managed to fix it myself :)
Did a
cat
/rhev/data-center/mnt/glusterSD/10.70.7.17\:_vmstore13/9f731135-f5d9-4609-9e3b-fa9cae75e314/images/5aa438e3-8d22-4b6c-bccf-a843151ca0be/0795e58c-4960-413a-a0b4-e8a6d547fda5.meta
on the host the gluster file system was mounted from (vmhost17, IP 10.70.7.17), got
"file not found", repeated the same command, this time successful and the
problem went away.
Probably some strage glusterfs problem and not directly related to oVirt.
Just in case someone stumbles accross the same thing ...