There is often misconception that SCSI/SAS is the only way to go for server systems. While it is true that one can get the highest possible performance using a high end SCSI/SAS system, this is not anymore true for middle and low end SCSI installations. As a matter of fact SATA II was overtaking SCSI thus SAS needed to be invented. Read more to find out what is the right choice for you!

Many years ago PATA systems had many drawbacks, you could have only 2 drives on the same channel and the drives on the same channel couldnt be accessed simultaneously and most systems supported only 4 drives using 2 channels and PATA drives did nott support command queuing etc.  At those old times any SCSI system had advantages over PATA systems. But lets not get stuck at ancient past, technology is changing all the time. SCSI was a good choice in the past, but is it still?

With the invention of SATA II, all the problems of PATA systems have been solved. The SATA II drives support serial access and command queuing and currently work with the same interface speed with SAS drives. As well as man SAS controllers can also accept SATA drives.

As well, the SATA II interface actually gives better performance than SCSI interfaces.  In older SCSI systems like Ultra320 SCSI etc. the system channel has higher bandwidth however this bandwidth is shared between the drives. If you have 8 drives, and if they all work at the same time then probably the bus would get overloaded. SATA II works using point to point connections, thus there is a channel reserved for each drive and it is immune to this deficiency of SCSI systems. This is exactly why SAS was invented, because SATA II was overtaking SCSI.

The only advantage of using SAS drives is that there exists 15K RPM drives for it whereas SATA drive speeds end at 10K RPM. However in modern drives this has very little performance impact, most SATA drives come with insane capacities, even over 1TB, this means that these drives have higher data density on the platters which means that one can read the data faster. As a matter of fact, most 15K RPM SCSI drives are only 30% faster at sequential read than 7.2K RPM SATA II drives. The reason for this is that the disk head goes 1/2 speed over the platters but there is almost double amount of data under the disk head. So as a rule of thum, the larger the drive, the better performance one can get.

With the invention of SATA RAID systems using multiple drives do reduce the performance gap further. Actually, SATA overtook SCSI earlier and with the invention of SAS, SCSI systems went slightly ahead again.

Currently one can create a SATA II RAID system which would give the same performance with a 3 times more expensive SCSI RAID system. If you do not need the absolute highest (slightly higher performance than SATA II) performance at the cost of spending 3 times more then you should go with a SAS system, however otherwise SATA II RAID has the best price performance ratio.