VERITAS Volume Manager 4.1 Administrator's Guide

Understanding VERITAS Volume Manager
Volume Layouts in VxVM
Chapter 134
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.
The figure, “Left-Symmetric Layout,” shows a left-symmetric parity
layout with five disks (one per column).
Figure 1-24 Left-Symmetric Layout
For each stripe, data is organized starting to the right of the parity stripe
unit. In the figure, 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.
Each parity stripe unit contains the result of an exclusive OR (XOR)
operation performed on the data in the data stripe units within the same
stripe. If one column’s data is inaccessible due to hardware or software
1 2 3 P0
6 7 P1 4
11 P2 8 9
P3 12 13 14
16 17 18 19
Column
Stripe
Parity Stripe Unit
(Data)
Stripe Unit
0
5
10
15
P4