On Mon, Nov 22, 2021 at 4:52 PM Nico Schottelius
<nico.schottel...@ungleich.ch> wrote:
>
>
> Peter Lieven <p...@kamp.de> writes:
> > Whatever SSD you choose, look if they support power-loss-protection and 
> > make sure you disable the write cache.
>
> I have read this statement multiple times now, but I am still puzzled by
> the disabling write cache statement. What is wrong with having a (BBU
> based) write cache in front of the SSDs / how does it decrease the
> perfomance?
>
> As far as I can tell, this is just another buffer/cache that is added in
> the write chain and thus should improve speed for small writes. For
> write bursts / longer writes the cache will not play a role anymore.
>
> What am I missing?

This: https://github.com/ceph/ceph/pull/43848/files
https://yourcmc.ru/wiki/Ceph_performance#Drive_cache_is_slowing_you_down

-- dan
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