[Beowulf] Software Raid

[Bill Rankin]

On Dec 12, 2005, at 7:26 PM, Paul wrote:

> I read in a post somewhere that it was not possible to use a Linux  
> software RAID configuration for shared file storage in a cluster. I  
> know that it is possible to use software RAID on individual compute  
> nodes but the post stated that software RAID would not support  
> properly support simultaneous accesses on a file server. Is this true?

News to us - we have a fileserver with 2TB of SCSI disks (14 drives)  
serving out NFS to our 450 node cluster.

It's not the fastest solution in the world (see my earlier post  
regarding NFS performance) but it does work.


>
> Assuming that hardware RAID is required (or at least preferable) I  
> was wondering if the built in RAID on some motherboards would be  
> adequate or do we need to look into a dedicated piece of hardware.

It depends - whose "built-in" hardware RAID?  Be aware - some  
"hardware RAIDS" are not full implementations, but rather onboard  
hardware that can support RAID-like operations.  Without the proper  
drives (which often do not exist for Linux) your RAID is simply a JBOD.

> We will have about 10 - 12 cpus initially that will be connected  
> with giganet network. We currently have about a terrabyte of  
> storage space and are planning to mount it using NFS in a RAID 5  
> configuration. Our applications for now will be database intensive  
> bioinformatics apps. I would be very interested in any comments.  
> Thanks

Personally, for that load I would initially go with a simple software  
RAID setup, especially if you are heavy on file reads and light on  
writes.  Do some analysis of your I/O loads once you have everything  
up and *then* determine from there if you need to throw additional  
hardware at the problem.

Good luck,

-bill