On 2015-07-10T15:20:23, Jacek Jarosiewicz <jjarosiewicz@xxxxxxxxxxxxx> wrote:
> 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.
Great feedback, too.
So the point about bcache is very valid. But then, a cache layer does
require a lot more tuning and has many more moving parts, requires more
memory, and a more complex ceph setup.
(I was specifically wondering if a bcache could help in front of SMR
drives, actually.)
But it's really useful to know you're seeing similar speed-ups with the
cache tiering.
Regards,
Lars
--
Architect Storage/HA
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Dilip Upmanyu, Graham Norton, HRB 21284 (AG Nürnberg)
"Experience is the name everyone gives to their mistakes." -- Oscar Wilde
_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
