[Beowulf] RAID for home beowulf
a.travis at abdn.ac.uk
Sat Oct 3 15:30:39 PDT 2009
Tomislav Maric wrote:
> I've seen Centos mentioned a lot in connection to HPC, am I making a
> mistake with Ubuntu??
[Just let me put my flame-proof trousers on...]
I know a lot of HPC people on this list use RH-based distros, but I use
Ubuntu for HPC and I think it's very good. In fact I started a thread on
the Ubuntu forums about EasyUbuntuClustering:
I used RH6-9, and Fedora core2, but I switched to Debian and now Ubuntu.
>> You also need to be aware that RAID5 is not so good when writing to the
>> disk, because parity has to be calculated and written to the disk. In
>> fact this performance penalty has lead to a campaign against RAID5:
> Okaay. :) There's war going on against it.
This campaign really made me think twice about what I was doing using
RAID5. I lied to you (a bit) because I've bought more 3ware 8006-2's to
put /home on RAID10 for our Beowulf servers. I must admit that hot-swap
is one of the main reasons, but BAARF did come into it as well.
> Yeah, but isn't RAID1 used for disk mirroring? How then would I get any
> speedup? From what I've read so far, data stripping is where I get the
> performance boost when using RAID: there's no real parallel
> writing/seeking applied to single data stream in RAID1...
You don't get a speedup when writing, but you avoid the performance
penalty of writing to RAID5. Writing to a RAID1 is essentially the same
speed as writing to a single disk. However, you do get a performance
benefit when reading from RAID1, and you decouple disk access between
the 'system' disk and /home on the RAID1 if you follow my suggestion.
On COTS motherboards the main bottleneck is the PCI bus anyway, not the
SATA disks. Have you benchmarked the disk i/o performance that your
hardware is capable of?
> Thanks, my only problem is that I've reached my financial limits for my
> home project so I have to work with what I have. :) I'll definitely save
> this e-mail in my "importants" folder.
I set out with similar ideas to yours, but in the end you get what you
pay for. My four-disk software RAID systems work fine and they survive
single disk failures without crashing or losing any data. However, we've
had a couple of near double disk failures so I decided to put the system
and /backups on hardware RAID1 instead. I'm still using software RAID5
for /home, and I think this is a reasonable compromise between cost, HA
Dr. A.J.Travis, University of Aberdeen, Rowett Institute of Nutrition
and Health, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, Scotland, UK
tel +44(0)1224 712751, fax +44(0)1224 716687, http://www.rowett.ac.uk
mailto:a.travis at abdn.ac.uk, http://bioinformatics.rri.sari.ac.uk/~ajt
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