SORT BY:

LIST ORDER
THREAD
AUTHOR
SUBJECT


SEARCH

IPS HOME


    [Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

    Re: iscsi : changes involving tgt portal group tag.



    Apologies for the late followup, but this discussion has me puzzled.
    
    Part of the concern appears to be around the worry that an initiator
    might reconnect to "the wrong" port and as a result end up talking to
    the wrong LU when it issues additional commands to a LUN it knows.
    
    I don't understand how that's possible.  SAM-2 section 4.7.3 shows
    that an LU is a component of a Device (not of a Port).  And 4.8 says
    that a LUN "identifies the logical unit within a SCSI target device".
    
    In other words, no matter what port you use to access a device, a
    given LUN identifies the same LU in that device.
    
    As for the rule in SAM-2 section 4.7.7 that a "port name shall never
    change" and the conclusion that therefore a TPGT must be persistent, I
    would ask "across what scope?" and "how would you tell"?
    
    If I have an iSCSI device that at time T has a port named X, and at
    time T+1 has a port named Y, how would I test whether the proposed
    requirement has been implemented?  I think the answer is: if you can
    see state you created, such as reservation state, but it's now
    attached to a different port name, then that requirement has been
    violated.  Conversely, whenever a target port has no state it needs to
    remember (no reservations, no initiator-specific mode pages (iSCSI
    section 2.4.3.1)) then it can disappear and a new target port can
    appear in its place -- or equivalently, the port can simply change
    its name, you can't tell the difference.
    
    I guess what I'm getting at is this: a requirement for something to be
    persistent has meaning only if there's state attached to that
    persistent thing, state that you can observe.  What exactly is that
    state and long must it be kept?  iSCSI 2.4.3.1 lists some (but it says
    "e.g." so there might be other state?).  Without a complete list of
    that state it's hard to figure out what the correct rule should be.
    
           paul
    
    


Home

Last updated: Tue Mar 12 19:18:08 2002
9076 messages in chronological order