[t13] T10/04-262r0

Jeff Garzik jgarzik at pobox.com
Thu Aug 12 14:59:36 PDT 2004

* From the T10 Reflector (t10 at t10.org), posted by:
* Jeff Garzik <jgarzik at pobox.com>
Curtis Stevens wrote:
> This message is from the T13 list server.
> I agree...
> I think we are getting to the purpose of the CDB transport mechanism at this
> point.  My current vision is manufacturing and maintenance.  This would mean
> that SCSI would be the normal mode of operation for reading and writing the
> media.  However, in the case of a bridged (P/S)ATA device (USB, 1394, SAS,
> etc) you may want to tech support the device by issuing a SMART command.
> Using CDB pass-through, I think this can be done using existing standard
> driver pass-throughs.  It would also allow device failure diagnosis without
> opening the box and removing the ATA device.  Our major use will be for
> vendor specific commands...

> At this point, I do not really see this being used in a performance
> environment.  So, the devices will already have to deal with the SCSI

I agree, and further I think SMART/vendor-reserved/maintenance commands 
will be 99% of the usage of an ATA passthru command.

The fast path will simply be standard SCSI read/write commands, 
translated to ATA commands in the obvious way.

> presentation issue.  The one case I can see is if there are many drives
> presented as one device by the SCSI-ATA bridge.  Then there would need to be
> a mechanism for addressing the individual ATA drives.  I think in this
> environment  (which is starting to look like a RAID), there is a bigger
> problem to solve.

In fact, there are already RAID products on the market that roll their 
own ATA passthru for precisely the reasons stated.  Typically these 
products provide a product-specific method of addressing the individual 
drives outside the scope of the ATA command (CDB) being sent to the 
individual device.


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