Mark Hahn wrote: >> It depends on your workload. RAID5 is good for large sequential writes, >> but sucks at small sequential writes because for every write it has to >> do a read to compare parity. > > well, it's bad at small random writes. small _sequential_ writes would > be able to avoid reads for all but the first transaction. > > IMO, raid5 is often unappealing because raid10 avoids the write penalty, > and raid6 is a lot more survivable. ultimately it depends on your taste > in trading off performance, space efficiency, risk.
I can't wrap my mind around the RAID config, because I'm using software RAID: it supports linear mode, and RAID level 0,1,4 or 5. Since it acts as if a partition is a device, this gives me way too much freedom (more to think about). :)) So, maybe the bold question to ask would be: what would be the best RAID config for 3 HDDS and a max 6 node HPC cluster? Should I just use RAID 1 for the system partitions on one disk, and RAID 0 for the simulation data placed on the same partitions on other two disks: after post-processing, the data is gone anyway... and with a good backup strategy, I don't have to worry about RAID0 not recovering from a disk fail... > >>> 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? >> I don't think this will buy you much performance. There probably is a >> measurable difference, but I don't think it's enough to worry about. > > inner tracks are normally about 60% of the speed of outer tracks - > that's for a normal density-optimized disk, not a latency-optimized > (and therefore inherently small) "enterprise" disk. > >>> 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? >> Sure, but /boot is actually trivial to mirror. Just make sure your boot >> loader is on each disk in the mirror and that each disk is partitioned >> identically, and all you have to do if a drive dies is change the device >> you boot off of if a drive dies. > > or better yet, don't bother booting of the local disk. simply make your > head/admin/master server reliable and net-boot. it's likley that nodes > won't be functional without the master server anyway, and net-booting > doesn't mean you can't use the local disk for swap/scratch/... > Well, I want to configure the net boot for all diskless nodes and use the master node and it's RAID for a performance gains with writing CFD simulation data against network communication and to be able to scale more easily. >>> 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? >> Any swapping at all will kill performance. I would get enough RAM to >> make sure you don't swap. > > well, using swap space is harmless as long as you're not actually swapping > _in_ any nontrivial amount. > > unless you have some very extreme parameters (uncheckpointable long jobs, > flakey hardware or power, banking-level reliability expectations), > I wouldn't bother raiding swap. Excellent, thank you very much! Best regards, Tomislav > _______________________________________________ > 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 > _______________________________________________ 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
