Chart 7 - Striped Dumps To 35/70 Dlt Tape Drives - Compaq 219700-001 - ProLiant - 1500 White Paper

Compaq Backup and Recovery for Microsoft SQL Server 6.x
drives be combined with other, slower types of tape drives because this will cause the performance of
the DLT drives to be reduced to that of the slowest drive in the set.
Finally, as mentioned in previous sections, the compressability of the data in your database can affect
the performance numbers seen when dumping to tape drives supporting hardware compression. We
have found however, that performance differences due to compression become less apparent as more
DLT drives are striped together to form a single high-speed tape array.
In this section data is sent to multiple 35/70-GB DLT tape drives, using the tape drive striping
functionality of the SQL Server dump database process. The 35/70 DLT offers not only greater
capacity but also greater performance than the 10/20 and 15/30 DLT's; at the start of this chapter we
demonstrated this performance increase to be almost 4x. For these tests, the following changes were
made to the system configuration:
Y
All of the 15/30-GB DLT drives were removed from the system. Four 35/70-GB DLT drives were

attached to two of the Wide-Ultra SCSI-2/P controllers (two drives 'daisy chained' to each
controller) on the secondary PCI bus.
Y
All tape drives are used as part of a single tape device 'stripe set'. Since up to 4 tape drives were

used, the backup_threads parameter was set accordingly, as the SQL Server dump process uses
one thread per device.
Y
Compression was enabled on the tape drives. A database containing data that lends itself

differently to compression could yield throughput somewhat higher or lower than that displayed
below.
Performance was measured using backup sets of 1 to 4 DLT drives. The throughput results are shown
in the following chart, along with certain hardware usage counters:
The increased performance of the 35/70-GB DLT drives results in far fewer drives being required to
achieve the same performance seen with the 15/30-GB DLT's; with only 2 drives the dump throughput
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Chart 7 - Striped Dumps to 35/70 DLT Tape Drives

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