VERITAS Storage Foundation 4.1 Cross-Platform Data Sharing Administrator's Guide

CDS Disk Access and Format
4 VERITAS Storage Foundation CDS Administrator’s Guide
CDS Disk Types
The CDS disk format, cdsdisk, is recognized by all VxVM platforms (including Windows). This
is the default disk format for all newly created VM disks unless overridden in a defaults file (see
“Defaults Files” on page 17). The vxcdsconvert utility is provided to convert other disk
formats and types to CDS.
Note Disks with format cdsdisk can only be added to disk groups with version 110 or later.
Private and Public Regions
A VM disk usually has a private and a public region.
The private region is a small area on the disk where VxVM configuration information is stored,
such as a disk header label, configuration records for VxVM objects (such as volumes, plexes and
subdisks), and an intent log for the configuration database. The default private region size is 2048
blocks (equivalent to 1024 kilobytes on AIX, Linux and the Solaris OS, and 2048 kilobytes on
HP-UX), which is large enough to record the details of about 4000 VxVM objects in a disk group.
The public region covers the remainder of the disk, and is used for the allocation of storage space to
subdisks.
The private and public regions are aligned and sized in multiples of 8K to permit the operation of
CDS. The alignment of VxVM objects within the public region is controlled by the disk group
alignment attribute. The value of this attribute must also be 8k to permit the operation of CDS.
Note With other (non-CDS) VxVM disk formats, the private and public regions are aligned to the
platform-specific OS block size.
Disk Access Type auto
The disk access (DA) disk type auto supports multiple disk formats, including cdsdisk, which is
supported across all platforms. It is associated with the DA records created by the VxVM
auto-configuration mode. Disk type auto automatically determines which format is on the disk.
Platform Block
The Platform Block resides on disk sector 0, and contains data specific to the Operating System for
the platforms. It is necessary for proper interaction with each of those platforms. The platform
block allows a disk to perform as if it was initialized by each of the specific platforms.