[HTCondor-users] Drained 0 machines

[Stefano Dal Pra <stefano.dalpra@xxxxxxxxxxxx>]

Hello,
trying to configure Defrag on condor 8.8.9.
I need some help to understand this message in the DefragLog:

07/17/20 20:08:13 Looking for 15 machines to drain.
07/17/20 20:08:17 Drained 0 machines (wanted to drain 15 machines).

What is the condition used by Defrag to consider a machine available for 
draining?

Thanks for any hint,
Stefano