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

11Overview of CDS
CDS disk access and format
Block size issues
The block size is a platform-dependent value that is greater than or equal to the
sector size. Each platform accesses the disk on block boundaries and in
quantities that are multiples of the block size.
Data that is created on one platform, and then accessed by a platform of a
different block size, can suffer from the following problems:
Operating system data
Some operating systems (OS) require OS-specific data on disks in order to
recognize and control access to the disk.
CDS disk access and format
For a disk to be accessible by multiple platforms, the disk must be consistently
recognized by the platforms, and all platforms must be capable of performing I/
O on the disk. CDS disks contain specific content at specific locations to identify
or control access to the disk on different platforms. The same content and
location are used on all CDS disks, independent of the platform on which the
disks are initialized.
In order for a disk to be initialized as, or converted to a CDS disk, it must satisfy
the following requirements:
■ Must be a SCSI disk that supports Mode Sense
■ Cannot be an EFI disk
■ Must be the entire physical disk (LUN)
■ Only one volume manager (such as VxVM) can manage a physical disk (LUN)
■ There can be no disk partition (slice) which is defined, but which is not
configured on the disk
Addressing issues ■ The data may not have been created on a block boundary
compatible with that used by the accessing platform.
■ The accessing platform cannot address the start of the
data.
Bleed-over issues The size of the data written may not be an exact multiple of the
block size used by the accessing platform. Therefore the
accessing platform cannot constrain its I/O within the
boundaries of the data on disk.