Tony Travis wrote: > Tomislav Maric wrote: >> Hi everyone, >> >> I've finally gathered all the hardware I need for my home beowulf. I'm >> thinking of setting up RAID 5 for the /home partition (that's where my >> simulation data will be and RAID 1 for the system / partitions without >> the /boot. >> >> 1) Does this sound reasonable? > > Hello, Tomislav. > > So far so good, but RAID5 trades capacity for perfomance... > >> 2) I want to put the /home at the beginning of the disks go get faster >> write/seek speeds, if the partitions are the same, software RAID doesn't >> care where they are? > > Actually, it does - Read about the 'stride' of an ext3 filesystem: > > http://wiki.centos.org/HowTos/Disk_Optimization
OK, thanks, nice to know, I've been reading about it in Tannenbaum's book (this home cluster stuff really made me widen my horizon :) ). I've seen Centos mentioned a lot in connection to HPC, am I making a mistake with 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. > >> 3) I'll leave the /boot partition on one of the 3 disks and it will NOT >> be included in the RAID array, is this ok? > > I think you'd be better off putting your system one one of your three > disks, and making a RAID1 for /home from the other two. This will give > you a perfomance gain because RAID1 writes do not involve generating > parity, and you will decouple disk access between 'system' and /home. > You can backup your system disk to the RAID1, or reinstall if it fails. 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... >> 4) I've read about setting up parallel swaping via priority given to >> swap partitions in fstab, but also how it would be ok to create RAID 1 >> array of swap partitions for the HA of the cluster. What should I choose? > > You're going to have to decide between perfomance and HA: Sorry, you > can't have both with only three disks. I've built systems with four SATA > disks each with five partitions: /boot on ext2, swap on RAID1, / and > /home on RAID5, /backup on RAID5 for much the same reasons you are > considering doing it too. It works, and you do get HA, but performance > is not good. I'm now simplifying and upgrading the systems by fitting a > 3ware 8006-2 hardware RAID1 controller and two extra disks for /, swap > and /backups. I'm using the original four disks with a single partition > now as a software RAID5 for an ext3 /home filesystem using appropriate > 'stride' and directory indexing. > >> I've gone through all the software raid how-tos, FAQs and similar, but >> they are not quite new (date at least 3 years) and there's no reference >> to clusters. Any pointers regarding this? > > One thing you need to bear in mind in relation to HA is that software > RAID does not support hot-swap - That's why I chose the 3ware 8006-2, > which is not very expensive. It doesn't automatically detect new disks > and rebuild the RAID, but it does support hot-swap and has a web GUI: > > http://www.3ware.com/products/serial_ata8000.asp > 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. Best, Tomislav > Bye, > > Tony. _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
