Re: Major HDD performance degradation on btrfs receive

[Marc MERLIN <marc@merlins.org>]

On Tue, Feb 23, 2016 at 07:01:52PM +0100, Lionel Bouton wrote:
> Why don't you use autodefrag ? If you have writable snapshots and do
> write to them heavily it would not be a good idea (depending on how
> BTRFS handles this in most cases you would probably either break the
> reflinks or fragment a snapshot to defragment another) but if you only
> have read-only snapshots it may work for you (it does for me).
 
It's not a stupid question, I had issues with autodefrag in the past,
and turned it off, but it's been a good 2 years, so maybe it works well
enough now.

> The only BTRFS filesystems where I disabled autodefrag where Ceph OSDs
> with heavy in-place updates. Another option would have been to mark
> files NoCoW but I didn't want to abandon BTRFS checksumming.

Right. I don't have to worry about COW for virtualbox images there, and
the snapshots are read only (well, my script makes read-write snapshots
too, but I almost never use them. Hopefully their presence isn't a
problem, right?)

Thanks for the suggestion.
Marc
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