SPC-4 question on disconnect-reconnect mode page parameter

Kevin D Butt kdbutt at us.ibm.com
Wed Jan 21 15:50:32 PST 2009


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Bill,
Maximum burst size is just that, the maximum burst size.  You will need to 
report one 512 byte increment higher but only transfer the 520 bytes.
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/ 
From:
Bill.Martin at emulex.com
To:
<t10 at t10.org>
Cc:
<Narayan.Ayalasomayajula at emulex.com>
Date:
01/21/2009 04:35 PM
Subject:
SPC-4 question on disconnect-reconnect mode page parameter
In looking at the disconnect-reconnect mode page in SPC4r17, the 
definition for the MAXIMUM BURST SIZE is:
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?
Thanks,
Bill Martin
Emulex
Office of Technology
Industry Standards
916 772-3658
916 765-6875 (Cell)
bill.martin at emulex.com



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