this using the "mklv" command:

mklv -y strict_lv -e x -c 2 datavg 3 hdisk2 hdisk3 hdisk4

The view the physical partition layout:

lslv -m strict_lv

LP    PP1  PV1               PP2  PV2
0001  0017 hdisk2            0250 hdisk3
0002  0249 hdisk3            0104 hdisk4
0003  0103 hdisk4            0018 hdisk2

To replace a failed disk, use the "migratepv" command. Here are the steps to recover from a failed disk.

1. Backup the data
2. Pull the failed disk, let's call it hdisk4
3. Put in a new disk
4. Run: cfgmgr -l <disk adapter> and the new disk will show up, let's call it hdisk5
5. Run: extendvg <vgname> hdisk5
6. Run: migratepv hdisk4 hdisk5
7. Run: reducevg <vgname> hdisk4
8. Run: rmdev -dl hdisk4

PS Thanks Dan Braden for this tip.