SAS-2 rev.15 Missing Sync lost message definition

Samek samek at halstor.com
Thu Dec 18 03:46:10 PST 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* "Samek" <samek at halstor.com>
*
Brian,
Many years of experience taught me, that small probability of the events 
means that they always will happen, and often in the worst possible moments. 
Other protocols send primitives between frames, which facilitate much faster 
recovery from sync loss. More, some of them provide notification to the 
remote transmitter that the receiver is in trouble. SAS doesn't. Instead it 
relays on the ACK timeout from possible hundreds of outstanding frames. This 
means that the recovery is really messy.
Happy Holidays,
Samek
Halstor Inc,
www.halstor.com
----- Original Message ----- 
From: "Day, Brian" <Brian.Day at lsi.com>
To: "Samek" <samek at halstor.com>; "Elliott, Robert (Server Storage)" 
<Elliott at hp.com>; <t10 at t10.org>
Sent: Sunday, December 07, 2008 9:04 PM
Subject: RE: SAS-2 rev.15 Missing Sync lost message definition
>* From the T10 Reflector (t10 at t10.org), posted by:
> * "Day, Brian" <Brian.Day at lsi.com>
> *
> Hello Samek...
>
> I'm not sure I agree with SAS being specified with too infrequent 
> primitives relative to loss of sync.
>
> SAS 2 defines an ALIGN primitive to be sent every 3.4 us (approximately... 
> it is every 128 dwords at 1.5Gbps).
> The DWS Reset Timeout is specified as 1 ms.
>
> So assuming link multiplexxing is not enabled, from the loss of sync 
> (regardless of how often this may occur due a particular system's BER), 
> there are almost 300	ALIGNs permitting a device to recover sync during 
> the DWS Reset Timeout period before it gives up and performs the link 
> reset.
>
>
> Brian Day
> LSI Corporation
>
>
>
> -----Original Message-----
> From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Samek
> Sent: Saturday, December 06, 2008 11:05 AM
> To: Elliott, Robert (Server Storage); t10 at t10.org
> Subject: Re: SAS-2 rev.15 Missing Sync lost message definition
>
> * From the T10 Reflector (t10 at t10.org), posted by:
> * "Samek" <samek at halstor.com>
> *
> In a real life, due to various factors, the loss of sync will be a common 
> occurence and due to the infriquent primitives may cause link resets, 
> which in SAS/SATA cases are really bad. By the way, dword synchronization 
> may happen any time, not only during a speed negotiations.
>
> Samek Mokryn
> President
> HalStor Inc.
> www.halstor.com
>
> ----- Original Message -----
> From: "Elliott, Robert (Server Storage)" <Elliott at hp.com>
> To: <t10 at t10.org>
> Sent: Wednesday, December 03, 2008 2:30 PM
> Subject: RE: SAS-2 rev.15 Missing Sync lost message definition
>
>
>>* From the T10 Reflector (t10 at t10.org), posted by:
>> * "Elliott, Robert (Server Storage)" <Elliott at hp.com>
>> *
>> DWS Lost is the name of a message going to SP, not the SP receiver.
>> They're sent at similar times and possibly could be made identical.
>>
>> Although the SAS standard (like most other serial protocols) only
>> requires a BER of 10^12 (which is one error every 2.77 min per one
>> direction of a physical link at 6 Gbps), a system generating anywhere
>> near those number of errors will have so many other problems it won't
>> be viable.  Dword synchronization mainly just happens once during
>> speed negotiation. Most of the time is spent finding the center of the
>> bits; once done, identifying the dword boundary by finding a comma is 
>> easy.
>>
>>
>>
>> -----Original Message-----
>> From: Samek [mailto:samek at halstor.com]
>> Sent: Tuesday, December 02, 2008 6:13 PM
>> To: Elliott, Robert (Server Storage); t10 at t10.org
>> Subject: Re: SAS-2 rev.15 Missing Sync lost message definition
>>
>> It looks to me that the DWS Lost message does the same job. I can
>> hardly see why there is a need for two.
>> These are however minor problems. I have much bigger problem with the
>> fact that the comma characters are so sparse in the SAS protocol,
>> resulting in a longer time to acquire synchronization, specially in
>> the noisy environment (please note that with a lower bit energy in
>> faster rates the SNR drops dramatically), which may lead to link
>> resets - catastrophic from the performance point of view.
>>
>> Samek Mokryn
>> President
>> HalStor Inc.
>> www.halstor.com
>>
>>
>>
>> ----- Original Message -----
>> From: "Elliott, Robert (Server Storage)" <Elliott at hp.com>
>> To: <t10 at t10.org>
>> Sent: Tuesday, December 02, 2008 11:17 AM
>> Subject: RE: SAS-2 rev.15 Missing Sync lost message definition
>>
>>
>>>* From the T10 Reflector (t10 at t10.org), posted by:
>>> * "Elliott, Robert (Server Storage)" <Elliott at hp.com>
>>> *
>>> The SP receiver detects ALIGNs, TRAIN_DONEs, and Dwords and sends
>>>them as  ALIGN Received, TRAIN_DONE Received, and Dword Received
>>>messages.  See  figure 35 on page 72.
>>>
>>> If dword synchronization has been lost, however, it stops sending
>>> those messages.  SP_DWS tells the SP receiver that dword
>>> synchronization has been lost using the Sync Lost message.	See this 
>>> wording on page 285:
>>>
>>> "The ALIGN Received, Dword Received, and TRAIN_DONE Received messages
>>> are only sent after the SP_DWS state machine has achieved dword
>>> synchronization."
>>>
>>> ________________________________
>>>
>>> From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Samek
>>> Sent: Thursday, November 27, 2008 1:46 PM
>>> To: t10 at t10.org
>>> Subject: SAS-2 rev.15 Missing Sync lost message definition
>>>
>>>
>>> SP_DWS (6.9) defines a Sync Lost message sent by the SP_DWS state
>>> machine to the SP receiver, however there is no definition anywhere
>>> what the SP receiver should do with this message. Any suggestions?
>>>
>>> Happy Thanksgiving
>>>
>>> Samek Mokryn
>>> President
>>> Halstor Inc.
>>> www.halstor.com
>>>
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