VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager

Volume Manager and RAID-5

Chapter 150

Figure 1-16 Volume Manager RAID-5 Array

With the Volume Manager RAID-5 array structure, each column can

consist of a different number of subdisks. The subdisks in a given column

can be derived from different physical disks. Additional subdisks can be

added to the columns as necessary. Striping (see “Striping (RAID-0)”) is

done by applying the ﬁrst stripe across each subdisk at the top of each

column, then another stripe below that, and so on for the length of the

columns. For each stripe, an equal-sized stripe unit is placed in each

column. With RAID-5, the default stripe unit size is 16 kilobytes.

NOTE Mirroring of RAID-5 volumes is not currently supported.

Left-Symmetric Layout

There are several layouts for data and parity that can be used in the

setup of a RAID-5 array. The Volume Manager implementation of

RAID-5 is the left-symmetric layout. The left-symmetric parity layout

provides optimal performance for both random I/O operations and large

sequential I/O operations. In terms of performance, the layout selection

Column 0 Column 1 Column 2 Column 3

SD SD

SD = Subdisk

Stripe 1

Stripe 2