[ceph-users] Hangs with qemu/libvirt/rbd when one host disappears

Marcus Priesch marcus at priesch.co.at
Thu Dec 7 03:48:51 PST 2017


Hello Fabian,

> an even number is always bad for quorum based systems (6 is no better
> than 5, as you can only tolerate a loss of 2 before losing quorum).
> 
> in Ceph, additional monitors require additional resources AND generate
> additional overhead (more mons -> more communication). the rule of thumb
> is 3 for small to mid-sized cluster. the next step up performance wise
> would be to move the 3 mons to their own stand-alone nodes, and only
> once that starts to bottleneck, you increase the number to 5 and/or
> upgrade the HW to become faster. for really big clusters, you can then
> start splitting out the mgr instances to reduce the load further.

ok, so i will turn back to only having three mon's.

does this also hold for mgr's ?

and: most important, can this lead to my problems ? just by having too
much mon's ?

thanks,
marcus.


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