VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager
Volume Manager and RAID-5
Chapter 148
Volume Manager and RAID-5
NOTE You may need an additional license to use this feature.
This section describes how Volume Manager implements RAID-5. For
general information on RAID-5, see “RAID-5”.
Although both mirroring (RAID-1) and RAID-5 provide redundancy of
data, they use different methods. Mirroring provides data redundancy by
maintaining multiple complete copies of the data in a volume. Data being
written to a mirrored volume is reflected in all copies. If a portion of a
mirrored volume fails, the system continues to use the other copies of the
data.
RAID-5 provides data redundancy by using parity. Parity is a calculated
value used to reconstruct data after a failure. While data is being written
to a RAID-5 volume, parity is calculated by doing an XOR procedure on
the data. The resulting parity is then written to the volume. If a portion
of a RAID-5 volume fails, the data that was on that portion of the failed
volume can be recreated from the remaining data and parity
information.
Traditional RAID-5 Arrays
A traditional RAID-5 array is several disks organized in rows and
columns. A column is a number of disks located in the same ordinal
position in the array. A row is the minimal number of disks necessary to
support the full width of a parity stripe. Figure 1-15, Traditional RAID-5
Array, shows the row and column arrangement of a traditional RAID-5
array.