VERITAS Volume Manager 3.1 Administrator's Guide

Volume Manager Operations
Online Relayout
Chapter 398
How Online Relayout Works
The VERITAS Online Relayout feature allows you to change storage
layouts that you have already created in place, without disturbing data
access. You can change the performance characteristics of a particular
layout to suit changed requirements.
For example, if a striped layout with a 128K stripe unit size is not
providing optimal performance, change the stripe unit size of the layout
by using the Relayout feature. You can transform one layout to another
by invoking a single command.
File systems mounted on the volumes do not need to be unmounted to
achieve this transformation as long as the file system provides online
shrink and grow operations.
Online Relayout reuses the existing storage space and has space
allocation policies to address the needs of the new layout. The layout
transformation process converts a given volume to the destination layout
by using minimal temporary space.
The transformation is done by moving a portion-at-a-time of data in the
source layout to the destination layout. Data is copied from the source
volume to the temporary space, which removes data from the source
volume storage area in portions. The source volume storage area is then
transformed to the new layout and data saved in the temporary space is
written back to the new layout. This operation is repeated until all the
storage and data in the source volume has been transformed to the new
layout.
You can use Online Relayout to change the number of columns, change
stripe width, remove and add parity, and change RAID-5 to mirroring.
Types of Transformation
At least one of the following criteria must be met for an Online Relayout
operation to be effective. You must perform one or more of the following
operations:
• RAID-5 to or from mirroring
• change the number of columns
• change the stripe width
• remove or add parity