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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI : On the subject of R2T and Task Tags.That is taking a narrow view on the capabilities of implementers and protocol analyzer designers. Another viewpoint is have a minimalist design - do no specify what you don't have to! Julo Santosh Rao <santoshr@cup.hp.com> on 11/01/2001 09:20:20 Please respond to Santosh Rao <santoshr@cup.hp.com> To: venkat@rhapsodynetworks.com (Venkat Rangan) cc: dotis@sanlight.net (Douglas Otis), matt_wakeley@agilent.com (Matt Wakeley), ips@ece.cmu.edu (IPS Reflector) Subject: Re: iSCSI : On the subject of R2T and Task Tags. The draft must provide for seperate fields to track the task and the R2T along the lines of RX_ID and SEQ_ID in Fibre Channel. Implementations are free to use them as they please and must use 0xFFFFFFFF as their un-used values in these fields. The advantage of defining the fields explicitly in the header as opposed to allowing targets to vertically encode a portion of the tag field for tracking the R2T is that these standard fields are interpret-able by iSCSI Analyzers and will make debugging and tracking the sequence of the I/O easier than implementation specific vertical encoding into a single field. Merging the 2 into a single field is akin to attempting to merge the OX_ID, SEQ_ID and SEQ_CNT fields of FC into a single field and allowing implementation specific vertical encoding. Standard defined fields make for easier introp verification and debugging. - Santosh > > Doug, > > The draft make should not make any statements about how a target chooses to > assign Target Task Tags. Some may choose to assign it per R2T, others may > choose to assign it per task, based on how they choose to implement the > target. Since the initiator is required to reflect it, I do not believe > there are any interoperability issues. If an implementation wishes to do a > Task-SubTask breakdown, they can choose to partition the 32 bits into > portions that can be used for identifying resources within the target. > > Venkat Rangan > Rhapsody Networks Inc. > http://www.rhapsodynetworks.com > > > -----Original Message----- > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of > Douglas Otis > Sent: Wednesday, January 10, 2001 5:27 PM > To: Matt Wakeley; IPS Reflector > Subject: RE: iSCSI : On the subject of R2T and Task Tags. > > > Matt, > > With independent error checking requiring an additional level of error > handling requesting repeated reads, there could be old responses combined > with the retry from failed data digests. (If requesting overlapped reads are > prohibited, retry is an exception.) Without some means of identifying which > retry phase data is associated, a complete set would be difficult to > confirm. As order of each data portion is not mandated and these transfers > themselves may overlap, byte counts can not reveal completion. Should does > not mean 'must.' > > Doug > > > Pierre Labat wrote: > > > > > I agree that the draft must not impose to the target to have a > > different tag > > > for each R2T (it is up to the target implementation to decide). > > I disagree > > > to impose a unique target tag for the whole IO. It imposes the > > target to do > > > score boarding > > > to know when all the data have been received. Letting the > > possiblility to the > > > target > > > to have one tag per R2T (or add a subtag identifying the R2T as > > proposed Santosh) > > > > > > allows the target to dispense with the score boarding. The > > target knows that all > > > the > > > data has been received when a data PDU with the "F" bit set has > > been received > > > for each R2T. > > > > There is no need to do scoreboarding. Just count the number of bytes > > received. If they all add up, then you've received all the data. > > I for one > > would not rely on a PDU with the "F" bit set. I would want to > > cross check it > > with the correct number of bytes. > > > > > > > > > > Regards, > > > > > > Pierre > > > > > > > > > > > > > -Matt Wakeley > > Agilent Technologies > > > > > -- ################################# Santosh Rao Software Design Engineer, HP, Cupertino. email : santoshr@cup.hp.com Phone : 408-447-3751 #################################
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