[CentOS] Software RAID setup ideas and an apology.

Les Mikesell lesmikesell at gmail.com
Sat Sep 10 17:09:38 UTC 2005

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.

  Les Mikesell
    lesmikesell at gmail.com

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