[zfs-discuss] best practice to pass zfs volume to qemu/kvm

Gordan Bobic gordan.bobic at gmail.com
Tue Feb 16 06:34:47 EST 2016


On Tue, Feb 16, 2016 at 11:24 AM, thibaut noah <thibaut.noah at gmail.com>
wrote:

> Compression on the zfs pool is not possible since i use most of my cores
> for my gaming vm, read and write datas with compression on will drain too
> much power from my cpu.
>


LZO and LZ4 compression is cheap enough that you almost certainly won't
notice it. And even with CPU shortage, it is unlikely to particularly
affect your gaming experience since games don't do a lot of disk I/O except
when loading levels (which isn't particularly CPU intensive game-wise). In
other words, the CPU that disk compression will cost you will be at times
when nothing else is using it anyway. Also note that decompression part is
nearly free in terms of CPU usage, so it's only on disk writes that there
will be an observable CPU usage penalty from compression.



>
> "Some hypervisors also have the ability to share a folder with a guest -
> as shared folder thing - with a toolset in the vm. "
> Seems that it is indeed possible, what is the different between concurrent
> access through the vm and concurrent access through cifs sharing?
>


I'm not entirely sure but I suspect the former actually does something very
similar to the latter. IIRC it was only VirtualBox that provides this
feature, and I tend to avoid VirtualBox at all costs (it's performance and
stability issues make it completely unworkable for any serious application
in my fairly extensive experience).



>
> From what i read it will be a pain, seems that i will have to configure
> things on the guest too apparently.
> Hopefully the bridge i setup will not be a problem with cifs.
>
> Also, it seems that one can remove a disk from a mirror and add another
> (or the same) disk to reconstitute a mirror, if so isn't that possible to
> get one disk out, create a zvol on it, backup datas on that zvol and then
> mirrored the zvol with the disk left on the original pool?
>


That last sentence doesn't quite parse. What exactly are you trying to
achieve?
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