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. > 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). Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v _______________________________________________ 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/NYD2UNKQPIOK663RXSQCPVCWMSBFPXGI/
