Re: Hardware triple mirror RAID 1?

Previously Odie Ferrous <odie_ferrous@xxxxxxxxxxx> wrote:
tomviolin wrote:

On Mar 5, 4:13 pm, Arno Wagner <m...@xxxxxxxxxxx> wrote:
Any particular reason for triple-mirroring? Double-mirroring
is usually reliable enough.

Good question. Basically, I'm a one-man IT department, and I'd like
to be able to sleep at night.

We recently experienced a failure of our 4-disk (plus two spares) RAID
5 array. One of the drives failed, and while the spare was still
rebuilding, another drive in the array failed, thus trashing the
entire array.

Then, a few months later, our Promise RAID box completely crashed, and
simultaneously our tape backup drive failed. I had to wait over a
week for the replacement tape drive to arrive, and then I had to
restore everything to a new RAID box. Users were NOT happy.

I was extremely unlucky, granted, but I resolved after the most recent
failure to implement the following:

1. Mirrored RAID 1. That way if the RAID card or host system or
whatever fails, any one of the disks in the mirror can be taken out
and the data easily retrieved. You just can't do that with any
striped system.

2. Triple mirrors. That way, in order to suffer a loss of data, all
three drives would have to fail before the spare drive was rebuilt.
Barring catastrophic events (flood, fire) that would precipitate
multiple simultaneous drive failures of this magnitude, the data will
be safe and accessible at all times.

I am also considering locating a backup server on the opposite end of
our concrete and steel industrial building that would mirror the data
at least nightly, so that even if there were an accident that took out
the main server, the data would be safely mirrored elsewhere.

Given the fact that hard drive prices have been dropping, this
solution seems workable to me.

Why not consider Raid 6 with real-time backup? (Backs up files as they
change.)

If his data fits on a single drive, tripple-RAID1 is better, since
it is simpler and he gets three viable, independent copies.
For larger arrays, I agree that RAID 6 is the way to go. I
currently have one 2TB RAID 6 array under Linux software RAID
for 8 months or so, without problems. Speed is fine.

Promise is hardly top-end kit, anyway...

Agreed.

Arno
.

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