Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

50 Understanding Veritas Volume Manager

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 286 for details of how to perform online

relayout of volumes in VxVM. Also see “Converting between layered and non-layered

volumes” on page 292 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 amount of temporary

space that is required is usually 10% of the size of the volume, from a minimum of 50MB

up to a maximum of 1GB. For volumes smaller than 50MB, the temporary space required

is the same as the size of the volume.