[sheepdog] [PATCH] tests: add a test to test vdi snapshot functionality concurrently

[Liu Yuan]

On 09/19/2012 07:29 PM, MORITA Kazutaka wrote:
> I'm still testing and trying to understand what is the problem, but
> looks working almost correctly, at least for now.  The only problem I
> encountered is that sheep pulled deleted vdi objects to the local
> cache directory and this is the reason why the master branch doesn't
> pass tests/044.  However, it is not a fatal problem, I think, because
> sheep just only caches the info that the object is deleted.
> 
> When object cache is enabled, collie accesses object with a
> writethrough mode - is it a really problem?  What is the scenario
> where data inconsistency actually happens?

Yes, I do meet the inconsistency problem. For e.g, on node A you issue collie
command to pull the VDI object to the local node. Then there is a gateway request
that is to modify the VDI from node B. This request won't access the cached object VDI
at all on node A. After this request, cached object VDI is older than the copies in
the backend and we'll read the older VDI on node A.

Thanks,
Yuan