On Mon, 2018-07-16 at 09:27 -0400, Cole Robinson wrote:
On 07/15/2018 11:47 AM, Richard W.M. Jones wrote:
> On Fri, Jul 13, 2018 at 04:05:42PM +0200, Mikolaj Izdebski wrote:
> > On 07/12/2018 10:17 PM, Richard W.M. Jones wrote:
> > > Does each build start with its own fresh VM? Do you care about the
> > > data in that build VM if either qemu or the host crashes? If the
> > > answers are 'Yes' and 'No' respectively to these questions
then IMHO
> > > this is the ideal situation for cache=unsafe.
> >
> > The answers are 'No' and 'Not much'.
> >
> > 1. VMs are installed once and are running for week/months until they are
> > reinstalled. In the meantime guests and hosts are rebooted during
> > routine maintenance, to apply updates.
>
> In this case my preferred advice would be: DO NOT use cache=unsafe.
>
> We've only tested scenarios for very short-lived build or temporary
> VMs (for example when I was building RISC-V packages before we had
> Koji, I used a script which created a VM per build and there it made
> sense to use cache=unsafe).
>
> I do not think it's a good idea to be using this for VMs which are in
> any way long-lived as there could be unforeseen side effects which I'm
> not aware of and certainly have never tested.
>
One other datapoint is that I _think_ openqa uses cache=unsafe, which is
used for Fedora automated install testing. I'm basing this largely on
cache=unsafe in the openqa sources.
That's mostly true, I think, except when doing multipath testing (where
it uses cache=none instead). However, openQA very much meets the
definition of 'short-lived / temporary' VMs - each openQA 'job' uses a
new VM, so the longest any one ever lasts is 2 hours (the hard limit on
an openQA job's lifetime). It also uses fresh disk images each time
(even when using a pre-created base disk image, it doesn't use it
directly but creates new scratch images based on the base image). I
don't know whether this is true of the Koji builder VMs.
--
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Twitter: AdamW_Fedora | XMPP: adamw AT happyassassin . net
http://www.happyassassin.net