We’ve reviewed how physics and the manufacturers’ practices of generalization both negatively impact a hard drive’s speed. Today we are discussing how the interconnect mode impacts the hard drive performance.
So we’ve all heard: fast drives are SAS, slow drives are SATA. Normally, you see this backed with SAS drives being 10-15k and SATA drives being 7.2k, but there are SAS drives at 7.2k and SATA drives at 10k. SAS itself is not faster on its own, it’s just an interconnect.
SAS (Serial Attached SCSI [Small Computer System Interface]) is nearly identical to the SCSI drives that we’ve used for 25 years in servers; the only difference is that the same commands are now passed serially over a different, higher bandwidth medium. SATA (Serial attached ATA) is nearly identical to the ATA drives (IDE) that we’ve used for 25 years in desktops, except again, it’s over a different medium.
However, these two mediums are now inter-operable, which causes people to think that the two technologies are basically the same when they aren’t. SCSI was made to support multiple devices on a single bus, whereas ATA was made for a very few devices on a bus. Because of this, ATA does not play well with others, and does not accept commands from multiple places very well.
There have been advances to optimize things over the years, but it is only glossing over the issue that the ATA protocol is inferior in multiple device environments to the SCSI protocol. If there are only two or three drives, the issue may be negligible. If there are five, 10, or 100 drives, then the issue can have a HUGE impact on performance.