Re: [Qemu-devel] virtio ssd caching

[Stefan Hajnoczi]

On Tue, Sep 06, 2016 at 12:44:39PM +0430, Aarian P. Aleahmad wrote:
> I am looking for a solution to cache a VM on a SSD without the guest
> knowing about it. We can do it by caching the disk on which the VM's disk
> is lcoated with a SSD or we can do it through the hypervisor (i.e. Qemu,
> KVM, etc.).
> 
> I was thinking about passing an ssd device to the hypervisor as a cache
> disk (e.g. passing /dev/sdb to the hypervisor) or making a new virtual disk
> image and storing it on a SSD and passing the SSD located vDisk to the
> hypervisor as a cache.
> 
> Thus, I would like to know whether is it possible or not, and if not, if I
> wish to implement such a thing, what should I do and whether is there any
> reusable code to do so or not?

QEMU itself doesn't offset tiering/caching but you can use the host
kernel's bcache or dm-cache features to achieve this.

I haven't tried them myself so I can't give exact command-lines.
Richard Jones posted a tutorial in 2014:
https://rwmj.wordpress.com/2014/05/22/using-lvms-new-cache-feature/

Stefan

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