On 03/29/2016 04:35 PM, Nick Fisk wrote:
One thing I picked up on when looking at dm-cache for doing caching with
RBD's is that it wasn't really designed to be used as a writeback cache for
new writes, as in how you would expect a traditional writeback cache to
work. It seems all the policies are designed around the idea that writes go
to cache only if the block is already in the cache (through reads) or its
hot enough to promote. Although there did seem to be some tunables to alter
this behaviour, posts on the mailing list seemed to suggest this wasn't how
it was designed to be used. I'm not sure if this has been addressed since I
last looked at it though.
Depending on if you are trying to accelerate all writes, or just your "hot"
blocks, this may or may not matter. Even <1GB local caches can make a huge
difference to sync writes.
Hi Nick,
Some of the caching policies have changed recently as the team has looked at
different workloads.
Happy to introduce you to them if you want to discuss offline or post comments
over on their list: device-mapper development <dm-devel@xxxxxxxxxx>
thanks!
Ric
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