VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager
Virtual Object Data Organization (Volume Layouts)
Chapter 1 41
to one column. Each column contains one or more subdisks and can be
derived from one or more physical disks. The number and sizes of
subdisks per column can vary. Additional subdisks can be added to
columns, as necessary.
CAUTION Striping a volume, or splitting a volume across multiple disks, increases
the chance that a disk failure will result in failure of that volume. For
example, if five volumes are striped across the same five disks, then
failure of any one of the five disks will require that all five volumes be
restored from a backup. If each volume is on a separate disk, only one
volume has to be restored. Use mirroring or RAID-5 to substantially
reduce the chance that a single disk failure results in failure of a large
number of volumes.
Data is allocated in equal-sized units (stripe units of size called stripe
unit size) that are interleaved between the columns. Each stripe unit is
a set of contiguous blocks on a disk. The default stripe unit size is 64
kilobytes.
For example, if there are three columns in a striped plex and six stripe
units, data is striped over three physical disks, as shown in Figure 1-11,
Striping Across Three Disks (Columns),. In Figure 1-11, Striping Across
Three Disks (Columns),:
• the first and fourth stripe units are allocated in column 1
• the second and fifth stripe units are allocated in column 2
• the third and sixth stripe units are allocated in column 3