Re: iSCSI: frame formats

[Stephen Bailey <steph@cs.uchicago.edu>]

Julian,

> Read10 and Write10 can still be accomodated with several data PDUs as we
> maintained the total read/write count (expected data) as a 32 bit field.
> It is only the individual PDU that went down to 16M.

I realize that.  I said that Read10 could not be accommodated within a
SINGLE PDU.

I know the endpoints CAN tile the data into sequences of PDUs of
arbitrarily small size.  The question is whether they WANT to do that.
My endpoints don't.  It boils down to whether you want to tile iSCSI
PDUs in hardware or not.  If you use something like an RDMA layer to
do your data handling, it's better not to add an additional ULP tiling
requirement.  You want to have the protocol support arbitrarily large
(within some expansive limit like 2^32) PDUs.

> It is worth noticing also that the CRCs we are contemplating have a
> guaranteed haming distance of 4 for blocklengths of less than 2^31 bits.

Understood.  Yet another reason to insert integrity below iSCSI.
Disabling CRC is presently supported, so I'm not worried about the
CRCs.

Steph