SCSI tape question
Chuck Guzis
cclist at sydex.com
Fri Dec 12 21:41:18 CST 2014
On 12/12/2014 07:24 PM, Jon Elson wrote:
> LOTS of SCSI devices violated the standard protocol in interesting
> ways. My understanding is there are two classes of SCSI drives. One
> class used a scheme that was quite like old 9-track tapes, so that
> there was essentially no formatting that wrapped around the user
> data. So, there would be a physical gap with no magnetic transitions
> between the written user data blocks. There would be a CRC of some
> sort at the end of the user data. Higher-end drives wrapped the user
> data into a more complex format, so each block would have a block
> size and a sequence number at the beginning, and maybe a trailer of
> the same info with the CRC. Often in these systems, there would be
> NO physical gap. This increased data capacity, but made it
> impossible to rewrite a single tape block. The file mark was just a
> special block with minimal or zero-length data packet.
This is a bog-standard 1600 PE density 9 track tape on a 10.5" reel.
So no surprises in the physical format. Just some screwball controller
programming.
--Chuck
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