Re: Performance results with exofs

[sfaibish <sfaibish@emc.com>]

Problem solved; I sent Bruce 2 relevant papers from CMU and FAST 2009.

/Sorin


On Tue, 08 Jun 2010 02:54:53 -0400, Benny Halevy <bhalevy@panasas.com>  
wrote:

> On 2010-06-07 21:49, J. Bruce Fields wrote:
>> On Mon, Jun 07, 2010 at 09:41:29PM +0300, Boaz Harrosh wrote:
>>> On 06/07/2010 09:29 PM, J. Bruce Fields wrote:
>>>>>> On 06/07/2010 07:07 PM, Boaz Harrosh wrote:
>>>>>>> I did not yet publish the Document. It's stuck behind my  
>>>>>>> dis-talent for
>>>>>>> writing and the pnfs bugs de jur.
>>>>
>>>> Untalented writing we can fix, as long as the details are there!
>>>>
>>>>>>>
>>>>>>> Basically all machines:
>>>>>>> - connected by a 1 GBit link.
>>>>>>> - All clients doing a dd write of 8GB file from /dev/zero
>>>>>>> - 3of8 is the special raid-groups arrangement of exofs && objlayout
>>>>>>>   where out of 8 devices each file is striped over 3 devices in a
>>>>>>>   round robin fashion. (*With a small dirty trick)
>>>>
>>>> Random stupid questions:
>>>>
>>>> 	- why do you think the 3of8 arrangement is scaling better than
>>>> 	  the 8of8?
>>>
>>> It's a know problem with a network storage cluster. What happens is
>>> that with 8of8 all the clients exercise all of the nodes at the same
>>> time so they are clashing on the network.
>>
>> OK, so if two clients are both trying to send a stripe of data to the
>> same OSD data at the same time, absent a switch that could somehow
>> afford to queue up a full stripe-unit's worth of data, packets get lost?
>>
>> (Also, out of curiosity: do you know of any papers or documentation that
>> describe that problem in more detail?)
>>
>
> A good place to start would be
> http://www.pdl.cmu.edu/Incast/
>
> Benny
>
>> --b.
>> --
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>



-- 
Best Regards

Sorin Faibish
Corporate Distinguished Engineer
Network Storage Group

         EMC²
where information lives

Phone: 508-435-1000 x 48545
Cellphone: 617-510-0422
Email : sfaibish@emc.com