> On Nov 1, 2017, at 4:45 PM, David Turner <drakonst...@gmail.com> wrote:
> 
> All it takes for data loss is that an osd on server 1 is marked down and a 
> write happens to an osd on server 2.  Now the osd on server 2 goes down 
> before the osd on server 1 has finished backfilling and the first osd 
> receives a request to modify data in the object that it doesn't know the 
> current state of.  Tada, you have data loss.

I’m probably misunderstanding, but if a osd on server 1 is backfilling, and its 
only candidate to backfill from is an osd on server 2, and the latter goes 
down; then wouldn’t the osd on server 1 block, i.e., not accept requests to 
modify, until server 1 comes up again?
Or is there a ‘hole' here somewhere where server 1 *thinks* it’s done 
backfilling whereas the osdmap it used to backfill with was out of date?

Thanks, 

Hans
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