[plug] Home Server LVM/RAID stuff

[Trevor Phillips]

On Tue, Aug 19, 2008 at 6:37 PM, Matt Kemner <zombie at penguincare.com.au> wrote:
> On Tue, 19 Aug 2008, quoth Keith Bawden:
>
>> RAID is not a backup solution. It will faithfully let you "sudo rm -Rf /" ;-)
>
> And it won't help you if you have multiple disks die at once, for whatever
> reason.

Yeah, I'm aware there's backup & there's backup. ^_^

I'd considered trying the snapshots as an accident insurance policy,
although they don't seem quite as flexible and robust as I would hope.
Still, for a largely read-only data store, having a few modest
snapshots, maybe 1 every 2 days over 6 days, might do the trick. Not
that a tiny snapshot file will stop a full rm... ^_^

> I had a 7-disk RAID5 array in my home server (an old DEC Prioris)
>
> 3 disks died at the same time.  Even RAID6 would not have helped me there.
>
> Of course I have everything that was "important" on those drives :/

Ouch!

> I now back all the important stuff up to a server at a remote location :)
>
> (with snapshots)
>
> Yay for rsync

Is "the loungeroom" remote enough? ^_^;;;
Maybe I should poke a friend about mutual offsite backups of critical files...

My current hardware redundancy solution consists of sporadic rsyncing
between two disks, that I keep meaning to automate one of these
days... Maybe that would be a simpler solution - switch to LVMs for
flexibility, continue to ignore RAID solutions, and properly implement
a rsync backup.

I've discovered inotify recently, and have been toying with the idea
of using it for sloppy RAID - detect a FS change, and trigger a mirror
just of the changes. Or more likely log changes, then periodically
mirror the changes. More efficient than rsyncing a large quantity of
largely unmodified files.

The idea of rolling daily snapshots has a lot of appeal, though. Are
LVM snapshots smart enough to to be relative to each other, instead of
the main volume? ie; if you had snapshot A, then later B, would a
change to the FS only need to be recorded in B, or would the change be
recorded for both A & B, requiring double the storage?

-- 
Trevor Phillips - http://dortamur.livejournal.com/
"On nights such as this, evil deeds are done. And good deeds, of
course. But mostly evil, on the whole."
 -- (Terry Pratchett, Wyrd Sisters)