[Wylug-discuss] Help needed with 'failed' Linux software RAID 10

[Dave Fisher]

On 19 June 2010 22:25, Chris Davies <chris at roaima.co.uk> wrote:
> I've been on holiday recently. Are you still having RAID/LVM problems?

Well, no and yes :-)

After nearly two weeks of the trauma I got the data back (big thanks
to Tim Fletcher), but had to cannibalise 3 PCs to do it, while wasting
a lot of time and fair bit of cash.

Now most of the data are sitting unused in discs on bookshelves ...
until I figure out a sensible new file server and backup system ....
which is why I still have a RAID/LVM problem ... and why I need to
compress a lot of videos quickly ;-)

The biggest problem is that my confidence in Linux RAID + LVM has been
dented. I've now had 3 RAID failures in two years with not one single
bad block on any of the disks. Moreover, because I've been using LVM
to span filesystems over multiple disks, making a copy of a single
filesystem (in order to tinker with the copy) can take days or even
weeks. On the other hand, neither ZFS (transition cost) nor BTRFS
(immaturity) are practical alternatives right now.

In one respect, my RAID-10 layout did exactly what it was supposed to
do, insofar as it allowed me to recover 100% of the data when 3 out of
the 5 discs in the array had apparently 'failed'. So that will
probably stay in the mix.

I'm now thinking about an external full system mirror, but keeping the
vital and regularly changing data on small single-disc (RAID-10)
volumes. While only using LVM to span discs for essentially low value
archival stuff like videos. The idea being that, in the case of
complete system failure, I can still access the archival material
(mounted read-only) from the backup mirror, without worrying so much
about the absence of a third (insurance) copy while I'm trying to
recover/restore the original files.  The high value stuff will have
both more redundancy on both sides of the mirror and more backup
copies elsewhere.

I am not sure whether I'll keep LVM on the single disc volumes. The
snapshot stuff would be 'nice to have', but I've very rarely used it
to date.

I'd be interested to hear your thoughts on how to manage roughly
6-10TB of data in a home office set-up.  Broadly speaking, I have
about 2 GB of business-critical data, 10-20GB+ of system files and
important databases, while most of the rest is multimedia (I don't
'do' plastic platters any more). Although the chances are that 'the
rest' also includes a few GBs of high value files that got misfiled or
simply forgotten.

Dave