Veritas Storage Foundation Cross-Platform Data Sharing 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

16 Overview of CDS
Disk group alignment
Alignment values
The disk group block alignment has two values: 1 block or 8k (8 kilobytes).
All CDS disk groups must have an alignment value of 8k.
All disk group versions before version 110 have an alignment value of 1 block,
and they retain this value if they are upgraded to version 110 or later.
A disk group that is not a CDS disk group, and which has a version of 110 and
later, can have an alignment value of either 1 block or 8k.
The alignment for all newly initialized disk groups in VxVM 4.0 and later
releases is 8k. This value, which is used when creating the disk group, cannot be
changed. However, the disk group alignment can be subsequently changed.
See “Changing the alignment of a non-CDS disk group” on page 29.
Note: The default usage of vxassist is to set the layout=diskalign attribute on
all platforms. The
layout attribute is ignored on 8K-aligned disk groups, which
means that scripts relying on the default may fail.
Dirty region log alignment
The location and size of each map within a dirty region log (DRL) must not
violate the disk group alignment for the disk group (containing the volume to
which the DRL is associated). This means that the region size and alignment of
each DRL map must be a multiple of the disk group alignment, which for CDS
disk groups is 8K. (Features utilizing the region size can impose additional
minimums and size increments over and above this restriction, but cannot
violate it.)
In a version 110 disk group, a traditional DRL volume has the following region
requirements:
■ Minimum region size of 512K
■ Incremental region size of 64K
In a version 110 disk group, a version 20 DCO volume has the following region
requirements:
■ Minimum region size of 16K
■ Incremental region size of 8K