SORT BY:

LIST ORDER
THREAD
AUTHOR
SUBJECT


SEARCH

IPS HOME


    [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
    >
    >
    >
    
    
    
    


Home

Last updated: Tue Sep 04 01:06:15 2001
6315 messages in chronological order