What I suspected and tested without success yesterday seem to be, finally, a solution.
The issue, in my situation, may be caused by the fact that the exported entity in /etc/exports did not match the mounted path as a VMware datastore : I exported the volume, and mounted the qtree.
After changing /etc/exports to set the export path to the qtree, it seem to be ok.
The thing is :
- I had to wait a little while after exporting the fs again (exportfs -a) : no need to rediscover Host Service, but had to wait like 10 mn for the link to establish
- It is possible I had to put a VM in the datastore for the storage controller association to work, but I'm not sure about that.