Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

Figure 1-13

Example of spanning

Plex with concatenated subdisks

Data blocks

Subdisks

VM disks

Physical disks

disk01-01

Data in

disk01-01

Data in

disk02-01

disk01-01 disk02-01

disk01

n n+1 n+2 n+3

devname1

n n+1 n+2

devname2

disk01-01

disk02

disk02-02disk02-01

n+3

The blocks n, n+1, n+2 and n+3 (numbered relative to the start of the plex) are

contiguous on the plex, but actually come from two distinct subdisks from two

distinct physical disks.

The remaining free space in the subdisk disk02-02 on VM disk disk02 can be put

to other uses.

Warning: Spanning a plex across multiple disks increases the chance that a disk

failure results in failure of the assigned volume. Use mirroring or RAID-5 to reduce

the risk that a single disk failure results in a volume failure.

Striping (RAID-0)

Striping (RAID-0) is useful if you need large amounts of data written to or read

from physical disks, and performance is important. Striping is also helpful in

balancing the I/O load from multi-user applications across multiple disks. By

using parallel data transfer to and from multiple disks, striping significantly

improves data-access performance.

Striping maps data so that the data is interleaved among two or more physical

disks. A striped plex contains two or more subdisks, spread out over two or more

Understanding Veritas Volume Manager

Volume layouts in VxVM