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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iSCSI: Out of order commandsPaul, I should have seen this comming. iSCSI assumes that TCP is there to take care of the transport window and the transport window is as large as it should be. However we are talking about the application window. The application has advertize it's own window in addition to the transport windows. With transport having things in order we can avoid having to have a complete or even partial duplicate of the windows. If we allow transport to deliver not in order we have to have them duplicated (or at least the control part - and whatever DMA schemes we put in place won't help). Julo Paul Koning <ni1d@arrl.net> 09-11-01 04:25 Please respond to Paul Koning To: Julian Satran/Haifa/IBM@IBMIL cc: ips@ece.cmu.edu Subject: RE: iSCSI: Out of order commands Excerpt of message (sent 8 November 2001) by Julian Satran: > Ron, > > Targets will most likely advertise a total (command and data) window > larger than they can accommodate on any long haul link. With the current > ordering rules nothing bad will happen. This is a very bad idea. The whole notion of a window is that you advertise what you can handle. You DO NOT, EVER, advertise more than you can handle in the hope that you won't be caught. Long haul links are no excuse. The way you deal with those is by having more buffer capacity, and issuing window increases early enough to keep data flowing. In a window flow control scheme, a target that advertises resources it does not have is defective. This is all VERY old hat. TCP has understood how to do this for ages. In particular, it has always been well understood that you HAVE to have more buffers in order to run at high speed over long delay links. In essence, what you're saying is that we have an application protocol here that is so unusual that it should throw out the lessons of the past 40 years, which have taught us how you construct correct protocols. This makes no sense whatsoever to me. I think the notion of out of order commands on a single connection is somewhat strange, but your reason for opposing it is several order of magnitude stranger. paul
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