[Ceph-users] Re: Ceph MON onde RAM recommandations

RAM recommendations are tricky. We feel compelled to come up with a formula, but there are multiple factors. I will share my experience : We started with min 32 GB per mon, which seemed fine for 12x24 OSDs. As one specific cluster grew to 41x24 I found that 32 was enough for steady-state runtime, but not enough to boot. I did emergency upgrades to avert disaster. I’ve seen occasions where one mon in any cluster going down caused another, perhaps the new leader but not necessarily, to spike to >100 GB used. Sometimes a heap release works, sometimes restarts are needed. The number of PGs is likely a factor as is the OS - this is on Ubuntu Trusty. Some time ago there was discussion where Sage expressed a belief that newer releases of TCmalloc behave better. Also remember the Ceph-mgr daemon running in parallel. Usage can grow during distress events too. In my situation 128 GB is the min I’ll accept. YMMV.