VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager
Volume Manager and RAID-5
Chapter 1 51
is not as critical as the number of columns and the stripe unit size
selection.
The left-symmetric layout stripes both data and parity across columns,
placing the parity in a different column for every stripe of data. The first
parity stripe unit is located in the rightmost column of the first stripe.
Each successive parity stripe unit is located in the next stripe, shifted
left one column from the previous parity stripe unit location. If there are
more stripes than columns, the parity stripe unit placement begins in the
rightmost column again.
Figure 1-17, Left-Symmetric Layout, shows a left-symmetric parity
layout with five disks (one per column).
Figure 1-17 Left-Symmetric Layout
For each stripe, data is organized starting to the right of the parity stripe
unit. In Figure 1-17, Left-Symmetric Layout,, data organization for the
first stripe begins at P0 and continues to stripe units 0-3. Data
organization for the second stripe begins at P1, then continues to stripe
unit 4, and on to stripe units 5-7. Data organization proceeds in this
manner for the remaining stripes.
0 1 2 3 P0
5 6 7 P1 4
10 11 P2 8 9
15 P3 12 13 14
P4 16 17 18 19
Column
Stripe
Parity Stripe Unit
(Data)
Stripe Unit