On Sat, 2005-09-10 at 09:16, Lamar Owen wrote:
My question is, what is the opinion of those on the list with experience in this area as to the 'best' method of joining these drives. I would like to be able to lose two or more drives and still have redundancy; I had thought about pairing drives in RAID1's and LVM over the array; and I had thought about a big RAID5. But I don't want to shoot performance through the foot, either.
I don't know about 'best', but I have several machines with 6 drives on one controller configured in RAID1 pairs and don't consider the performance to be a problem. I started this way back in the RH 7.x era and did not use LVM - /boot and / are one one drive set, /home on another and /var on another. It was important on some of them that I could yank any single drive and mount it elsewhere without worrying about the rest of the set. Many of the original drives have been replaced one at a time, often hot-swapped and re-synced after a failure. Some have survived motherboard failures with the whole set swapped into a spare chassis for immediate recovery and a couple of boxes were cloned by swapping every other drive to a new chassis and re-syncing with new partners. Everything except the ability to grab data from a single drive should work the same under LVM. With 12 drives you probably don't want to deal with that many separate partitions.
I think you are going to lose a little potential speed with everything on one channel but raid1 only hurts on writes and doesn't add much CPU hit. And unlike raid5, there is no hit at all when running with a broken drive in the set. I said 'potential' speed because the only time you use the full bus speed is with several drives transferring at the same time. You can arrange this with large files written over raid0 stripes, but in practice with small files being randomly accessed tying the heads together with stripes or raid5 may hurt more than it helps.