VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Online Relayout
32 VERITAS Volume Manager Administrator’s Guide
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
TM
) 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 portionof data at a time inthe sourcelayout 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 sizeof thetemporary area used during the relayoutdepends onthe sizeof the
volume and the type of relayout. Forvolumes largerthan 50MB,the amountof 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.
The followingerrormessage displays the number of blocks required if thereis insufficient
free space available in the disk group for the temporary area:
tmpsize too small to perform this relayout (nblks minimum required)
You can override the default size used for the temporary area by using the tmpsize
attribute to vxassist. See the vxassist(1M) manual page for more information.
Additional permanent disk space may be required for the destination volumes,
depending on the type of relayout that you are performing. This may happen, for
example, if you change the number of columns in a striped volume. The figure, “Example
of Decreasing the Number of Columns in a Volume,” shows how decreasing the number
of columns can require disks to be added to a volume. The size of the volume remains the
same but an extra disk is needed to extend one of the columns.