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For Fibre Channel tape devices, consider the throughput of the tape device and
the HBA. For example, if you are using third generation LTO drives with rated
performance of 80 MBps, and your backup data streams are able to push the
drives to close to this limit, you might choose to put one or two drives per 2 Gbps
HBA. Do not forget to consider the effect of compression.
It is often difficult to achieve the rated speed of high speed adaptors such as
Gigabit Ethernet and Fibre Channel, no matter what the application. Do not plan
on achieving full rated speed with these cards.
15.5.3 Disk topology
It is desirable to have a single Tivoli Storage Manager volume per disk, be it
database, log, or storage pool. This provides the least contention, allowing each
volume to act independently. This is often difficult as disk sizes get larger and
RAID is insisted upon. It takes discipline to dedicate a 72 GB disk to a small 6 GB
log volume, for example. Use of virtualization technologies such as the IBM
TotalStorage® SAN Volume Controller can assist here, since virtual disks can be
made of any size.
In the case of RAID, there is little choice but to have multiple Tivoli Storage
Manager volumes per logical disk. This is an built-in downside to RAID. Instead
of each disk acting independently, they must all work in unison, limiting
performance.
When using JBOD, placing two storage pool volumes on a single disk will not
result in a degradation, and may provide an improvement in performance. This is
due to the fact that Tivoli Storage Manager writes synchronously to storage pool
volumes, and providing the disk with other work to do increases aggregate
performance.
15.5.4 System memory
The largest use of memory in a Tivoli Storage Manager server is the database
buffer pool. A large buffer pool can improve database performance because
fewer disk I/O is necessary. You should provide enough real memory for an
optimal buffer pool. The buffer pool is adjusted using the BUFPOOLSIZE option,
described in 15.3.1, "Server database and recovery log" on page 498. Set this
option to between 1/8 and 1/2 of real memory.
15.5.5 Network
If possible, use dedicated networks for backup (LAN or SAN) so that other
network traffic is not sharing the same wire as backup data.
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IBM Tivoli Storage Manager Implementation Guide
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