To answer my own post... On Mon, Mar 25, 2019 at 02:45:18PM +0100, Frank Wall wrote:
I've been using oVirt for years and have just discovered a rather strange issue that causes EXTREME high iowait when using a NFSv3 storage.
3145728000 bytes (3.1 GB) copied, 141.649 s, 22.2 MB/s
FWIW, iperf result looks good between the oVirt Node and the NFS storage:
[ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 10.9 GBytes 9.36 Gbits/sec
I did A LOT more tests. Apparently, the iperf test result was not accurate. In fact, iperf returned *very* different results, some as low as 1.1 Gb/s in my 10 Gb/s network. The results were just not stable. Today I've replaced the NIC of my NFS storage server. It was equipped with a Intel X550-T2 NIC. While replacing the NIC I've noticed that it was missing all Intel branding and had no yottamark. The replacement, a Intel X540-T1 looks pretty genuine, has a yottamark and all... A new test with the supposedly genuine Intel NIC showed perfectly stable iperf results, all in the ~9.3 Gb/s range. I'll perform further tests next week, but right now it looks like a fake/counterfeit Intel NIC caused all this trouble. :-/ Regards - Frank