Determining application client support for CRN.

Santosh Rao santoshr at
Mon Sep 24 17:56:55 PDT 2001

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* Santosh Rao <santoshr at>
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Hi All,

I've got some questions on the CRN field as defined in SAM-2 Rev 20
Section 5.1 and the EPDC bit in the LUN Control Mode Page in FCP-2. Your
responses would be much appreciated.

   * Is the CRN support capability of the application client to be
     assumed by the device server ? If not, is'nt a bit required in the
     "Control Mode Page" or some other ULP specific mode page to test
     for CRN support at the device server ?

   * What is the intent of the EPDC( Enable Precise Delivery Checking)
     bit in the LUN Control Mode Page in FCP-2 ? I assume this is meant
     to test for the CRN support at the target FCP layer [since
     FCP implementations would treat the CRN byte as reserved in the
     FCP_CMD IU]. I assume this is NOT meant to verify the application
     client support, is that correct ?

   * Is there any need for new SCSI transports to have a bit similar to
     the EPDC bit of FCP-2, if they are guaranteed to support the CRN
     field in their SCSI Command encapsulation IUs from their initial
     revs ? I ask this in the context of iscsi. I also noticed that SRP
     has chosen not to define the Protocol Specific LUN Page [which
     would have contained something equivalent to the EPDC bit].


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