We had a pair of machines. And some bright spark set them up to mount each others NFS shares. after a power outage "Holy mother of chicken and egg NFS hangs batman"

That was a weird job, fun, it was a local machine room for a warehouse that originally held the IBM mainframe, it still held it's successor "the multiprise 3000" which has the claim to fame as being the smallest mainframe IBM ever sold. But now the room was also full of decades of artisanal crafted unix servers with pick databases. the pick dev team had done most the system architecture. The best way to understand it is that for them pick is the operating system, unix is a necessary annoyance they have to put up with only because nobody has made pick hardware for 20 years. and it was NFS mounts everywhere, somebody had figured out a trick where they could NFS mount a remote machine and have the local pick system reach in and scrounge through the remote systems data. But strictly read-only. pick got grumpy when writing to NFS not to say anything about how the other database would feel about having it's data being messed with. Thus the circular mount.

Still was not the worst thing I saw. I liked the one system with a SMB mount. "Why is this one SMB?" "Well pick complains when you try to write to a NFS mount, but it's NFS detection code does not trip on SMB mounts." ... Sighs "Um... I am no pick expert but you know why it does not like remote mounts right. SMB does not change that, Do you happen to get a lot of corrupt indexes on this machine?" "yes, how did you know"