The virtualized MON will be on a completely different platform and won't use any of the ceph cluster resources (either compute or disk). I was thinking of putting the 'master' MON (the one with the lowest IP) on a dedicated server because I read the load is heavier on this one (lots of logs in particular).
Adrien On Sun, Jul 5, 2015 at 6:17 PM, Paul Evans <[email protected]> wrote: > On Jul 4, 2015, at 2:44 PM, Adrien Gillard <[email protected]> > wrote: > >> >> Lastly, regarding Cluster Throughput: EC seems to require a bit more CPU >> and memory than straight replication, which begs the question of how much >> RAM and CPU are you putting into the chassis? With proper amounts, you >> should be able to hit your throughput targets,. >> >> Yes, I have read about that, I was thinking 64 GB of RAM (maybe >> overkill, even with the 1GB of RAM per TB ? but I would rather have an >> optimal RAM configuration in terms of DIMM / channels / CPU) and 2x8 Intel >> cores per host (around 2Ghz per core). As the cluster will be used for >> backups, the goal is not to be limited by the storage backend during the >> backup window overnight. I do not expect much load during daytime. >> >> >> 64G is “OK” provided you tune the system well and DON”T add extra >> services onto your OSD nodes. If you’ll also have 3 of them acting as >> MONs, more memory is advised (probably 96-128G). >> > > At the moment I am planning to have a smaller dedicated node for the > master monitor ( ~ 8 cores, 32G RAM, SSD) and virtual machines for MON 2 > and 3 (with enough resources and virtual disk on SSD) > >> > > It would be good to have others comment on the practicality of this > design, as I don’t believe there is a benefit to having a single MON that > is ‘better' than the other two. My reasoning comes from a limited > understanding of the Paxos implementation within Ceph, which suggests that > a majority of MONs must be available at all times (i.e. - 2 of the 3), and > that MON activities will be processed according to the speed of the slowest > quorum member. If two of the MONs are running as VMs on OSD hosts, and you > have a write-heavy workload, I can foresee some interesting resource > contention issues that might sometimes destabilize your entire cluster. > YMMV. > - Paul >
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