I have a VMware ESXi lab in my home using two physical hosts and a Synology NAS device. I've been using this for some years now without issue. I am setting up a newer lab on two ESXi "hosts" that I'm running on my Mac using VMware Fusion. I set this up the other day and created the VCA on the Synology datastore and it was working just fine. The only issue I had was speed since my Mac and the two new hosts are living in one part of my house and the Synology device is in the basement connected by a wireless network. While it ran OK, it was obviously a little slow and I decided to move the Synology box to the GB connection near my Mac. There is no routing going on here... it's all one big happy network and the wireless devices just create a mesh network to connect everything together in my house.
Before I moved the Synology box, I noticed that I was woefully behind on my updates so I applied all of the waiting updates. I didn't notice what version of DSM I was on before I started, but I'm on 6.1 now. After I did that and moved the box, I fired everything back up on the new lab and that's when the problems began. The hosts recognize the iSCSI setup and it sees the Synology device and the Synology device sees the iSCSI connections from the lab, but it no longer sees the datastore. I've tried doing everything i can think of in the ESXi environment to get the datastore back and nothing works. I even took the box back to the basement and fired up the old lab and it also fails to see the datastore. I haven't done anything to delete or screw with the datastore that I know of and I'd really like to be able to get this running again without having to completely rebuild the lab.