I used to have that before too, it was whenever something was re-indexed...
It seems like ever since 9.5.1 this has been fixed for me, it seems to automatically detect that it was re-indexed
Could be a couple things. First it means the volume is in an unknown state. This could be caused by a flaky snmp agent, re-indexing of the volumes, re-imaging of the particular systems. You can use the Solarwinds Toolset SNMP MIB browser to check the iftable MIB on the device. Then look at the IFOper status and the IF Admin status to determine if these values are coming back with out an up or down then Orion will mark these unknown.
Try to unmanage and manage the device to reset this.
I also get the blue question mark (unknown) resources as a relatively common occurance. In the case that SNMP is working is this just a re-index that has taken place?
Also, will these eventually be removed automatically or do I have to manually go through and clean these up?
Somebody... anybody...???
This unknown resource thing is confusing as I don't know the cause for sure and don't know what to do with them.