Consider a subnet of about 30 Windows workstations in a Windows domain and a Synology NAS.
When browsing the mapped NAS file system as a network drive in Windows File Explorer, it usually works pretty nicely, but sometimes opening a folder hangs for a long time and the Windows address bar shows the green progress indicator loading. It's not a specific folder. Could be just about any random folder. All load statistics on the NAS look ok and when measuring the bandwidth with iperf even during a hang-up, everything's as expected in a gigabit network. Everything from the NAS seems to be served from the SSD cache, so the HDDs don't even seem to be touched very often.
When analyzing the hang-up with Wireshark, there's an SMB2 Create Request File for the folder in question and some 30 secs later there's a Create Response File with STATUS_SUCCESS. Between these requests I can see a bunch of IPA Unknown 0x52 and RSL unknown 0 from the NAS to the connecting client, but these are pretty much the only thing that looks out of place to me.
I've tried messing with Opportunistic Lock / Lease settings in the Synology SMB settings but that doesn't seem to affect much.
I've also done a switch port mirror for the NAS to check out if it's maybe waiting for authentication from a Domain Controller or something else, but couldn't see anything relevant.
None of the network equipments seem to be overloaded either. There are a bunch of HP switches involved.
Any ideas of further things to check or further info I could provide?
