End-to-end logical block guard checking question

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Fri Jan 23 14:24:56 PST 2004


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

While it is true that EMDP allows blocks to be sent out of order, each "out
of order" section will be preceded by a MODIFY DATA POINTER message that
allows the initiator to correctly predict the LBA (i.e., the reference tag)
for every block. Any initiator that sets the EMDP bit and formats the
target to use protection information should be required to correctly figure
this out. If they can't, then they better not set the EMDP bit .. (most
initiators don't set this bit anyway ..).

I don't think there needs to be a statement about possible false error.
There perhaps should be a statement explaining how MODIFY DATA POINTER
message must be accounted for when protection information is in use so that
false errors do not occur.



                                                                                                                                       
                      George Penokie                                                                                                   
                      <gop at us.ibm.com>         To:       t10 at t10.org                                                                   
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In the protection information description in SBC-2 section 4.5.1 Protection
information overview the following statement is made:

If the logical unit is formatted with protection information and the EMDP
bit is set to one in the Disconnect-Reconnect mode page (see SPC-3), then
checking of the logical block reference tag or the logical block guard
within the service delivery subsystem may cause false errors because
logical blocks may be transmitted out of order.

The statement that false errors may occur because blocks may be transmitted
out of order does not apply to the logical block guard as that is a check
of the block itself and does not care what the order of the blocks is.
Although it may be possible that a service delivery subsystem may see data
within a block the is not in the original order that is not how the above
statement reads.

The question is does it make sense to make a statement about the logical
block guard causing false error? Is yes then the reason has to change
because as currently stated it is illogical.

Bye for now,
George Penokie

Dept 2C6  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880





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