Re: iSCSI: problem with LUN discovery

[John Muth <muth@veritas.com>]

Julo,

FYI. Assuming the initiators are running higher level disk 
management S/W like VxVM (VERITAS Volume Manager), this won't
be a problem. VxVM already deals with device paths moving 
around by doing it's disk identification based on the label, 
not the device path.

John Muth
VERITAS Software

julian_satran@il.ibm.com wrote:
> 
> 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