Data Out residual overflow/underflow handling

Pat LaVarre p.lavarre at
Fri Sep 21 17:14:57 PDT 2012

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@ if you want to read a logical block you need to read it all, not just
part of it.
@ SCSI is called a 'block oriented" interface.
@ initiators should issue a READ CAPACITY as part of discovery
Last time I coded that test case in a Scsi target, not specifically an
iScsi target, must be ten years ago now ...
I let the Initiator read the 512 of 4096 bytes that kept it from crashing
and I reported the Residue.
Initiators careful enough to notice Residue were happy, because my Target
reported the trouble.
Initiators sloppy enough to ignore Residue were happy, because the next
layer of software up the device driver stack got the chance to get its head
straight, rather than having my Consumer Mass Market target returned as
useless by the human who bought it Aftermarket and plugged it in.
As yet me, I'm far too ignorant of iScsi to begin to guess which Target
designs work well there. I'd guess Enterprise folk in particular might make
different choices than won at Aftermarket.
People who advocate Simple choices irrespective of Plug 'n Pray Pressures
definitely would choose to throw a Check Condition and Kcq always.
Signalling trouble in every possible way gives you your best hope of
clueing in the Initiator who was so rude as to neglect the READ CAPACITY

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