Factors affecting performance30
HP restricted
Example: SCSI: Consider an 8 KB transfer at burst rates of 8 MB/s and 1 MB/s.
The fast transfer takes 1 ms, while the slow transfer takes 8 ms. Since
the rest of the command may only take 4–5 ms, the difference of 7 ms
is very significant.
SAS and FC: The SAS link is capable of 3 Gb/s (300 MB/s) whereas
the performance of the FC drive depends on the negotiated link speed
of the host/HBA port, any intermediate switch ports and the drive port.
The ports will negotiate to the highest possible mutually supported
speed, ideally 4 Gb/s (400MB/s), then 2 Gb/s (200MB/s) or as low
as 1 Gb/s (100MB/s).
Disk Subsystem
Performance
The speed and configuration of the disks used will have a significant
impact on the backup speed of the whole system.
Recommendation: Using RAID can have a significant effect on the throughput of the
whole system, by the use of interleaved disk reads. Use more spindles
where possible or a reasonably sized RAID system. More disks means
more throughput.
Note that the Raid level makes a difference to performance. RAID5 will
be slower for writes (restores) than reads (backups). RAID0 and RAID1
are faster but expensive in terms of numbers of spindles required and
not so tolerant to disk failure (RAID0 is particularly intolerant).
File System Efficiency Operating systems vary in the efficiency with which they retrieve files
sequentially for backup applications. Most operating system
development effort is put into speeding up access times within files
rather than file seek times.
Consider using staging technology to stage an image before writing to
tape, particularly with many small files, which will impact performance
due to file accession.
Hardware Configuration If the disk and tape drives are on separate buses, the effective
available bandwidth can be doubled.
Recommendation: Use one HBA for disks, and put the tape drive on a separate bus. It
makes sense to split heavily used FC cards across separate PCI busses
so that they do not contend for PCI bus bandwidth.The more PCI busses
the better.
Host CPU Speed Faster hosts can typically transfer data quicker.
Recommendation: Use as fast a processor as possible for the backup system.
Network Transfer Time If backup involves transferring data over the network, network
performance is often a major bottleneck.
Performance Factor Detail
