[TriLUG] Raid gurus?

[Rick DeNatale]

On 3/15/06, WA Brown <brownwa at ftc-i.net> wrote:
> Thats some of what I need to know. I have been working on the server backup.
> I was wondering if the raid set up would do what I needed. What I am
> thinking is that with Raid1, can I unplug one drive ,then plug in another
> and use that as a backup disk? Will the Raid build the new drive that I put
> in place? I have read a bunch about Raid but it dont answer these questions.
> Or am I thinking wrong?

I think that you are thinking correctly, although it's not completely automatic

First of all, you should get out of the habit of thinking as a disk in
a raid array as a backup disk.  It's really a redundant component
which is used to improve availability.  If you do something stupid
like deleting an important file, it's going to be gone from both of
the raid-1 disks, and unless you have a backup you won't be able to
get it back.

That said, if a drive in the raid-1 array fails, you need to use mdadm
to replace it.  The raid driver should notice that it's failed, If not
you need to use "mdadm --fail" to mark it failed, then "mdadm
--remove" to remove the failed drive from the array, and then "mdadm
--add" to add the new drive to the array, at which time the raid
driver will sync it to the existing good drive.

I've not actually gone through having a drive fail, but when I
converted to raid-1, I basically went through a very similar process.
I first put a single new/unused drive into the raid-1 array, leaving
an empty slot.  I then copied the data from the old drive to the
degraded array, and finally added the old drive to the array which
synched it up.

--
Rick DeNatale

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