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

[Tim Freeman]

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