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54 Understanding Veritas Volume Manager
Online relayout
Online relayout
Note: You need a full 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 294 for details of how to perform
online relayout of volumes in VxVM. Also see “Converting between layered and
non-layered volumes” on page 300 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 System)
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.
The transformation is done by moving one portion of data at a time in the source
layout to the destination layout. Data is copied from the source volume to the
temporary area, and data is removed from the source volume storage area in
portions. The source volume storage area is then transformed to the new layout,
and the data saved in the temporary area 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.
The default size of the temporary area used during the relayout depends on the
size of the volume and the type of relayout. For volumes larger than 50MB, the