On 04/05/2013 05:02 PM, Dimitri Maziuk wrote:
On 4/5/2013 7:57 AM, Wido den Hollander wrote:
You always need a majority of your monitors to be up. In this case you
loose 66% of your monitors, so mon.b can't get a majority.
With 3 monitors you need at least 2 to be up to have your cluster
working.
That's kinda useless, isn't it? I'd've thought "2 copies on-site and one
off-site, and if the main site room's down we can work off the off-site
server" is a basic enough HA setup -- we've had it here for some time.
Now you tell me ceph won't even do that?
It's a design principle that you need a majority.
Think about it this way. You have two racks and the network connection
between them fails. If both racks keep operating because they can still
reach that single monitor in their rack you will end up with data
inconsistency.
The majority of monitors is there to prevent you from having "rogue"
parts which still operate without network connections with the rest.
So it's not useless, it's a way to keep everything consistent.
You should place mon.c outside rack A or B to keep you up and running in
this situation.
Dima
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Wido den Hollander
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