[svlug] NAS versus SAN

Emmanuel Mayssat emmanuel_mayssat at lynceantech.com
Thu Oct 22 15:57:21 PDT 2009

I am trying to setup an experiment where
1/ data is collected by 1 machine (writer)
2/ data is processed by another (reader)

X-ray images are collected by X-ray detector (2Meg per image)
We rotate the sample and take another picture (360 images per sample)
To rebuilt 3d model, we need access to all the image files at once!
(ok, the algorithm can be improved, but that's a worse case scenario)

With a NAS (linux NFS over copper Gbit Ethernet) configuration, it takes 
half an hour to rebuild the 3d model.
When the files are on the local disk, it takes 1 minute.

How long will it take with a decent SAN configuration?
In that case, how does SAN disk access compare with local disk access in 
terms of speed?

Is an optical link (FC) faster than copper wire? I guess so, but what 
are common data rate on FC?
InfiniBand can do 10Gbit/s. Therefore most FC must be around 1Gbit/s, 
which is comparable to copper Gbit.
So is error rate/latency larger on copper then on optical links?

Ultimately my users want an instantaneous display of the 3d model. They 
obviously cannot wait 30 minutes to get the results....

I looked at EMC Clariion... that's a ~$10K configuration. But nobody 
went wrong by buying EMC right ?
What about a brocade switch ? Hum...

Emmanuel Mayssat

Nezer Zaidenberg wrote:
> In common production environments you will certainly get much better 
> performance using SAN then NAS.
> This comes from so many reasons but if you want me to sum just the 
> main two..
> 1. most SAN servers have much better hardware then NAS server 
> regardless of protocol (if you compare EMC Celerra to EMC Clariion or 
> Symmatrix for example)
> 2. The protocol and data path is more straightforward and more efficient.
> However there are some NAS boxes that are faster then some SAN boxes.
> Linux is usually used as SAN initiator and not target. (You could 
> built a SAN box on top of Linux. It has been done by commercial 
> companies such as XIV (now bought by IBM))
> Regarding cheapest and minimalist solution...
> what do you try to do?
> if you try to have reach certain performance threshold maybe a NAS 
> will do.
> if you want to have SAN regardless of need or performance maybe you 
> can give up FC completely (and thus no switch etc.) but this will 
> hardly be comparable to real life scenario.
> if you want to simulate commercial SAN environment then you need FC. 
> (I usually find out that people (incorrectly) call the FC director 
> "the SAN")
> If you clarify what you want to achieve maybe I can help you better.
> Regarding experience - I've worked on Open and MF environments using 
> Shark(IBM), Symmetrix and HDS 9970.
> They are all excellent boxes.
> Nezer

More information about the svlug mailing list