SBC-2 Block Limits proposals

Pat LaVarre LAVARRE at iomega.com
Tue Dec 17 14:39:47 PST 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Pat LaVarre" <LAVARRE at iomega.com>
*
> * optimal transfer length: Transfers that
> exceed this size cause performance to drop
> significantly
>
> * optimal transfer length granularity: Transfers
> not this many multiples of blocks cause performance
> to drop significantly
>
> I do not expect disk drives to find much use for
> these fields.
 
How commonly do disk drives behave badly when
bytes/cdb falls __below__ some optimum?
 
The mechanisms I personally know best run
asymptotically faster as one increases bytes/cdb, but
I haven't looked closely at this for some years now.
 
Write-behind/ read-ahead work to hide this, if left
enabled, but last I checked hosts often try to turn
write-behind off.
 
Pat LaVarre

	-----Original Message----- 
	From: Elliott, Robert (Server Storage) [mailto:Elliott at hp.com] 
	Sent: Tue 12/17/2002 1:45 PM 
	To: t10 at t10.org 
	Cc: 
	Subject: New SES-2 Bypass bits and SBC-2 Block Limits proposals
	
	

	* From the T10 Reflector (t10 at t10.org), posted by:
	* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
	*
	These proposals are now available on http://www.t10.org/new.htm for
	discussion at the next CAP meeting:
	
	03-028r0 SBC-2 Block Limits mode page
	Reports a few properties of volumes created by RAID controllers:
	* maximum transfer length: READs or WRITEs greater than this are
	  rejected with ILLEGAL REQUEST/INVALID FIELD IN CDB
	* optimal transfer length: Transfers that exceed this size cause
	  performance to drop significantly
	* optimal transfer length granularity: Transfers not this many multiples
	  of blocks cause performance to drop significantly
	I do not expect disk drives to find much use for these fields.
	
	
	03-029r0 SES-2 Array Status element bypass status enhancement
	Fixes the element bypass status bits for the Array Status
	  diagnostic page in the same manner they were fixed for the
	  Enclosure Status diagnostic page in 02-251r1.
	
	
	--
	Rob Elliott, elliott at hp.com
	Hewlett-Packard Industry Standard Server Storage Advanced Technology
	https://ecardfile.com/id/RobElliott
	
	
	
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