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Performance Considerations for Tape Drives and Libraries
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Figure 1-7. Bottlenecked Data Flow vs. Load-Balanced Disk Array
Finally, FC disk arrays on the SAN can also experience the same performance limiters described in
"Hard Drive and RAID Array Configuration." Therefore, improving the performance characteristics
of the disk arrays will also have a direct effect on backup speed across the SAN.
SAN Configurations Utilizing the Library Fibre Channel Bridge
Certain tape libraries may be connected to a SAN by way of a Fibre Channel bridge module. The
module acts as a bridge between the SCSI and FC protocols and provides additional management,
security, and operational features unavailable in most native FC libraries. For details on these
features, see the Fibre Channel bridge User's Guide for your tape library.
In some tape library configurations, the Fibre Channel bridge module may act as a bottleneck and
decrease performance of tape drives. This is because the processing capability in the Fibre Channel
bridge module required to bridge the SCSI and FC communication cannot meet the aggregate
data throughput offered by certain multidrive configurations. Despite this, most data backup
solutions will not experience the Fibre Channel bridge module as the primary limiting factor in
tape performance. Dedicated backup servers will frequently encounter a situation where the
limitations at the host will be compounded by the exertion of feeding data to multiple tape drives.
This results in average drive performance below the level where the Fibre Channel bridge module
becomes a factor.
Fibre Channel
Switch
Fibre Channel
Switch
HOST
HOST
Fibre Channel
Switch
Fibre Channel
Switch
Fibre Channel
Disk Array
Fibre Channel
Disk Array
Tape Library Tape Library