[Libguestfs] [PATCH virt-v2v v2] v2v: -o libvirt: Remove cache=none.

[Pino Toscano]

On Tuesday, 19 May 2020 17:51:40 CEST Richard W.M. Jones wrote:
> Traditionally if you did live migration (KVM to KVM), you had to
> ensure that cache=none was set on all disks of the guest up front.
> This was because of quirks in how NFS works (I think the close-to-open
> consistency and the fact that during live migration both qemus have
> the file open), and we had to assume the worst case that a guest might
> be backed by NFS.
> 
> Because of this when virt-v2v converts a guest to run on KVM using
> libvirt it sets cache=none.
> 
> This is not necessary with modern qemu.  If qemu supports the
> drop-cache property of the file block driver, which libvirt will
> automatically detect for us, then libvirt live migration is able to
> tell qemu to drop cached data at the right time even if the backing is
> NFS.
> 
> It also had a significant performance impact.  In some synthetic
> benchmarks it could show 2 or 3 times slower performance.
> 
> Thanks: Ming Xie, Peter Krempa.
> ---

There is one additional occurrence of it in virt-v2v-output-local.pod.
With that fixed, LGTM.

Thanks,
-- 
Pino Toscano
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