Veritas Storage Foundation Portable Data Containers: Cross-Platform Data Sharing 5.0.1 Administrators Guide, HP-UX 11i v3, First Edition, November 2009

of storage on the drive, and are the units in which the device performs I/O. The
sector size is significant because it defines the atomic I/O size at the device level.
Any multi-sector writes which VxVM submits to the device driver are not
guaranteed to be atomic (by the SCSI subsystem) in the case of system failure.
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:
■ 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.
Addressing 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.
Bleed-over issues
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
■ Disk size cannot exceed 1 TB
■ Cannot be an EFI disk
■ Must be the entire physical disk (LUN)
13Overview of CDS
CDS disk access and format