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. >> 2. There would be no data loss in case of host or hypervisor crash. >> Worst case, if guest operating system was corrupted sysadmins would need >> to trigger VM install. > > Host crash => yes you'd definitely need to reinstall that VM. > > It's not a worst case, a host crash would near-definitely corrupt a VM > that was ignoring flush requests. It might even corrupt in an > undetectable way (eg. throwing away data while leaving metadata > intact). > I patched kojivm code once, at the time I think new VM instances all used qcow2 overlays ontop of a shared base. It's possible those are created and destroyed with each VM instance, so data loss may not matter in the case of a crash if the overlay will just be discarded regardless. Would need koji devs to confirm though - Cole _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org Fedora Code of Conduct: https://getfedora.org/code-of-conduct.html List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/G3N2NB6XS5XYU2SU2DLPOWR7YXFRX6FW/
