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HP StorageWorks 1/8 User's And Service Manual: Performance Problems; Average File Size; Performance Impact Of Various File Sizes

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Performance problems

TIP:
For more performance troubleshooting information, see the Performance Troubleshooting Guide at
http://www.hp.com/support/pat.
The process of backing up files goes through many devices, from the files in the file system on the
disk, through the backup server, and out to the Autoloader, all managed by software running on an
operating system. The backup process can only run as fast of the slowest link in this chain.
To find the performance bottlenecks in your system, check the specifications and performance of the:
Average file
File system
Connection from the host server to the
Operating system
Backup
server" on page 124
Backup
type" on page 124
Connection from the host server to the
Media" on page 127
Average file size
The hard drive must seek to the position of a file before it can start reading. The more time the disks
are seeking to files, the lower the performance.
To determine the average file size, divide the size of the backup by the number of files. See the
performance impact of your system's average file size in
Table 27 Performance impact of various file sizes
Average file size
<64 k: small files
64 k – 1 mb: medium
files
118
Troubleshooting
size" on page 118
type" on page 119
configuration" on page 122
Performance impact
POOR. Lots of small files require the disk
to perform many random accesses instead
of a continuous read.
NEUTRAL. Performance accessing
medium-sized files should be okay. The
disks will still need to do a fair number of
random accesses.
disks" on page 119
device" on page 125
Table
27.
Recommendations
If possible, do NOT use a file-by-file
backup method.
For backups with an average file size
<64 k, HP recommends using a se-
quential/image backup that backs up
the hard drive or LUN image instead
of the individual files.
The drawback with the sequential/image
backup method is that you might only be
able to restore the entire disk image and
not individual files. If you can restore
individual files, the restore operation will
be very slow.
No change is necessary but using a
sequential backup method, such as an
image backup, could offer some
performance gains. See above for
drawbacks.

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