HP StoreEver MSL6480 Tape Library User and Service Guide

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. Therefore, if the average file size is small,
the read performance will be lower.
To determine the average file size, divide the size of the backup by the number of files.
If the average file size is small (64 KB or less), consider using a sequential, image, or block backup
method that backs up the whole hard drive or LUN image instead of individual files. The trade off
for using one of these methods is that you might only be able to restore the entire image instead
of individual files.
NOTE: File fragmentation will also cause excessive drive seeking, which lowers performance,
so ensure that files are regularly defragmented.
File storage system
The file storage system determines the organization of the files on the disks. Using RAID controllers
to spread files over multiple disks can improve performance because some disks can be seeking
while others are reading. Storing files on a single non-RAID disk results in the slowest performance
while storing files on a high-end disk array results in the fastest performance.
Converting standalone disks to RAID can improve performance.
Connection from the backup server to the disk array
The connection between the host server and the disks determines how much data can be transferred
from the disks to the host computer at a time. A connection with insufficient bandwidth cannot
provide enough data for the tape drives to write at full speed. For optimum performance, the
storage subsystem must be able to provide data at the tape drive’s maximum transfer rate.
Backup systems using a lower speed Ethernet network should use multiple network connections.
Backup/archive server
The backup server must have enough RAM and processor power to transfer the files from the disk
to the tape drive, in addition to running the backup or archive software and any other processes.
Check the RAM and processor usage during a backup operation. If they are operating at capacity,
adding RAM or processor capability can improve performance.
Backup/archive software and method
Each backup method has its own impact on performance, depending on how well it can keep
data streaming to the tape drive. In most cases, native applications don’t have the features required
to maximize performance for LTO tape drives. HP recommends using a full-featured backup or
archive application with this library.
File-by-file backup or archive methods provide the best restore performance if you only need to
restore individual files. However, if the average file size is small, file-by-file methods will significantly
reduce performance.
Disk image, flash, or sequential backup methods provide the fastest performance because they
back up an entire disk, partition, or LUN, which minimizes disk seeking. The disadvantage is that
backup and restore operations work on an entire disk, partition, or LUN. You might not be able
to back up a subset of files or restore a single file. If you can restore a single file, the restore process
will be slow.
Database backup performance will vary based on the use model. To improve performance when
backing up data from a database:
• Use specific backup agents for the database.
• Use the latest versions of the databases.
140 Troubleshooting