For the user who is performance-conscious, who will be doing real multitasking, using many devices at once, doing heavy development work, supporting multiple users at once on the machine, or who otherwise wants the best and is not afraid if it costs a few hundred dollars more, SCSI is the obvious choice. SCSI offers the most flexibility, the most choice of peripherals, and the best performance in a multitasking or multi-user environment.
SCSI is hideously more expensive than SATA, and the difference has only gotten bigger. The things that traditionally gave SCSI an edge (such as SCSI TCQ) have long since been adopted for ATA and SATA (in form of NCQ). While SCSI TCQ has longer queue, in reality the performance benefit from it is minimal.
While SCSI might offer better single drive performance (15kprm drives), the costs of such system compared to nice SATA RAID setup makes SATA more affordable and attractive.
I'm not denying SCSI has it's special uses, but in generic use servers SCSI has been dead for years.
In practice SATA has replaced SCSI in many cases. This is why I consider my argument valid.
ATA drives are cheaper than SCSI or Fibre Channel drives and there's a reason. SCSI and FC drives use a processor for executing the commands and handling the interface and a separate processor controlling the head positioning through servos. ATA drives use a single processor for both which means that if the rotational positioning requires more adjustments due to factors such as rotational vibration or wear, more processor time will be dedicated for that which can affect the performance of the drive. Because of this, you will usually see a lower RPM for the ATA disk drive and also a shorter warranty period. But it is cheaper and can be a very good, economical solution for many environments and applications.
This has absolutely nothing to do with system CPU usage. The actual data is transferred using DMA, and while the drive is busy the CPU is 100% free for other uses.
