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

[Anthony Liguori <anthony@codemonkey.ws>]

Daniel P. Berrange wrote:
> On Wed, Feb 25, 2009 at 07:04:22PM +0200, Gleb Natapov wrote:
>   
>> 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.

This simply doesn't happen in practice.  The FS needs to write data to 
the disk in order to remount it read-only.  Once all writes start 
failing, the errors are cascading.

>  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
>   
My contention is that a user using a management app is already hosed 
with "report".  To not be fubar, we need async notifications.  If we can 
the default to enospc, I think it makes nothing worse but a good chunk 
of cases a lot better.

Regards,

Anthony Liguori


> Daniel
>