On Apr 1, 2013, at 3:33 PM, Gregory Farnum <g...@inktank.com> wrote:

>> On Mon, Apr 1, 2013 at 2:16 PM, Sam Lang <sl...@inktank.com> wrote:
>>> On Mon, Apr 1, 2013 at 5:59 AM, Papaspyrou, Alexander
>>> <papaspy...@adesso-mobile.de> wrote:
>>> 1. So far, I understand that OSD ids have to be numeric, nothing else in
>>> there. What I couldn't find is whether they really have to start at 0 or 1,
>>> and whether I need to increase them stepwise? The background of my question
>>> is automation: It would make our life much simpler if I could use some
>>> calculated value for the OSD id (say, the node's decimal IP address and some
>>> local ID for the disk), because we could then statically assign them without
>>> having to know what other OSDs already exist.
>> 
>> They need to start from 0.  The max_osd value maintained by the
>> monitor bounds the number of possible osds, keeps the size of the
>> osdmap down, etc.
> 
> Note that using the "ceph osd create" command gives you an ID to use
> these days, and that's where you should be deriving these from.
> There's no support at all for making up your own OSD IDs; sorry.

NOW you tell me.. :) I have a small cluster where I am using the first digit of 
the OSD to indicate which server it is in and the second to indicate which disk 
in that server it uses. Aside from occasional spurious entries (for the missing 
digits) in the CRUSH map it seems to work fine.

Can you elaborate on why this might be Bad? I'm planning and beginning to 
deploy a larger cluster and was going to use four-digit OSD id's (two for the 
server, two for the disk). What problems should I expect if I do that?

How hard would it be to support making up one's own OSD ID's?

I would also suggest that this be better documented on the website. The 
5-minute quickstart says nothing about ID constraints and offers only 0 and 1 
as examples. The "ceph-conf" page says only that "the instance ID for an OSD is 
always numeric". The "add-or-rm-osds" page mentions "ceph osd create" and its 
ability to set a "UUID" automatically, but only after several steps that 
require you to already know the "osd-number".

Thanks,

JN

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