VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Understanding VERITAS Volume Manager
Volume Layouts in VxVM
Chapter 1 31
support the full width of a parity stripe. The figure, “Traditional RAID-5
Array,”, shows the row and column arrangement of a traditional RAID-5
array.
Figure 1-22 Traditional RAID-5 Array
This traditional array structure supports growth by adding more rows
per column. Striping is accomplished by applying the first stripe across
the disks in Row 0, then the second stripe across the disks in Row 1, then
the third stripe across the Row 0 disks, and so on. This type of array
requires all disks columns, and rows to be of equal size.
Volume Manager RAID-5 Arrays
The RAID-5 array structure in Volume Manager differs from the
traditional structure. Due to the virtual nature of its disks and other
objects, VxVM does not use rows. Instead, VxVM uses columns consisting
of variable length subdisks (as shown in “Volume ManagerRAID-5
Array,” on page 32). Each subdisk represents a specific area of a disk.
VxVM allows each column of a RAID-5 plex to 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 is implemented by applying the first stripe across
each subdisk at the top of each column, then applying another stripe
below that, and so on for the length of the columns. Equal-sized stripe
Column 0 Column 1 Column 2 Column 3
Row 0
Row 1
Stripe 3
Stripe 2
Stripe 1