Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

21Understanding Veritas Volume Manager
How VxVM handles storage management
Disk arrays
Performing I/O to disks is a relatively slow process because disks are physical devices that
require time to move the heads to the correct position on the disk before reading or
writing. If all of the read or write operations are done to individual disks, one at a time, the
read-write time can become unmanageable. Performing these operations on multiple disks
can help to reduce this problem.
A disk array is a collection of physical disks that VxVM can represent to the operating
system as one or more virtual disks or volumes. The volumes created by VxVM look and
act to the operating system like physical disks. Applications that interact with volumes
should work in the same way as with physical disks.
Figure 1-2 illustrates how VxVM represents the disks in a disk array as several volumes to
the operating system.
Data can be spread across several disks within an array to distribute or balance I/O
operations across the disks. Using parallel I/O across multiple disks in this way improves
I/O performance by increasing data transfer speed and overall throughput for the array.
Figure 1-2 How VxVM presents the disks in a disk array as volumes to the operating
system
Multipathed disk arrays
Some disk arrays provide multiple ports to access their disk devices. These ports, coupled
with the host bus adaptor (HBA) controller and any data bus or I/O processor local to the
Disk 4Disk 3Disk 2
Vo l u m e s
Operating system
Physical disks
Veritas Volume Manager
Disk 1