On Sun, Jan 27, 2008 at 02:53:46PM +0000, Gareth Bult wrote: > Ok, question; > > Does TAP:AIO work on networked filesystems .. my testing says not. It does on Fedora / RHEL at least - it should work on any FS that supports direct IO & async IO. > XEN without a good underlying cluster filesystem is to say the > least "limited". If you can't use AIO in this sort of environment, > it also becomes limited .. and if libvirt requires this, it means > libvirt can't be used on large-scale roll-outs on (certain?) > network filesystems. We need to fix libvirt so that stats work with file: based devices too. We just need to figure out the logic required in order to generate the correct device ID. > Interestingly (looking at the Xen list re; performance problems) > I'm getting > 65Mb/sec on my DomU's .vs. 70Mb/sec on my host > nodes Dom0 ... and it's proving to be reliable atm .. You ought to be able to get within 5% of host performance when using either phy: (for real block devs) or tap:aio:. NB make sure you do *not* use sparse files - fully allocate the file if you want good performance. Sparse file have terrible performance characteristics as blocks as allocated on-demand which causes metadata syncs of the underlying host FS, which serializes all I/O operations. > Be interesting to know why Xen only documents "file" given > the critical nature / apparent flaws in the driver. Xen documentation leeaves alot to be desired :-( > Is there "no" way of forcing a loopback interface to flush itself? Unfortunately not - its inherant in the impl of loop devices. Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=| -- Libvir-list mailing list Libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list