Hi min, just like Paul already explained. The cache is made out of OSD's ( which have just like any other OSD's their own journal ). So it depends on you what structure you will build. You can place all journals of hot and cold storage ( hot = cache, cold = regular storage ) together on same SSD's. You can also place the journal on the OSD's for the cache itself. You can also have special SSD's who hold all journals for the cache OSD's. And so on. ----- http://docs.ceph.com/docs/master/rados/operations/cache-tiering/ points on http://docs.ceph.com/docs/master/rados/operations/crush-map/#placing-different-pools-on-different-osds So to build up cache, you will have first to create all OSD's you need ( hot and cold ones ). Then you will devide this OSD's into two pools with the crush map. Then you will make one of the pools the cache. -- Mit freundlichen Gruessen / Best regards Oliver Dzombic IP-Interactive mailto:info@xxxxxxxxxxxxxxxxx Anschrift: IP Interactive UG ( haftungsbeschraenkt ) Zum Sonnenberg 1-3 63571 Gelnhausen HRB 93402 beim Amtsgericht Hanau Geschäftsführung: Oliver Dzombic Steuer Nr.: 35 236 3622 1 UST ID: DE274086107 Am 21.04.2016 um 13:42 schrieb min fang: > thanks Oliver, does the journal need be committed twice? One is for > write IO to the cache tier? the other is for write IO destaged to SATA > backend pool? > > 2016-04-21 19:38 GMT+08:00 Oliver Dzombic <info@xxxxxxxxxxxxxxxxx > <mailto:info@xxxxxxxxxxxxxxxxx>>: > > Hi, > > afaik cache does not have to do anything with journals. > > So your OSD's need journals, and for performance, you will take SSD's. > > The Cache should be something faster than your OSD's. Usually SSD or > NVMe. > > The Cache is an extra Space in front of your OSD's which is supposed to > speed up things because the cache operate faster than the OSD's and the > cache will flush its content to the slower OSD's. > > So, the cache is independent from the OSD's. And this way, from their > journals. > > And, the cache >must< be on faster drives than the OSD's, otherwise you > wont see any performance increase. > > -- > Mit freundlichen Gruessen / Best regards > > Oliver Dzombic > IP-Interactive > > mailto:info@xxxxxxxxxxxxxxxxx <mailto:info@xxxxxxxxxxxxxxxxx> > > Anschrift: > > IP Interactive UG ( haftungsbeschraenkt ) > Zum Sonnenberg 1-3 > 63571 Gelnhausen > > HRB 93402 beim Amtsgericht Hanau > Geschäftsführung: Oliver Dzombic > > Steuer Nr.: 35 236 3622 1 <tel:35%20236%203622%201> > UST ID: DE274086107 > > > Am 21.04.2016 um 13:27 schrieb min fang: > > Hi, my ceph cluster has two pools, ssd cache tier pool and SATA > backend > > pool. For this configuration, do I need use SSD as journal device? > I do > > not know whether cache tier take the journal role? thanks > > > > > > _______________________________________________ > > ceph-users mailing list > > ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx <mailto: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
 |