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Re: [vfio-users] setting up virtual disks



On Tue, 2017-03-28 at 16:01 +0200, Laszlo Ersek wrote:
> On 03/28/17 15:41, Patrick O'Callaghan wrote:
> > On Tue, 2017-03-28 at 15:08 +0200, Laszlo Ersek wrote:
> > > On 03/28/17 14:21, Patrick O'Callaghan wrote:
> > > > On Tue, 2017-03-28 at 11:47 +0200, Laszlo Ersek wrote:
> > > > > I recommend the following setup:
> > > > > 
> > > > > - hard disk(s):          virtio-blk or virtio-scsi disk, as you prefer
> > > > 
> > > > I'm interested in why someone would prefer one over the other. Can you
> > > > explain?
> > > 
> > > I prefer virtio-scsi because it supports thin provisioning (UNMAP scsi
> > > operation); it lets me conserve space in host filesystems that support
> > > discard (such as ext4 or xfs, for example -- there may be more). Given
> > > the right configuration, if you delete files in your Windows 8 or
> > > Windows 10 VM, the space is eventually released on the host filesystem.
> > 
> > OK, thanks.
> > 
> > > With virtio-blk, the software stack is less featureful and thereby
> > > thinner, which is said by some to lead to better performance. Also, as
> > > far as I know, dataplane is only available for virtio-blk at the moment,
> > > it is in progress for virtio-scsi. (I could be out of date on that
> > > though.) YMMV.
> > 
> > No idea what that is. As I'm not provisioning multiple high-load
> > servers, does this matter to me?
> 
> I couldn't give you more authoritative documentation than what google
> turns up, so please go ahead and search for it yourself. Personally, I
> have never ever set up virtio-blk dataplane, in my short or long term
> guests (some of which use GPU or other device assignment as well), and I
> have no complaints about IO performance. (I too don't run production
> servers, like you.) The bottleneck on my laptop has always been SSD
> capacity (even with two SSDs), which virtio-scsi (with unmap/discard
> enabled) has remedied impeccably. I guess, if you haven't complained to
> yourself about IO performance, don't bother with dataplane.

That's fine, thanks.

poc


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