Installation guide

Configuring Your IP4700 Device for Use with Backup Software
57
Monitoring your Backup Performance
AIT-2 Tape Drive
Performance
The AIT-2 tape drive performance is similar to the DLT7000 tape
drive performance, except that the native throughput for the AIT-2
tape drive is 6 Mbytes per second, increasing to 12 Mbytes per second
with very compressible data.
Disk Performance
The tape drive is often blamed for poor backup performance, when
the root of the problem may actually be the disk. Older disks have
slower transfer rates and slower seek times. Throughput from a client
with such a slow disk may be as low as 1.5 to 2.5 Mbytes per second.
Small Files
Clients that have many small files (50 Kbytes or less) may be unable
to supply data at a good rate. The disk spends more time seeking and
then reading data, and throughput suffers considerably.
Compressibility of
File Data
If data is already compressed, such as pre-compressed image files, the
DLT7000 tape drive cannot further compress the data; thus the
backup rate will slow down to a maximum of 5 Mbytes per second.
Other System
Activity
A client that is busy with other applications cannot supply data for
backup as fast as if only backup was running. The bottleneck could
be disk I/O if there is a lot of other activity, or it could be related to
the CPU. Backup reduces response time of other applications that are
left running while backup occurs.
LAN Throughput
You can expect 40 Mbytes or less per second per Gigabit Ethernet
LAN connection. If the networks used for backup also carry
significant application network traffic at the same time, you will have
less backup throughput than expected. If you want to back up during
a specified time window, consider installing a dedicated backup
network(s).
Session Completion
Session completion occurs when one tape drive runs much longer
than the others. Sometimes this is difficult to determine. The result is
that the total backup time takes longer than you think it should. For
example, the backup may start fine with three sessions on each of
four tape drives. The backup software may show good performance
with 7.5 Mbytes per second on each tape drive. Depending on the
order in which clients finish and new clients start, one client with one