A word of caution: While normally my OSDs use very little CPU, I have occasionally had an issue where the OSDs saturate the CPU (not necessarily during a rebuild). This might be a kernel thing, or a driver thing specific to our hosts, but were this to happen to you, it now impacts your VMs as well potentially. And even during a rebuild, but when things are acting normally, CPU usage goes up by a lot relative to steady-state for periods. On top of this, you would also be sharing other system resources which would be potential abuse vectors -- network for one. I would avoid.
On Thu, Mar 26, 2015 at 8:11 AM, Wido den Hollander <w...@42on.com> wrote: > On 26-03-15 12:04, Stefan Priebe - Profihost AG wrote: > > Hi Wido, > > Am 26.03.2015 um 11:59 schrieb Wido den Hollander: > >> On 26-03-15 11:52, Stefan Priebe - Profihost AG wrote: > >>> Hi, > >>> > >>> in the past i rwad pretty often that it's not a good idea to run ceph > >>> and qemu / the hypervisors on the same nodes. > >>> > >>> But why is this a bad idea? You save space and can better use the > >>> ressources you have in the nodes anyway. > >>> > >> > >> Memory pressure during recovery *might* become a problem. If you make > >> sure that you don't allocate more then let's say 50% for the guests it > >> could work. > > > > mhm sure? I've never seen problems like that. Currently i ran each ceph > > node with 64GB of memory and each hypervisor node with around 512GB to > > 1TB RAM while having 48 cores. > > > > Yes, it can happen. You have machines with enough memory, but if you > overprovision the machines it can happen. > > >> Using cgroups you could also prevent that the OSDs eat up all memory or > CPU. > > Never seen an OSD doing so crazy things. > > > > Again, it really depends on the available memory and CPU. If you buy big > machines for this purpose it probably won't be a problem. > > > Stefan > > > >> So technically it could work, but memorey and CPU pressure is something > >> which might give you problems. > >> > >>> Stefan > >>> > >>> _______________________________________________ > >>> ceph-users mailing list > >>> ceph-users@lists.ceph.com > >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > >>> > >> > >> > > > -- > Wido den Hollander > 42on B.V. > > Phone: +31 (0)20 700 9902 > Skype: contact42on > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > -- David Burley NOC Manager, Sr. Systems Programmer/Analyst Slashdot Media e: da...@slashdotmedia.com
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