Re: iSCSI: problem with LUN discovery

[julian_satran@il.ibm.com]

JP,

Unless I misunderstood you this is entirely a T10 issue.
Presenting a different LU map to each initiator as identified by the port
or the ACCESS-ID is intentional (each initiator can view a different set of
LUs)and part
of the protection mechanisms of SCSI.

With iSCSI at later stages (when we start handling discovery and
management)
the pain of getting to a specific volume might be eased.

Julo

Raghavendra Rao <jpr@divyaroot.India.Sun.COM> on 27/09/2000 23:05:22

Please respond to Raghavendra Rao <jpr@divyaroot.India.Sun.COM>

To:   Julian Satran/Haifa/IBM@IBMIL
cc:
Subject:  iSCSI: problem with LUN discovery





Julian,

Do you agree that following is a problem ? If so, can we fix it ?

  SAM doesn't prohibit a target device from presenting initiator specific
  values for LUs. So it is believed that similar values for a LU may not
  necessarily address the same LU inside a target when accessed from
different
  initiators.

  So the vendor ID page 83 of INQUIRY command is considered to be unique
  for a LU - There is one caveat to this though, that the page 83 values
  could optionally be target port specific. Anyway, if the hosts were to
  use a more persistent values such as page-83 identifier, say after reboot
  or after reconfiguration, it first needs to translate this page-83
identifier
  into a LUN. This can be done by first issuing a REPORT_LUN command to
  LUN 0 and issuing an INQUIRY page-83 command to each LU in the list
  obtained from REPORT_LUN response until a successful match is found.
  An initiator could cache the mapping for future speedier lookups, but
  it still has to linearly probe out all LUs to get the page-83 unique
  identifiers.

  I hate to do this static probing; This problem can be fixed by either

     a) mandating that LUN values are persistent and same for all
        initiators (more unlikely to be accepted)

  OR

     b) introducing a new page code for INQUIRY in which the initiator
        will pass down the page-83 identifier in the parameter list
        to LUN 0 and the target will respond with the LUN corresponding
        to this identifier; Of course, this has to go to T10 for approval.

Thanks.
-JP