Tomislav Maric wrote:
[...]
I've seen Centos mentioned a lot in connection to HPC, am I making a
mistake with Ubuntu??
Hello, Tomislav.
[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:
http://ubuntuforums.org/showthread.php?t=1030849
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:
http://www.baarf.com/
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
and performance.
Good luck!
Tony.
--
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.tra...@abdn.ac.uk, http://bioinformatics.rri.sari.ac.uk/~ajt
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