Re: [Qemu-devel] [6388] Stop VM on ENOSPC error.

[Daniel P. Berrange]

On Wed, Feb 25, 2009 at 07:04:22PM +0200, Gleb Natapov wrote:
> On Wed, Feb 25, 2009 at 10:55:25AM -0600, Anthony Liguori wrote:
> > Anthony Liguori wrote:
> >> Revision: 6388
> >>           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=6388
> >> Author:   aliguori
> >> Date:     2009-01-21 18:59:04 +0000 (Wed, 21 Jan 2009)
> >>
> >> Log Message:
> >> -----------
> >> Stop VM on ENOSPC error. (Gleb Natapov)
> >>
> >> This version of the patch adds new option "werror" to -drive flag.
> >> Possible values are:
> >>
> >> report    - report errors to a guest as IO errors
> >> ignore    - continue as if nothing happened
> >> stop      - stop VM on any error and retry last command on resume
> >> enospc    - stop vm on ENOSPC error and retry last command on resume
> >>             all other errors are reported to a guest.
> >>
> >> Default is "report" to maintain current behaviour.
> >>   
> >
> > I recently got burnt by the default being "report".  I was doing an  
> > installation and ran out of disk space.  The guest did not do anything  
> > intelligible with the error reports and froze very hard (as you'd 
> > expect).
> >
> > Any objection to changing to default to enospc?
> >
> Or even to stop. What guest can do with other errors anyway?

The idea is that if the guest at least sees the I/O error, then it won't
continue writing as if everything were OK. It may not be able to continue
normal operation, but it can at least mark the FS read-only and avoid
ongoing damage. So you have a reasonable liklihood of shutting down the
guest, fixing the ENOSPC problem ont he host, and starting the guests
again & them recovering their journal.  'ignore' is guarenteed dataloss,
'report' gives you a good fighting chance. 'stop'/'enospc' are best, if
the management app is able to detect that the VM is being paused & thus
report it to the user

Daniel
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