End-to-end logical block guard checking question

Robert Snively rsnively at Brocade.COM
Fri Jan 23 09:13:02 PST 2004


* From the T10 Reflector (t10 at t10.org), posted by:
* "Robert Snively" <rsnively at Brocade.COM>
*
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George is right.
=20
Perhaps wording like this might help.
=20
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. requires the
service delivery subsystem to be aware that data pointer modifications
may not occur on block boundaries.

This makes it pretty clear that you either have to have a very clever
service delivery subsystem or you have to avoid use of the modify data
pointers capability.
=20
Bob

-----Original Message-----
From: George Penokie [mailto:gop at us.ibm.com]
Sent: Friday, January 23, 2004 6:55 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:=20

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.=20

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.=20

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.  =20

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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 George=20 is right.
  
 Perhaps wording like this might help.
  
 If the logical unit is formatted with protection = information and=20 the EMDP bit is set to one in the Disconnect-Reconnect mode page (see = SPC-3),=20 then checking of the logical block reference tag or the logical block = guard=20 within the service delivery subsystem may = cause false=20 errors because logical blocks may be transmitted out of order. requires = the service=20 delivery subsystem to be aware that data pointer modifications may not = occur on=20 block boundaries.

 This=20 makes it pretty clear that you either have to have a very clever = service=20 delivery subsystem or you have to avoid use of the modify data pointers = capability.
  
 Bob
 -----Original Message-----
From: George Penokie=20 [mailto:gop at us.ibm.com]
Sent: Friday, January 23, 2004 6:55 = AM
To: t10 at t10.org
Subject: End-to-end logical = block guard=20 checking question



In the=20 protection information description in SBC-2 section 4.5.1 Protection=20 information overview the following statement is made: = 

If the logical unit is formatted with = protection=20 information and the EMDP bit is set to one in the = Disconnect-Reconnect mode=20 page (see SPC-3), then checking of the logical block reference tag or = the=20 logical block guard within the service delivery subsystem may cause = false=20 errors because logical blocks may be transmitted out of order. = 

The statement that false = errors may occur=20 because blocks may be transmitted out of order does not apply to the = logical=20 block guard as that is a check of the block itself and does not care = what the=20 order of the blocks is. Although it may be possible that a service = delivery=20 subsystem may see data within a block the is not in the original = order that is=20 not how the above statement reads. 

The question is does it make sense to make a statement about = the=20 logical block guard causing false error? Is yes then the reason has = to change=20 because as currently stated it is illogical.   

Bye for now,
George = Penokie

Dept 2C6=20  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:=20  553-5208
External: 507-253-5208   FAX:=20 507-253-2880



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