Are old SCSI tape drives not all created equal?
Guy Sotomayor Jr
ggs at shiresoft.com
Wed Aug 17 14:11:51 CDT 2016
> On Aug 17, 2016, at 12:01 PM, Maciej W. Rozycki <macro at linux-mips.org> wrote:
> On Wed, 17 Aug 2016, Mouse wrote:
>> SCSI is more than just the physical interface. Traditional SCSI is a
>> parallel interface, with a bunch of signals and grounds. But, layered
>> atop the physical interface, there is also a command/response protocol
>> which is, strictly, independent of the physical layer. (I have seen it
>> said that the SCSI protocol is very similar to both ATAPI and SAS,
>> probably because it influenced their design, though I haven't read
>> enough of any of them to really have a good handle on it myself.)
> I don't know of SAS offhand, however ATAPI is pretty much SCSI over ATA.
> That is really SCSI commands and responses wrapped into the so called ATA
> packets (hence the ATAPI acronym, standing for ATA Packet Interface) which
> are chunks of data sent and retrieved with the ATA data write and read
> commands. The USB storage protocol works similarly as well.
If you *really* want to see how this was screwed up, take a look at
Fibre Channel (which is basically SCSI over an optical Fibre network).
While the commands are standard, you can’t really build a Fibre Channel
configuration without using (a lot) of vendor unique commands. And guess
what? Each vendor has their own set! It’s so bad that each combination
has to be tested (even down to the Fibre channel cards…the commands
they support are not all the same). In other words, just because I have a
working configuration with brand A card, brand C switch and brand E
disk array, does not mean that I can put in a brand B switch and still expect
it all to work. The sad thing is that the industry is/was happy with that.
TTFN - Guy
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