We have tried both - you can see performance gain, but we finally went
toward ceph cache tier. It's much more flexible and gives similar gains
in terms of performance.
Downside to bcache is that you can't use it on a drive that already has
data - only new, clean partitions can be added - and (although I've read
that bcache is quite resiliant) you can not acces raw filesystem once
bcache is added to your partition (data is only accessible through
bcache, so potentially if bcache goes corrupt, your data goes corrupt).
Downside to flashcache is that you can only combine partition on ssd
with another partition on spinning drive, so you have to think ahead
when planning your disc layout, ie.: if you partition your ssd with `n'
partitions so that it can cache your `n' spinning drives, and then you
want to add another spinning drive you either had to have left some
space on the original ssd, or you have to add a new one. And if you have
left some space - it's been just sitting there waiting for a new
spinning drive.
With cache tier you can have your cake and eat it too :) - add/remove
ssd's on demand, and add/remove spinning drives as you wish - just tune
the pool sizes after you change your drive layout.
J
On 07/10/2015 02:07 PM, David Burley wrote:
In a similar direction, one could try using bcache on top of the actual
spinner. Have you tried that, too?
We haven't tried bcache/flashcache/...
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