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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iSCSI: Why is ACA optional?Charles, It is good enough if it is mandated for new devices - those are likely to appear with native iSCSI - with a wording in the SHOULD class (strongly recomended). Regards, Julo Charles Monia <cmonia@NishanSystems.com> on 30/11/2000 21:29:45 Please respond to Charles Monia <cmonia@NishanSystems.com> To: Julian Satran/Haifa/IBM@IBMIL, ips@ece.cmu.edu cc: Subject: RE: iSCSI: Why is ACA optional? Hi Julo: A blanket requirement for mandatory ACA support would make almost all legacy devices noncompliant. I don't think the T10 community would be willing to support that any time soon. Charles > -----Original Message----- > From: julian_satran@il.ibm.com [mailto:julian_satran@il.ibm.com] > Sent: Wednesday, November 29, 2000 9:21 PM > To: ips@ece.cmu.edu > Subject: RE: iSCSI: Why is ACA optional? > > > > > Charles, > > That is probably the path we should be taking although I > wonder why would > T10 not mandate as it > as this thing affects all interconnects. We might then (as > with the name > mapping) see it happen in T10. > > Regards, > Julo > > Charles Monia <cmonia@NishanSystems.com> on 30/11/2000 00:06:29 > > Please respond to Charles Monia <cmonia@NishanSystems.com> > > To: "Ips (E-mail)" <ips@ece.cmu.edu> > cc: > Subject: RE: iSCSI: Why is ACA optional? > > > > > Hi Julo: > > > > > -----Original Message----- > > From: julian_satran@il.ibm.com [mailto:julian_satran@il.ibm.com] > > Sent: Wednesday, November 29, 2000 11:18 AM > > To: ENDL_TX@computer.org > > Cc: ips@ece.cmu.edu > > Subject: Re: iSCSI: Why is ACA optional? > > > > > > > > > > Ralph, > > > > That is an interesting argument. > > > > However, now that disks have become more complex and can > > queue tasks how > > would you > > handle having one task rejected because the queue was full > > and the next > > (still in flight) accepted because > > some slot became available? > > > > The case you mention certainly addresses most but not all > such occurences. > There are other transient exceptions, such as commands that > terminate with > a > BUSY or ACA ACTIVE status, that have the same effect but do > not themselves > result in an ACA condition. > > > And this might even happen inside the host (possibly a large > > SMP) that with > > SMP would not have to care coordinating tasks but without ACA > > will have to > > strictly serialize access. > > > > IMHO TODAY not mandating ACA is a mistake (IBM 360 disk > > controllers had it > > 30 years ago for the very reason I quoted). > > I any case iSCSI can do little to ease the pain - except to > > point out to > > those that plan using disk subsystems without ACA to rely on status > > numbering and issue commands one by one. > > > > I believe iSCSI always has the option of making ACA support > mandatory (in > the same way that autosense support is mandatory). If so, > for practical > reasons it will be up to the initiator's iSCSI stack to do so > in a way that > is transparent to the parts of the I/O driver stack above the > iSCSI layer. > > Charles > > >
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