HP B6960-96035 User Manual download pdf (Page 72)

Disk performance

All data that Data Protector backs up resides on disks in your systems. Therefore, the

performance of disks directly influences backup performance. A disk is essentially a

sequential device, that is, you can read or write to it, but not both at the same time.

Also, you can read or write one stream of data at a time. Data Protector backs up

filesystems sequentially, to reduce disk head movements. It also restores files

sequentially.

Sometimes this is not visible because the operating system stores most frequently used

data in a cache memory.

Disk fragmentation

Data on a disk is not kept in the logical order that you see when browsing the files

and directories, but is fragmented in small blocks all over the physical disk. Therefore,

to read or write a file, a disk head must move around the whole disk area. Note that

this differs from one operating system to another.

TIP:

Backups are most efficient for large files with little fragmentation.

Compression

If data is compressed on a disk, the Windows operating system first decompresses

the data before sending it across the network. This reduces the backup speed and

uses CPU resources.

Disk image backups

Data Protector also allows you to back up UNIX disks as disk images. With a disk

image backup, a complete image of the disk is backed up without tracking the

filesystem structure. The disk head moves linearly across the surface. Thus a disk

image backup can be considerably faster than a filesystem backup.

Disk Agent performance on Windows systems

Disk Agent performance of Windows filesystem backup can be improved by enabling

asynchronous reading. Asynchronous reading improves performance of the Disk

Agent when backing up data on disk arrays, especially if large files are backed up.

It is recommended to perform test backups to establish if asynchronous reading will

Planning your backup strategy72

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HP B6960-96035 User Manual Page 72