Single DS drivers: discussion

[1gramos]

"Single DS drivers" are those whose underlying storage is the same for images and disks. Currently we have two: Ceph and "pure" LVM.

I noticed two inconsistencies in Ceph during development of issue #7185, and there are probably some more, so this issue is an "umbrella" for stuff related to these type of drivers:

• The monitor script is called twice and at the same time, one for the SYS datastore and other for the IMG datastore. Which happen to be the same in this case, even the monitoring operations are symlinked. But removing any of them shows errors in the oned.log file. I think we should disable monitoring SYS datastores in single DS drivers, and move the MONITOR_VM_DISKS code (ImageManager.cc) to IMG datastores for these cases.
• (Probably Ceph specific) BRIDGE_LIST is a mandatory attribute in Ceph datastores, but oned only prevents removal from the IMG ds. Removing it from the SYS ds is allowed. Which 1) is confusing, and 2) breaks monitoring currently (unless fixing the previous point). Also, docs say that all attributes must be defined in both datastores which is probably not true for most of them, and again can be problematic if the user updates something only in one of them. We should split that list by attributes required in "SYS/DS/BOTH".