Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

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.
The following error message displays the number of blocks required if there is
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.
As well as the temporary area, space is required for a temporary intermediate
volume when increasing the column length of a striped volume. The amount of
space required is the difference between the column lengths of the target and
source volumes. For example, 20GB of temporary additional space is required to
relayout a 150GB striped volume with 5 columns of length 30GB as 3 columns of
length 50GB. In some cases, the amount of temporary space that is required is
relatively large. For example, a relayout of a 150GB striped volume with 5 columns
as a concatenated volume (with effectively one column) requires 120GB of space
for the intermediate volume.
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.
55Understanding Veritas Volume Manager
Online relayout