On Mon, Dec 18, 2017 at 1:49 AM, Anand Jain <anand.j...@oracle.com> wrote:

>  Agreed. IMO degraded-raid1-single-chunk is an accidental feature
>  caused by [1], which we should revert back, since..
>    - balance (to raid1 chunk) may fail if FS is near full
>    - recovery (to raid1 chunk) will take more writes as compared
>      to recovery under degraded raid1 chunks


The advantage of writing single chunks when degraded, is in the case
where a missing device returns (is readded, intact). Catching up that
device with the first drive, is a manual but simple invocation of
'btrfs balance start -dconvert=raid1,soft -mconvert=raid1,soft'   The
alternative is a full balance or full scrub. It's pretty tedious for
big arrays.

mdadm uses bitmap=internal for any array larger than 100GB for this
reason, avoiding full resync.

'btrfs sub find' will list all *added* files since an arbitrarily
specified generation; but not deletions.


-- 
Chris Murphy
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