Re: [PATCH 4 of 4 V5] tools/xl: Remus - Network buffering cmdline switch

[Brendan Cully <brendan@cs.ubc.ca>]

On Thursday, 12 December 2013 at 10:52, Shriram Rajagopalan wrote:
> >
> >
> > > >
> > > > Is Remus actually useable without network buffering ?  I don't think
> > > > we would want to change the default later, and clearly the default
> > > > should be to behave correctly.
> > > >
> > >
> > > It is usable without network buffering. Memory state is preserved on
> > > failover.
> > > On failover, without network buffering, exising network
> > > connectivity (tcp connections) "may" be lost, under some circumstances.
> >
> > uh, wouldn't it be possible to acknowledge client requests whose
> > backing state hasn't been replicated? So that on failover the backup
> > might have no memory of a promised it had made? it's more than just
> > tcp resets, isn't it?
> >
> >
> true.. which is why I stated ..
> 
>  > You are right about the fact that for Remus to behave 'correctly', one
> > > needs both network and disk buffering -- the latter being absent is the
> > > reason
> > > Remus in libxl is still experimental.

ah, maybe you meant to leave the quotes off of 'correctly'.

> > >
> > > So, might as well enable network buffering by default, punt if the
> > support
> > > is
> > > missing and suggest that the user invoke Remus without network buffering
> > > (while providing sufficient warnings that the failover may be incomplete)
> > >
> >
> 
> :)