On Fri, 23 Dec 2011, Wido den Hollander wrote: > Hi, > > On 12/23/2011 08:21 AM, Eric_YH_Chen@xxxxxxxxxxx wrote: > > Hi, all: > > > > I am curious about why ceph cluster only support odd number monitors. > > It doesn't only support a odd number. A even number of monitors works in > theory, but it's recommended to use a odd number to get a majority. Right. A bit more detail: Running an even number of monitors means a slightly higher risk of failure than running one less monitor. For example, if you run 3 monitors, you can tolerate 1 failure (2 is a strict majority). And you have 3 machines that can fail. On the other hand, if you run four, you can still only tolerate 1 failure (3 is a majority but 2 is not). But then you have 4 machines that can potentially fail, and your risk of 2 dying is slightly higher. The difference is risk is probably pretty small for most failure rates, but, generally speaking, odd numbers are slightly better. sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
