Determining application client support for CRN.

Santosh Rao santoshr at
Tue Sep 25 10:52:12 PDT 2001

* From the T10 Reflector (t10 at, posted by:
* Santosh Rao <santoshr at>
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Dave Peterson wrote:

> CRN at the application client is optional, thus CRN support is not to be
> "assumed" by the device server.
> Application client determines support (or non-support) of CRN at the device
> server via the EPDC bit in the logical unit control page. The application
> enables precise delivery (i.e. CRN) by successfully setting the EPDC bit to
> one.
> The application client is then allowed to use the CRN field as specified in
> FCP-2 clause 4.3


If the "EPDC" bit determines the CRN support in the device server, why is this
bit placed in a protocol specific mode page (LUN Control Mode page. a.k.a.
Protocol Specific LUN Page) and not in a SCSI ULP mode page such as the
"Control Mode Page" ?

My initial thoughts were that the EPDC was only placed in a FCP-2 specific mode
page to verify the target FCP layer's (target SCSI LLP) ability to handle the
CRN in its FCP_CMD IU and had nothing to do with the application client. (which
belongs to the target SCSI ULP).


> <* 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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