A SAS Outstanding Xfer_RDY Question.

Robert Snively rsnively at Brocade.COM
Tue Jul 1 10:05:04 PDT 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* Robert Snively <rsnively at Brocade.COM>
*
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Based on this note, and the rest of the conversation up 
thru this morning, it looks like First Burst is something that 
should be removed from SAS.  It would certainly provide a notable 
simplification of function. 

Robert Snively 
Brocade Communications Systems, Inc. 
1745 Technology Drive 
San Jose, CA  95110 
E-Mail:         rsnively at brocade.com 
Phone:          (408) 333-8135 
Fax:            (408) 333-6655 


> -----Original Message----- 
> From: Elliott, Robert (Server Storage) [ mailto:elliott at hp.com
 ] 
> Sent: Monday, June 30, 2003 3:47 PM 
> To: Nixon, Bob; t10 at t10.org 
> Subject: RE: A SAS Outstanding Xfer_RDY Question. 
> 
> 
> * From the T10 Reflector (t10 at t10.org), posted by: 
> * "Elliott, Robert (Server Storage)" <elliott at hp.com> 
> * 
> I think the mode page is more than enough for this misplaced feature. 
> 
> First Burst Size is not useful for the low latency 
> environment which SAS 
> is supposed to be.  SAS COMMAND frames are interlocked, requiring 
> waiting for an ACK before sending another frame.  There's not much 
> benefit for the target to send just an ACK after receiving a COMMAND 
> frame rather than send an ACK followed by an XFER_RDY frame.  It's not

> like iSCSI, where the data can be pipelined right behind the command 
> frame because they are likely to be in transit over a very long 
> distance. 
> -- 
> Rob Elliott, elliott at hp.com 
> Hewlett-Packard Industry Standard Server Storage Advanced Technology 
> https://ecardfile.com/id/RobElliott
<https://ecardfile.com/id/RobElliott>  
> * 
> * For T10 Reflector information, send a message with 
> * 'info t10' (no quotes) in the message body to majordomo at t10.org 
> 
> 


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 RE: A SAS Outstanding Xfer_RDY Question. Based on this note, and the rest of the conversation up 
thru this morning, it looks like First Burst is something that 
should be removed from SAS.  It would certainly provide a notable 
simplification of function. Robert Snively 
Brocade Communications Systems, Inc. 
1745 Technology Drive 
San Jose, CA  95110 
E-Mail:         rsnively at brocade.com 
Phone:          (408) 333-8135 
Fax:            (408) 333-6655 
> -----Original Message----- 
> From: Elliott, Robert (Server Storage) [mailto:elliott at hp.com] 
> Sent: Monday, June 30, 2003 3:47 PM 
> To: Nixon, Bob; t10 at t10.org 
> Subject: RE: A SAS Outstanding Xfer_RDY Question. 
> 
> 
> * From the T10 Reflector (t10 at t10.org), posted by: 
> * ;Elliott, Robert (Server Storage); <elliott at hp.com> 
> * 
> I think the mode page is more than enough for this misplaced feature. 
> 
> First Burst Size is not useful for the low latency 
> environment which SAS 
> is supposed to be.  SAS COMMAND frames are interlocked, requiring 
> waiting for an ACK before sending another frame.  There's not much 
> benefit for the target to send just an ACK after receiving a COMMAND 
> frame rather than send an ACK followed by an XFER_RDY frame.  It's not 
> like iSCSI, where the data can be pipelined right behind the command 
> frame because they are likely to be in transit over a very long 
> distance. 
> -- 
> Rob Elliott, elliott at hp.com 
> Hewlett-Packard Industry Standard Server Storage Advanced Technology 
> https://ecardfile.com/id/RobElliott 
> * 
> * For T10 Reflector information, send a message with 
> * 'info t10' (no quotes) in the message body to majordomo at t10.org 
> 
> 
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