> -----Original Message----- > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of > Burkhard Linke > Sent: 20 March 2015 09:09 > To: ceph-users@xxxxxxxxxxxxxx > Subject: Re: OSD + Flashcache + udev + Partition uuid > > Hi, > > On 03/19/2015 10:41 PM, Nick Fisk wrote: > > I'm looking at trialling OSD's with a small flashcache device over > > them to hopefully reduce the impact of metadata updates when doing > small block io. > > Inspiration from here:- > > > > http://comments.gmane.org/gmane.comp.file-systems.ceph.devel/12083 > > > > One thing I suspect will happen, is that when the OSD node starts up > > udev could possibly mount the base OSD partition instead of > > flashcached device, as the base disk will have the ceph partition uuid > > type. This could result in quite nasty corruption. > I ran into this problem with an enhanceio based cache for one of our > database servers. > > I think you can prevent this problem by using bcache, which is also integrated > into the official kernel tree. It does not act as a drop in replacement, but > creates a new device that is only available if the cache is initialized correctly. A > GPT partion table on the bcache device should be enough to allow the > standard udev rules to kick in. > > I haven't used bcache in this scenario yet, and I cannot comment on its speed > and reliability compared to other solutions. But from the operational point of > view it is "safer" than enhanceio/flashcache. I did look at bcache, but there are a lot of worrying messages on the mailing list about hangs and panics that has discouraged me slightly from it. I do think it is probably the best solution, but I'm not convinced about the stability. > > Best regards, > Burkhard > _______________________________________________ > 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
 |