On 2017-11-02 11:02, Martin Raiber wrote:
Hi,
snapshot cleanup is a little slow in my case (50TB volume). Would it
help to have multiple btrfs-cleaner threads? The block layer underneath
would have higher throughput with more simultaneous read/write requests.
I think a bigger impact would be proper parallelization of IO requests.
Right now, writes are serialized (they first get sent to one device,
then the next, then the next, until they've been sent to all devices),
and reads aren't inherently load-balanced across devices (ideally, other
things than load, like where the last read came from on a rotational
device, would be factored in, but even just regular load balancing would
be an improvement right now). As a result, multi-device BTRFS volumes
in general don't perform as well as possible, which is then compounded
by other issues (such as snapshot cleanup being somewhat expensive).
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