Re: OSD replacement feature

[David Zafman <dzafman@redhat.com>]

There are two reasons for having a ceph-disk replace feature.

1. To simplify the steps required to replace a disk
2. To allow a disk to be replaced proactively without causing any data 
movement.

So keeping the osd id the same is required and is what motivated the 
feature for me.

David

On 11/20/15 3:38 AM, Sage Weil wrote:
> On Fri, 20 Nov 2015, Wei-Chung Cheng wrote:
>> Hi Loic and cephers,
>>
>> Sure, I have time to help (comment) on this feature replace a disk.
>> This is a useful feature to handle disk failure :p
>>
>> An simple step is described on http://tracker.ceph.com/issues/13732 :
>> 1. set noout flag - if the broken osd is primary osd, could we handle well?
>> 2. stop osd daemon and we need to wait the osd actually down. (or
>> maybe use deactivate option with ceph-disk)
>>
>> these two above step seems OK.
>> about handle crush map, should we remove the broken osd out?
>> If we do that, why we set noout flag? It still trigger re-balance
>> after we remove osd from crushmap.
> Right--I think you generally want to do either one or the other:
>
> 1) mark osd out, leave failed disk in place.  or, replace with new disk
> that re-uses the same osd id.
>
> or,
>
> 2) remove osd from crush map.  replace with new disk (which gets new osd
> id).
>
> I think re-using the osd id is awkward currently, so doing 1 and replacing
> the disk ends up moving data twice.
>
> sage
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