On Feb 25, 2014, at 2:16 AM, Justin Ossevoort <jus...@internetionals.nl> wrote:

> I think in principle: No.
> 
> It is something that should be documented as advise in the VM software 
> documentation. But things like storage management is the domain of the 
> distribution or systems administrator.

No, that's a recipe for users having a chaotic experience. Either the VM 
managing application needs to set +C on image files, or the file system needs 
to be optimized for this use case. Consider the Gnome Boxes user. They're not 
in a good position to do this themselves, and each distro doing this causes 
fragmented experience. It's better if the application developer (Gnome Boxes, 
VMM) or possibly libvirt to set +C on VM images; or as a general purpose file 
system for it to be optimized for this use case.

Either way it leaves the end user out of what amounts to esoteric configuration.


> There might be a situation where the VM software can directly use a btrfs 
> filesystem for it's storage engines where it could be sensible to add such a 
> thing, but in that case it's already directly managing it's subvolumes and 
> can turn nodatacow on/off when appropriate.

I don't expect VM's to use subvolumes directly, instead of image files (qcow2, 
raw, vmdk, etc) for a while, and also I'm not sure if there's enough separation 
between VMs, or VM and host sharing what is really one file system. If there's 
any possibility a misbehaving VM could corrupt the file system and not merely 
its own tree, then it's unlikely a best practice.



Chris Murphy

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