Re: Unexpected reset corrupted Reiser4 filesystem

[David Masover <ninja@slaphack.com>]

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Andrew James Wade wrote:
> Hello,
> 
> One of my Reiser4 filesystems was corrupted by a power glitch.

No filesystem can prepare for a power glitch, AFAIK.

> fsck fixed the corruption, but my understanding is that an
> unexpected reset should not have corrupted the filesystem. I

It's my understanding that an unexpected _should_ not have corrupted the
filesystem.  Generally, this means that if we have everything working
the way it's supposed to right up until someone hits the Reset switch,
there _should_ be zero corruption.

Caveats:
1.)  _should_ is not _is_.  Just because the developers can't crash it
doesn't mean it's invulnerable.
2.)  power flicker is different than the power/reset button.  It really
all depends on what your hardware actually does when power is cut, but
most hard drives do some sort of write caching, and some of them make it
impossible to turn that off.

To say more, I'd have to know about the physical mechanics involved, but
even if you could make the system absolutely invulnerable to power loss,
you're still going to lose data (not corrupt -- LOSE) in such an event,
unless you have a battery backup.  Even then, your drive is eventually
going to fail -- so use RAID.  And someone is eventually going to rm -rf
your RAID, or spill coffee on it, or hit it with a
tornado/earthquake/nuke, so have multiple sites and make backups.

That's what it all comes down to -- make backups.  The fact that you
have journalling/transactions/fsck/batteries/RAID is all just to make it
a little less catostrophic when stuff does fail.

> have an image of the corrupted filesystem, is it of any use to
> anyone?

Probably someone, not me.  I don't work here, but I'll bet money that
they are going to ask for something from debugfs.

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