> -----Original Message----- > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of > Ric Wheeler > Sent: 29 March 2016 14:40 > To: Nick Fisk <nick@xxxxxxxxxx>; 'Sage Weil' <sage@xxxxxxxxxxxx> > Cc: ceph-users@xxxxxxxxxxxxxx; device-mapper development <dm- > devel@xxxxxxxxxx> > Subject: Re: Local SSD cache for ceph on each compute node. > > 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 Hi Ric, Thanks for the heads up, just from a quick flick through I can see there are now separate read and write promotion thresholds, so I can see just from that it would be a lot more suitable for what I intended. I might try and find some time to give it another test. Nick > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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