VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager
Online Relayout
Chapter 1 39
Online Relayout
NOTE You may need an additional license to use this feature.
Online relayout allows you to convert between storage layouts in VxVM,
with uninterrupted data access. Typically, you would do this to change
the redundancy or performance characteristics of a volume. VxVM adds
redundancy to storage either by duplicating the data (mirroring) or by
adding parity (RAID-5). Performance characteristics of storage in VxVM
can be changed by changing the striping parameters, which are the
number of columns and the stripe width.
See “Performing Online Relayout” on page 318 for details of how to
perform online relayout of volumes in VxVM. Also see “Converting
Between Layered and Non-Layered Volumes” on page 322 for
information about the additional volume conversion operations that are
possible.
How Online Relayout Works
Online relayout allows you to change the 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 your
changed requirements. You can transform one layout to another by
invoking a single command.
For example, if a striped layout with a 128KB stripe unit size is not
providing optimal performance, you can use relayout to change the stripe
unit size.
File systems mounted on the volumes do not need to be unmounted to
achieve this transformation provided that the file system (such as
VERITAS File SystemTM) supports 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 that is available in the disk group.