Virtual SCSI bandwidth

View information about virtual SCSI bandwidth.

I/O bandwidth is the maximum amount of data that can be read or written to a storage device in a unit of time. Bandwidth can be measured from a single thread or from a set of threads running concurrently. Although many customer applications are more sensitive to latency than bandwidth, bandwidth is crucial for many typical operations, such as backing up and restoring persistent data.

The following table compares the results of bandwidth tests for virtual SCSI and physical I/O performance. In the tests, a single thread operates sequentially on a constant file that is 256 MB in size with a Virtual I/O Server running in a dedicated partition. More I/O operations are issued when reading or writing to the file using a small block size as compared to a larger block size. The test was conducted using a storage server with feature code 6239 (type 5704/0625) and a 2-gigabit Fibre Channel adapter attached to one RAID0 LUN that is composed of 5 physical disks from a DS4400 disk system (formerly a FAStT700). The table shows the comparison of measured bandwidth in megabytes per second (MB/s) using virtual SCSI and local attachment for reads with varying block sizes of operations. The difference between virtual I/O and physical I/O in these tests is attributable to the increased latency when using virtual I/O. Because of the larger number of operations, the bandwidth measured with small block sizes is lower than with large block sizes.