•Transfer Size
Transfer size is the overall total size of the SCSI transfer within a single SCSI command. In some operating systems, there is limit set on this. For example, in Microsoft Windows the default transfer size is 64 KB and to increase the overall transfer size above 64 KB in Windows, a registry entry called “MaximumSGList” (associated with the HBA) must be changed. Many modern HBAs already install their drivers with this registry value set appropriately. Check the registry entries.
•Fragmentation
The more fragmented the files are on disk, the more random will be the disk access method, hence the backup will take longer. If your system does have a
•SAN Inter Switch Links
In the switched fabric, SAN Inter Switch Links (ISLs) ensure that SAN connections have sufficient bandwidth to support the backup traffic going through them. Trunk multiple ISLs together where possible.
•2 Gigabit Fibre Channel
Expect no more than 180 MB/s maximum from a single 2 GB/s Fibre Channel connection.
•SCSI Burst Rate
Beware of disk drives quoted as Ultra320; Ultra 320 refers to the burst rate not the sustained rate. The typical sustained rate from a 15K rpm SCSI Ultra320 disk drive is around 80 MB/s for raw sequential I/Os (that is, without file system read overhead).
•SATA Disks
These types of disks are lower cost, lower performance, and lower reliability than the SCSI disk previously listed but are useful for staging backups because they offer high capacity. A typical 7200K rpm SATA disk drive has lower seek times than an equivalent SCSI disk drive, a burst rate of around 150 MB/s, and a sustained transfer rate of around 50 MB/s.
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