End-to-end logical block guard checking question

Holt, Keith kholt at lsil.com
Fri Jan 23 08:44:39 PST 2004


* From the T10 Reflector (t10 at t10.org), posted by:
* "Holt, Keith" <keith.holt at lsil.com>
*
George,
 
I agree that the current wording is kind of confusing.  Taken by itself, the
statement regarding the EMDP bit seems superfluous.  I assume that statement
is there because of the sentence in the first paragraph:  "Protection
information is generated at the application layer and may be checked by any
object along the I_T_L nexus."  I assume that "any object" includes objects
other than the application client and device server.  Is it a given that
objects other than the application client and device server have special
considerations for out of order transfers?  If so, then perhaps the text
should instead read something like the following:
 
"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 by objects other than the application
client and device server may cause false errors because logical blocks may
be transmitted out of order."
 
Keith
 
-- 
Keith Holt 
LSI Logic Storage Systems Inc. 
keith.holt at lsil.com 
316-636-8665 
 

-----Original Message-----
From: George Penokie [mailto:gop at us.ibm.com]
Sent: Friday, January 23, 2004 8:55 AM
To: t10 at t10.org
Subject: End-to-end logical block guard checking question



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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