So what else is there that differentiates SCSI, (P)ATA, SAS, NL-SAS and SATA?

Size matters

In part 1 we talked about Rotations Per Minute and Command Queuing, but what else is there that makes a certain drive a better choice than any other? Other differences are the size of the platters. Commonly used are 3.5 inch and 2.5 inch. Although it makes sense that smaller platters can rotate faster than larger platters in the end only the size of the drive cage matters. It’s in fact somewhat weird that most 2.5 inch drives now rotate at 10k RPM and the 3.5 inch drives at 15k. Being able to cool the device is probably the main reason why a 10k drive only spins at 10k RPM. If it would rotate any faster, it would heat up more and heat dissipation could become a serious problem. So if you need a high GB per square meter density and performance doesn’t really matter, then the 2.5 inch drives make sense, but if performance is the key differentiator, the more IOps you can squeeze out of each drive, the better. And since we’re not discussing data center designs here, only quality / performance counts.

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Everybody needs storage space nowadays. Whether it is used for high performance computing or simply storing family snapshots, we all need room to store data which is important to us.

In the old days (the 1990s) things were fairly easy: you had either ATA or SCSI. The much older RLL and MFM are now called ancient and therefore not talked about in this article. ATA was mainstream for about 10 years and SCSI was expensive, but also very fast. Both standards used a flatcable and the data was sent to and from the drive in parallel. But when speeds increased the timing of each of the separate signals became difficult and just like cd players in the 1980s manufacturers started using serial lines. This meant that higher speeds could be accomplished and also that the huge flatcables were now traded in for much smaller cable, which improved the airflow as well.

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