Re: Unexpected reset corrupted Reiser4 filesystem

[John Dong <john.dong@gmail.com>]

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If thse were IDE drives, the IDE writeback cache is probably the bad boy -- 
on FreeBSD 5.x, Soft Updates is virtually broken on IDE drives because they 
simply haven't written all the data they promised the kernel that they had.

On 5/25/05, David Masover <ninja@slaphack.com> wrote:
> 
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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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