iSCSI:SCSI Mode Pages

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Tue Sep 18 15:24:54 PDT 2001


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*

The bit is intended to allow targets to send Modify Data pointer messages,
which is the only mechanism to allow transmitting data out of order. Data
that is not in order is required to be preceded with this message, which
contains an offset to the data pointer to indicate where in the data stream
the chunk of data belongs. This feature is considered a pain to implement
and ususally isn't supported on most devices anyway.

If you still think you want to try this out, generally the Logical Unit is
required to buffer the data and rearrange it as needed (it may not need to
rearrange the data, it will probably rearrange the transfer to/from media
activity to get it organized right).





"Sanjeev Bhagat \(TRIPACE/Zoetermeer\)" <iscsi_t10 at sanjeevbhagat.com>
@t10.org on 09/18/2001 01:30:03 PM

Sent by:  owner-t10 at t10.org


To:   "IPS Refelctor" <ips at ece.cmu.edu>, "T10 Reflector" <t10 at t10.org>
cc:

Subject:  iSCSI:SCSI Mode Pages


* From the T10 Reflector (t10 at t10.org), posted by:
* "Sanjeev Bhagat \(TRIPACE/Zoetermeer\)" <iscsi_t10 at sanjeevbhagat.com>
*
I have a query regarding section 3.1.2 EMDP mode parameter. Current text
says

3.1.2 E - Enable Modify Data Pointers Bit (EMDP)


......

If EMDP is set to 1, Data PDU sequences may be transferred in any order. If
EMDP is set to 0, Data PDU sequences MUST be transferred using continuously
increasing offsets.


Does this line mean that if EMDP=1 the out of order received data PDUs by
the iSCSI target be transferred directly to the actual SCSI LU (say a HDD)

or

does it mean that the if EMDP=1 the out of order received data PDUs be
stored in some external buffer provided by SCSI LU and re-assembled and
ordered there before transferring it into the SCSI LU.

Regards,

Sanjeev


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