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

General Concepts
2 VERITAS Storage Foundation CDS Administrator’s Guide
Sharing Data Across Platforms
It must be emphasized that, while volumes can be exported across platforms, the data on the
volumes can be shared only if data sharing is supported at the application level. That is, to make
data sharing across platforms possible, it must be supported throughout the entire software stack.
For example, if a VxFS file system on a VxVM volume contains files comprising a database, then:
◆ Disks can be recognized (as cds disks) across platforms.
◆ Disk groups can be imported across platforms
◆ The file system can be mounted on different platforms
However, it is very likely that, because of the inherent characteristics of databases, you may not be
able to start up and use the database on a platform different from the one on which it was created.
Another example is where an executable file, compiled on one platform, can be accessed across
platforms (using CDS), but may not be executable on a different platform.
Note You do not need a file system in the stack if the operating system provides access to raw
disks and volumes, and the application can utilize them. In this way, databases and other
applications can have their data components built on top of raw volumes without having a
file system to store their data files.
Sector Size
Sector size is an attribute of a disk drive (or SCSI LUN for an array-type device), which is set when
the drive is formatted. Sectors are the smallest addressable unit 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
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:
◆ 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