Re: What is the vision for btrfs fs repair?

[Duncan <1i5t5.duncan@cox.net>]

On Thu, 9 Oct 2014 12:55:50 +0100
Hugo Mills <hugo@carfax.org.uk> wrote:

> On Thu, Oct 09, 2014 at 11:53:23AM +0000, Duncan wrote:
> > Austin S Hemmelgarn posted on Thu, 09 Oct 2014 07:29:23 -0400 as
> > excerpted:
> > 
> > > Also, you should be running btrfs scrub regularly to correct
> > > bit-rot and force remapping of blocks with read errors.  While
> > > BTRFS technically handles both transparently on reads, it only
> > > corrects thing on disk when you do a scrub.
> > 
> > AFAIK that isn't quite correct.  Currently, the number of copies is 
> > limited to two, meaning if one of the two is bad, there's a 50%
> > chance of btrfs reading the good one on first try.
> 
>    Scrub checks both copies, though. It's ordinary reads that don't.

While I believe I was clear in full context (see below), agreed.  I was
talking about normal reads in the above, not scrub, as the full quote
should make clear.  I guess I could have made it clearer in the
immediate context, however.  Thanks.

> > Thus, while btrfs may randomly bump into a bad block and rewrite it
> > with the good copy, scrub is the only way to systematically detect
> > and (if there's a good copy) fix these checksum errors.



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"Every nonfree program has a lord, a master --
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