On 21/08/2019 18:05, DHilsbos@xxxxxxxxxxxxxx wrote: > Florian; > > Forgive my lack of knowledge of OpenStack, and your environment / use case. > > Why would you need / want to snapshot an ephemeral disk? Isn't the point of ephemeral storage to not be persistent? Fair point, but please consider that if you use an ephemeral VM as a template for other VMs (a common motivation for snapshotting), you might not care about the consistency of the VMs themselves, but you probably do care about the consistency of the template. But, for that use-case you could argue that you should just shut down the VM and take a clean snapshot then. However, in OpenStack Nova you may also use boot-from-volume, meaning you're running a VM that is expected to be *wholly* persistent, rather than ephemeral, and in that case the consistency of a snapshot taken while the instance is running is rather important. So just to be sure I took your cue and retested to see whether the same issue also applied to an instance using boot-from-volume. And lo and behold, the problem does not apply — if I configure an instance to boot from a volume, I get fsfreeze just as intended. (I have yet to dig up the code path for this.) So, evidently the situation can be summarized as: - Ephemeral boot, *without* RBD, with or without attached volumes: freeze/thaw if hw_qemu_guest_agent=yes, resulting in consistent snapshots. - Ephemeral boot *from* RBD, also with or without attached volumes: no freeze/thaw, resulting in potentially inconsistent snapshots even with hw_qemu_guest_agent=yes. - Boot-from-volume from RBD: freeze/thaw if hw_qemu_guest_agent=yes, resulting in consistent snapshots. Bit odd, that. :) But at least there's another available workaround: if you need to ensure snapshot consistency, use boot-from-volume. Thanks for the nudge in that direction, Dominic! Cheers, Florian _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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