SPC-4 question on disconnect-reconnect mode page parameter

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Fri Jan 23 11:01:51 PST 2009

* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
Most people think of the maximum burst size in terms of how long a system
is willing to dedicate bandwidth to a particular task. The time concept is
easier to keep in focus when it is related to bytes transferred, not a
multiple of logical blocks that can vary in size.
	     Bill.Martin at emule						   
	     Sent by:							To 
	     owner-t10 at t10.org	       <t10 at t10.org>			   
				       <Narayan.Ayalasomayajula at emulex.com 
	     01/21/2009 04:46					   Subject 
	     PM 		       SPC-4 question on		   
				       disconnect-reconnect mode page	   
In looking at the disconnect-reconnect mode page in SPC4r17, the definition
The MAXIMUM BURST SIZE field indicates the maximum amount of data that the
target port shall transfer during a
single data transfer operation. This value is expressed in increments of
512 bytes (i.e., a value of one means 512
bytes, two means 1 024 bytes, etc.). The relationship, if any, between data
transfer operations and interconnect
tenancies is defined in the individual SCSI transport protocol standards. A
value of zero specifies there is no limit
on the amount of data transferred per data transfer operation.
This works for devices that formatted for data in multiples of 512 bytes
per block; however, this does not map well for devices that formatted for
Protection information and the block size is 520 bytes.  I understand that
the data transfer length can be easily compared to number of 512 byte
blocks; however, if you want to have a max burst size of 32 blocks that are
520 bytes each then this field does not easily map to the number that you
want because 33 would map to 32.49 520 byte blocks.  Was there any thought
about tying this to the block size that a storage device was formatted for?
Bill Martin
Office of Technology
Industry Standards
916 772-3658
916 765-6875 (Cell)
bill.martin at emulex.com
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