Re: Crush and Monitor questions

[Bryant Ng <bryantng@gmail.com>]

I guess my question was where is the crushmap (and osdmap) persisted on 
the monitor node?

If the entire cluster goes down, I assume the monitor is reading the 
crushmap from some persistent file stored on disk or a db?  Is that why 
the minimum recommended storage for monitors is 10GB?  Is the crushmap 
and osdmap stored in those 10GB?

-Bryant

Joao Eduardo Luis wrote:
> Hello Bryant,
>
> On 12/11/2012 08:23 PM, Bryant Ng wrote:
>> Hi,
>>
>> I'm pretty new to Ceph and am just learning about it.
>>
>> Where are the CRUSH maps stored in Ceph? In the documentation I see you
>> use the 'crushtool' to compile and decompile the crush map.
>
> The crushmap is kept alongside with the osdmap, and shared by the monitors.
>
>> I understand that if a single monitor comes online, it can talk to the
>> other existing monitors to get the cluster map but how does it work on
>> initial startup?  Or if the entire Ceph clusters goes down b/c of power
>> failure or something.
>
> If you add a new monitor to an existing cluster, it will synchronize
> with the existing monitors and will obtain all their infos, including
> the crushmap. Updates to the crushmap will also be shared among the
> monitors in the quorum.
>
> If you are starting up fresh, you will have to either add your custom
> crushmap to the monitors (using the ceph tool), or stick with the
> default crushmap (which only defines something along the lines of a
> 'default' root, a 'defaultrack' rack and a 'localhost' host).
>
> If the entire cluster goes down... well, if the monitors are not up they
> won't be able to share the crushmap. When they are brought back up, then
> they will pick up where they left. But I'm not sure if I understand what
> your question is.
>
>    -Joao
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