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I think the idea is that a VM's OS might just blindly go on writing, or even stop the write and not write some important piece of data.  The idea behind pausing the VM would be that someone could hypothetically fix the error (allocate more space for the disk, etc) and resume the VM, thus not losing the data that was to be written.

----- Original Message -----
From: "Robert Collins" <robertc at robertcollins.net>
To: "OpenStack Development Mailing List" <openstack-dev at lists.openstack.org>
Sent: Monday, June 10, 2013 2:17:05 PM
Subject: Re: [openstack-dev] Discussion of Nova Bug 1189543 (Setting drive error policy in Nova)

On 11 June 2013 04:45, Solly Ross <sross at redhat.com> wrote:
> (https://bugs.launchpad.net/nova/+bug/1189543)
>
> It was proposed at RedHat (https://bugzilla.redhat.com/show_bug.cgi?id=865336) that we should explicitly set Libvirt to stop VMs on drive read/write errors, and then detect that and somehow set a piece of state in nova.

It's not obvious to me why you'd stop the VM : that will cause
auto-scaling systems to detect it as down, detach the volume and spin
it up elsewhere, but if the fault is in the volume, the new instance
will just pause and on it goes.

I/O errors are a known part of the machine model: what is the data
loss that that bug talks about if the VM isn't paused?

-Rob

-- 
Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Cloud Services

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