[Swift-devel] Swift-issues (PBS+NFS Cluster)

[Ioan Raicu]

I see the numbers, but my instinct says that they can't scale EBS 
performance linearly with every EC2 instance they can start. Perhaps EBS 
is currently underutilized, so much that the EBS servers are relatively 
idle. Once EBS becomes really popular, or if a single large user runs 
EBS to many EC2 instances and runs data intensive workloads, I bet EBS 
performance will start to suffer (in comparison to local disk 
performance). It is certainly an interesting dimension to explore, at 
what scale will local disks outperform EBS.

Ioan

Tim Freeman wrote:
> On Tue, 12 May 2009 15:38:52 -0500
> Tim Freeman <tfreeman at mcs.anl.gov> wrote:
>
>   
>> On Tue, 12 May 2009 15:19:14 -0500
>> Ioan Raicu <iraicu at cs.uchicago.edu> wrote:
>>
>>     
>>> Hi Tim,
>>>
>>> Tim Freeman wrote:
>>>       
>>>> Is that for speed or less moving parts?  I think EBS is the fastest option
>>>> they have for disk space (faster than local disk), fyi.
>>>>
>>>>
>>>>   
>>>>         
>>> Can you elaborate more on how EBS, can be faster than local disk? I know 
>>> nothing about EBS, but there are only 2 ways it can work. Since it is 
>>> persistent, it likely lives on S3 (or something similar). When it is 
>>> mounted, perhaps it still lives remotely, or perhaps it gets copied to a 
>>> local disk, and runs locally. A locally running EBS, should be 
>>> comparable in speed to a raw local disk, perhaps a bit slower for yet 
>>> another layer of abstraction. If EBS lives remotely, perhaps in a 
>>> completely idle EC2 cloud, a remote EBS might perform better than a 
>>> local disk (assuming network communication is lighter-weight than 
>>> SATA/PATA bus operations), but I can't imagine how this can hold true in 
>>> a large scale and loaded cloud scenario, where shared infrastrucutre 
>>> (network, S3, etc) can become congested under load.
>>>
>>> I don't see how EBS can be faster than local disk. Can you elaborate 
>>> more on this claim?
>>>       
>> They state that it is purely network based (they do not list the technologies
>> they use but this could be infiniband, iscsi, etc.).  It's not uncommon to see
>> a SAN etc. faster than a local disk...
>>
>> I made my statements based on Amazon documentation:
>>
>> "The latency and throughput of Amazon EBS volumes is designed to be
>> significantly better than the Amazon EC2 instance stores in nearly all
>> cases." 
>>
>> I just googled and found this person showing that EBS wins on medium and high
>> powered instances (although someone comments at the end that 'dd' tests are
>> not the best thing to measure why EBS is better):
>>
>> http://developer.amazonwebservices.com/connect/message.jspa?messageID=125197
>>     
>
> Also, as I was saying, using RAID can make it even better, found some number
> for that:
>
> http://af-design.com/blog/2009/02/27/amazon-ec2-disk-performance/
>
> Tim
>
>   

-- 
===================================================
Ioan Raicu, Ph.D.
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Distributed Systems Laboratory
Computer Science Department
University of Chicago
1100 E. 58th Street, Ryerson Hall
Chicago, IL 60637
===================================================
Email: iraicu at cs.uchicago.edu
Web:   http://www.cs.uchicago.edu/~iraicu
http://dev.globus.org/wiki/Incubator/Falkon
http://dsl-wiki.cs.uchicago.edu/index.php/Main_Page
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