Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Limitations of online relayout
Note the following limitations of online relayout:
■ Log plexes cannot be transformed.
■ Volume snapshots cannot be taken when there is an online relayout operation
running on the volume.
■ Online relayout cannot create a non-layered mirrored volume in a single step.
It always creates a layered mirrored volume even if you specify a non-layered
mirrored layout, such as mirror-stripe or mirror-concat. Use the vxassist
convert command to turn the layered mirrored volume that results from a
relayout into a non-layered volume.
See “Converting between layered and non-layered volumes” on page 381.
■ The usual restrictions apply for the minimum number of physical disks that
are required to create the destination layout. For example, mirrored volumes
require at least as many disks as mirrors, striped and RAID-5 volumes require
at least as many disks as columns, and striped-mirror volumes require at least
as many disks as columns multiplied by mirrors.
■ To be eligible for layout transformation, the plexes in a mirrored volume must
have identical stripe widths and numbers of columns. Relayout is not possible
unless you make the layouts of the individual plexes identical.
■ Online relayout cannot transform sparse plexes, nor can it make any plex
sparse. (A sparse plex is a plex that is not the same size as the volume, or that
has regions that are not mapped to any subdisk.)
■ The number of mirrors in a mirrored volume cannot be changed using relayout.
Instead, use alternative commands, such as the vxassist mirror command.
■ Only one relayout may be applied to a volume at a time.
Transformation characteristics
Transformation of data from one layout to another involves rearrangement of
data in the existing layout to the new layout. During the transformation, online
relayout retains data redundancy by mirroring any temporary space used. Read
and write access to data is not interrupted during the transformation.
Data is not corrupted if the system fails during a transformation. The
transformation continues after the system is restored and both read and write
access are maintained.
You can reverse the layout transformation process at any time, but the data may
not be returned to the exact previous storage location. Before you reverse a
transformation that is in process, you must stop it.
55Understanding Veritas Volume Manager
Online relayout