[sheepdog] Is it necessary for outstanding io block leave/join event?

[MORITA Kazutaka]

At Thu, 17 May 2012 14:07:15 +0800,
Liu Yuan wrote:
> 
> >> I think both recovery code and any assumptions need to be revisited and
> >> possibly this is a long term issue.
> > 
> > One question is if we should support the simple store much longer.  Not
> > just in this regard farm has a lot of advantages, while I'm not sure
> > what the added benefit of the simple store is.
> > 
> 
> 
> I'll vote for dropping it. I am not sure if Kazum has any feature to be
> designed on top of simple store.

I thought that one advantage of the simple_store driver was that it
uses a syscall link() to copy objects from local older epochs to the
current epoch, so we could avoid many I/Os in the recovery process.
However, it seems that the link operation of the farm driver is not
called at all on my environment.  Does Farm do the recovery process in
the different way from the simple_store driver?

Thanks,

Kazutaka

> 
> IMHO, dropping the support for simple store will benefit us (by redesign
> higher level code, such as abstracted store layer, recovery to be more
> oriented for Farm):
> 
> 1) better modular store abstraction, which was originally designed for
> simply store layout (objects are tagged by epoch), but comes up with
> many assumptions(restrictions)
> 2) better recovery code logic integrated into Farm, because Farm can be
> easily modified to concurrent object access, partial data migration, etc.
> 
> For compatibility issue, we can provide a script which translate simple
> store layout into Farm.
> 
> Thanks,
> Yuan
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