[Beowulf] RAID for home beowulf
tomislav.maric at gmx.com
Sat Oct 3 15:48:06 PDT 2009
Tony Travis wrote:
> 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:
> I used RH6-9, and Fedora core2, but I switched to Debian and now Ubuntu.
So it can be done. :) Great, I love 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.
OK, thanks, I think I'm getting the hang of this... I guess I'll have to
balance some goals and play around with the configurations.
> 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?
I'm assembling and configuring something like this for the first time
ever. So the answer is: not yet, haven't thought of that, thank you very
much for the advice. :)
>> 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.
I figured it's something like that... hardware RAID will have to wait
for a while, definitely...
> Good luck!
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