[sheepdog-users] cache flush: all or nothing

[MORITA Kazutaka]

At Thu, 06 Jun 2013 23:04:01 +0800,
Liu Yuan wrote:
> 
> > 
> > Remember that I saw almost no network activity on the node after I've
> > been writing data to the guest (max 100kbit/s).
> 
> So FLUSH wasn't issued from VM

I suspect that Valerio uses ext3 and an older kernel (earlier than
Linux 3.1).  Then file system barriers are not enabled by default and
fsync() inside the guest OS doesn't issue flushes at all.  Or,
Perhaps, Valerio might set 'barrier=0' manually to the mount option.

We must not assume that the guest OSes issues flush requests
periodically.  It completely depends on how the users configure their
file systems.

Thanks,

Kazutaka