SATA doesn't use the SCSI command set. It's all still ATA, right down to the inability to abort tasks. (But it is common for operating systems, such as FreeBSD, to model all commands internally as SCSI commands and just translate them to ATA commands if necessary at the last minute.)
SAS HBAs are backwards compatible with SATA drives because they're specifically designed to be. So I guess they're capable of passing either SCSI or, when SATA drives are used, ATA commands.
Where it gets amusing is when you use SAS expanders, since then the link from the HBA to the expander is SAS, but the link from the expander to the drive is SATA. Thus SAS has a special protocol called Serial ATA Tunneling Protocol (STP), which allows ATA to be tunneled over SAS.
What's really comical is that this means if you attached a SATA optical drive to a SAS expander, it follows that you'd be talking SCSI tunneled inside ATA/ATAPI tunneled inside STP over SAS.
The ATA bus is a cut down ISA bus, with some address lines cut. All protocols on it operate in terms of ISA bus transfers, with SATA replacing the physical layer but nothing else.
just to complete the story, SCSI does have ATA command pass through. That is ATA commands over SCSI interface. In Linux, the libata library provides this implementation.
There are SATA drives that understand SCSI over ATAPI albeit in a limited way just to be clear.
>just to complete the story, SCSI does have ATA command pass through.
Very interesting! I just looked it up - it's the ATA PASS-THROUGH command in the SCSI-ATA Translation (SAT) specification. Someone just told me this is apparently a common way to read SMART data from hard drives in USB enclosures.
>There are SATA drives that understand SCSI over ATAPI albeit in a limited way just to be clear.
I assume you mean hard drives. This is extremely interesting. Can you provide more information? Examples of drives, any links?
SAS HBAs are backwards compatible with SATA drives because they're specifically designed to be. So I guess they're capable of passing either SCSI or, when SATA drives are used, ATA commands.
Where it gets amusing is when you use SAS expanders, since then the link from the HBA to the expander is SAS, but the link from the expander to the drive is SATA. Thus SAS has a special protocol called Serial ATA Tunneling Protocol (STP), which allows ATA to be tunneled over SAS.
What's really comical is that this means if you attached a SATA optical drive to a SAS expander, it follows that you'd be talking SCSI tunneled inside ATA/ATAPI tunneled inside STP over SAS.