[Beowulf] Software Raid

[Michael Will]

IMHO software raid outperforms hardware raid
mostly in pure disk-benchmark situations, not so much when
other applications run as well. 

Maybe NFS fileservers are spezialized enough that software
raid performance is not as much off in production as it is
in benchmarking.

The remaining advantage of hardware is still hot-swapping
failed drives without having to shutdown the server.

Michael 

-----Original Message-----
From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org]
On Behalf Of Michael T. Prinkey
Sent: Tuesday, December 13, 2005 1:17 PM
To: Paul
Cc: beowulf at beowulf.org
Subject: Re: [Beowulf] Software Raid


I can tell you from long experience that this is not true.  I have had
software raid/NFS/SMB servers on our clients' LANs serving up terabytes
of home directories to tens of workstations and hundreds of compute
nodes.  
Our experience is that (at least 3ware) hareware raid is significantly
slow than software raid when using the same hardware.  In fact, the
speedup in using the 8-port 3ware SATA drivers in JOBD mode with
Software
RAID5 was about six times faster than using hardware RAID5 on the same
controller.

The CPU needed to do the parity computation is easily supplied by a
single processor system.  Most of our servers our not SMP unless they
are also asked to do something else, like act as the head node to a
cluster.

There are different arguments about whether or not Linux NFS is ready to
serve large numbers of simulateous hosts to which I am not able to
speak, but for 10-100 users with 100s of CPUs, software RAID/NFS/SMB
under Linux seems to work just fine.

Mike Prinkey

On Mon, 12 Dec 2005, 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?
> 
> 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. 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
> 
> Paul Mc Kenna
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