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Re: Use RAID1 mirror as backup during dist-upgrade?

Reiner Buehl put forth on 1/5/2010 7:27 AM:
> Hi all,
> I have a Debian Etch system that runs on a RAID 1 software raid system.
> now I would like to upgrade it to Lenny by splitting the mirror off and
> keep one mirror as a backup. Alternatively I could add a third disk as a
> second mirror and split off this one.
> If the upgrade works, I then add in the old disk again. If it fails I'd
> like to be able to rebuild the array using the OLD mirror that I kept.
> Does anybody have a more detailed description on how to do this? I know
> I can fail a drive with mdadm, but my understanding is that the data on
> this this drive can't then be used again after that. Is that correct or
> can the bad upgrade disk be failed and then the old disk un-failed? How
> would I tell the system which disk to use? What preparation steps are
> necessary other than making both/all mirrors bootable?

The purpose of RAID implementations is to

A. Prevent data loss due to disk failure
B. In some cases increase disk I/O throughput

RAID was never intended as a file backup mechanism, which it seems is what you
are wanting to use it for in this instance.  Tape, eSATA/USB/firewire disk,
CD/DVD-R, Magneto Optical, USB stick, and other such devices are meant for this
task, along with tar'ing files to remote network storage via ftp/nfs/cifs.

You're standing on the edge of the earth with this method.  I'd dare say few
people have stood where you are standing now.  You may well be better off using
a more traditional and proven method, instead of trying to take the "easy" way
out. ;)


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