vSphere Storage IO Control (SIOC) and "external i/o workload is detected on datastore" messages

[pirx4711]

I've enabled SIOC on all our Lefthand vSphere 4.1 datastores. No other devices are accessing the SAN (12 LH nodes, 6 ESXi hosts). Since I enabled SIOC I see the warning "external i/o workload is detected on datastore" every 2-3 minutes for each datastore.

There are some articles that describe the problem.

http://kb.vmware.com/kb/1020651

http://www.yellow-bricks.com/2011/01/20/enable-storage-io-control-on-all-datastores/

SIOC is enabled on all datastores, the threshold is 30ms everywhere.

I've no idea what might cause this issue? Any ideas?