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Date:   Thu, 21 May 2020 00:15:08 +0200
From:   Johannes Hirte <johannes.hirte@datenkhaos.de>
To:     Chris Murphy <lists@colorremedies.com>
Cc:     Zygo Blaxell <ce3g8jdj@umail.furryterror.org>,
        Justin Engwer <justin@mautobu.com>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: I think he's dead, Jim
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On 2020 Mai 20, Chris Murphy wrote:
> On Wed, May 20, 2020 at 3:02 PM Johannes Hirte
> <johannes.hirte@datenkhaos.de> wrote:
> >
> > On 2020 Mai 19, Zygo Blaxell wrote:
> > >
> > > Corollary:  Never use space_cache=v1 with raid5 or raid6 data.
> > > space_cache=v1 puts some metadata (free space cache) in data block
> > > groups, so it violates the "never use raid5 or raid6 for metadata" rule.
> > > space_cache=v2 eliminates this problem by storing the free space tree
> > > in metadata block groups.
> > >
> >
> > This should not be a real problem, as the space-cache can be discarded
> > and rebuild anytime. Or do I miss something?
> 
> The bitmap locations for the free space cache are referred to in the
> extent tree. It's not as trivial update or drop the v1 space cache as
> it is the v2 which is in its own btree.

I still don't see the problem. Free space cache is needed for
performance, not function. If it's not available, this can be
ignored. 

-- 
Regards,
  Johannes Hirte