Discrepancy detection between volumedriver and alba

[kinvaris]

Problem description

Related to openvstorage/volumedriver#176
There is a small possibility that namespaces are leaked due to bugs in the volumedriver

Possible solution

Provide discrepancy check between volumedriver and alba

[wimpers]

How will you know that the vDisk is not in creation? There is a chance that the namespace is created but the volume isn't yet created on the voldrv. Maybe raise if x% are left behind?

[domsj]

How will you know that the vDisk is not in creation?
Keep track of the garbage candidates, and a day or so later check again whether there is a corresponding volume or not... That gives the volumedriver a day time to start using the namespace

I do suggest being careful with something like this. Will you know all vpools (possibly remote ones?) using the backend? What if the backend is used as part of another backend? (You want to make sure you're not throwing away some namespace that may still be used...)