Creating a mirrored volume

A mirrored volume provides data redundancy by containing more than one copy of its data. Each copy (or mirror) is stored on different disks from the original copy of the volume and from other mirrors. Mirroring a volume ensures that its data is not lost if a disk in one of its component mirrors fails.

A mirrored volume requires space to be available on at least as many disks in the disk group as the number of mirrors in the volume.

If you specify layout=mirror, vxassist determines the best layout for the mirrored volume. Because the advantages of the layouts are related to the size of the volume, vxassist selects the layout based on the size of the volume. For smaller volumes, vxassist uses the simpler mirrored concatenated (mirror-concat) layout. For larger volumes, vxassist uses the more complex concatenated mirror (concat-mirror) layout. The attribute stripe-mirror-col-split-trigger-pt controls the selection. Volumes that are smaller than stripe-mirror-col-split-trigger-pt are created as mirror-concat, and volumes that are larger are created as concat-mirror. By default, the attribute stripe-mirror-col-split-trigger-pt is set to one gigabyte. The value can be set in /etc/default/vxassist. If there is a reason to implement a particular layout, you can specify layout=mirror-concat or layout=concat-mirror to implement the desired layout.

To create a new mirrored volume, use the following command:

# vxassist [-b] [-g diskgroup] make volume length \
  layout=mirror [nmirror=number] [init=active]

Specify the -b option if you want to make the volume immediately available for use.

For example, to create the mirrored volume, volmir, in the disk group, mydg, use the following command:

# vxassist -b -g mydg make volmir 5g layout=mirror

To create a volume with 3 instead of the default of 2 mirrors, modify the command to read:

# vxassist -b -g mydg make volmir 5g layout=mirror nmirror=3