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

[John Hodrien]

On Sun, 20 Jun 2010, Dave Fisher wrote:

> 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.

So what *has* triggered the failures of your RAID sets?

> 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.

That doesn't sound like a bad idea.

> 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've found LVM to be nothing but a win, with it proving very robust and
flexible.

> 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.

If you're not happy with managing the RAID yourself under linux, have you
considered buying a SOHO NAS box?  A 7 bay NAS with 2Tb disks in RAID6 would
get you 10Tb usable, with cover for any two disks failing.  I'm personally
wouldn't be concerned about the write performance hit.  You'd probably pay
about 2k, and it'd be a straightforward appliance, offering iSCSI or NFS/CIFS
to taste.  Accessed over gigabit, you'd be limited to <100Mbytes/sec, but I'm
not sure that'd be an issue for what you need.

That'd cover the basic storing of the data and providing access to it.
Backups and any extra cover is another matter.  Separating out your different
classes of data is essential if this isn't going to cost you an arm and a leg,
or be inadequate.

jh