On Tue, Feb 26, 2019 at 11:00:41AM +0100, Martin Blapp wrote: > Hi all, > > We have done several speed tests on a qcow2 Linux Image to test how fast > tar-in with a big > tarball can be. Virtio seems to be active, and we get transfers in a range > from 100-160MB/sec, > independent of the disk speed on the host. > > For example we had a 20 core host system with 900MB for serial writing and > 350MB for mixed > read/write on the native filesystem. We've expected a faster tar-in for qcow2 > there than on a > small test system with some slow disks and only two cores. But the rates > where nearly the same. > We tried really hard to do some optimizing and using big files inside the tar > (for emulating serial > writing), but we managed only to get those 160MB/sec, but not more. > > The IO-rate for serial writing inside a running VM-Image on the same qcow2 > image is much more > higher, dependent of course on the underlying disks of the host. Here we get > clear benefits of fast > storage. > > Has anybody of you got more than those 160MB/sec with tar-in, and if so, how > did you do it? > Are there maybe some limitations in the XDR/RPC mechanisms of tar-in ?
I doubt that XDR (note: RPC is not used) is a problem. There is a special streaming mode used for tar-in and similar "upload" commands, and apart from probably an extra copy or two there's very little overhead. Did you try changing the cache mode? https://rwmj.wordpress.com/2013/09/02/new-in-libguestfs-allow-cache-mode-to-be-selected/ You could also try running virt-rescue to get direct access to an appliance and run some tests from within that environment. This gives you an idea of how qemu+virtio is performing directly, without any possible libguestfs overhead. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/ _______________________________________________ Libguestfs mailing list Libguestfs@redhat.com https://www.redhat.com/mailman/listinfo/libguestfs