Brendan Grant at Microsoft has provided an answer to a question we get about WHS Disk Management fairly often: Why are internal SATA disks identified as SCSI?

Short answer: You’re using a 3rd party driver to control the SATA adapter, which reports itself as a “SCSI” controller.

Long answer:

ATA miniports in Windows (until Vista) had no capability to support more than one outstanding request at a time.  This is because ATA devices were originally able to handle only a single request at a time.  Although native command queuing (NCQ -- multiple outstanding requests) was added to Parallel ATA (PATA), the implementations were so ... diverse ... that supporting them was not possible for Microsoft, thus no support added.

Of course, vendors thought that NCQ was the best thing since sliced bread, since it improved performance of the drives.  Therefore, they used another driver model, that of the SCSI miniport driver, to control their hardware.  It provided the ability to have multiple outstanding requests, therefore enabling NCQ.  Due to the different means of reporting device IDs between SCSI and ATA, however, there were some oddities that resulted.  One of these oddities is that the drive is reported as “SCSI”.  Another oddity is that the SCSI INQUIRY data may not fully match the ATA IDENTIFY DATA, since the identifier fields have different fields of different lengths.

So, you have a 3rd party SATA controller driver, and thus see “SCSI” even though it’s really SATA.

posted on Saturday, June 20, 2009 10:58 AM | Filed Under [ Site Microsoft ]


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