Quote:
I found this set of instructions that I'm using as a loose guide for this:

http://www.debian-administration.org/articles/512


Somebody PM'd me this week, asking why that article designated one "drive" as a "hot spare" in a RAID1 array.

I very much prefer such questions to be asked in the forums/threads, like now, rather than in PM -- because this way everyone gets to see the question and contribute to the answers, and it's all nice and searchable afterward.

So, back to the question: why a "hot spare" for RAID1? Well, normally that would not make much sense to most people, as the entire concept of RAID1 is a bunch of "hot spares" kept up-to-date in parallel. But in this case, the RAID1 was just a small partition of each drive, and the bulk of the space was in a RAID5 array. A "hot spare" makes good sense for RAID5, and so that's why they did it that way.

The idea is that when a RAID5 drive fails, the system suddenly has no redundancy, so it becomes imperative to configure/update a new drive immediately --> the hot spare.

And since that article was treating all drives more or less the same, they decided to "hot spare" the RAID1 partition of that same drive for consistency. So that the drive could be removed/replaced/whatever at any time without impacting either of the two RAIDs.

There's also a typo in that article, where in the section dealing with RAID5 they accidently use "RAID1" in one of the instructions:

    Now you will want to choose Create MD device again.

    * Multidisk device type: RAID5
    * Number of active devices for the RAID5 array: 3
    * Number of spare devices for the Raid1 array: 1

Cheers


Edited by mlord (24/08/2007 10:54)