NFS Server hangs on proxmox

I have a proxmox host running BTRFS. I installed debian 8.4 on my server with BTRFS as root filesystem, and then installed proxmox on top of that. This setup runs fine.

Now I’m trying to use this host to export some NFS shares. The shares are visible to remote hosts, but interacting with the NFS shares causes timeouts on the client. I tested this on both Mac OSX and arch linux clients.

Exports:

/var/shares 10.20.0.64(rw,subtree_check,fsid=0)
/var/shares/media 10.20.0.0/24(rw,subtree_check)

Log on arch linux client:

Sep 13 21:53:15 [CLIENT_HOSTNAME] kernel: nfs: server [SERVER_HOSTNAME] not responding, timed out
Sep 13 21:55:01 [CLIENT_HOSTNAME] kernel: nfs: server [SERVER_HOSTNAME] not responding, still trying
Sep 13 21:55:30 [CLIENT_HOSTNAME] kernel: nfs: server [SERVER_HOSTNAME] OK
Sep 13 21:57:48 [CLIENT_HOSTNAME] kernel: nfs: server [SERVER_HOSTNAME] not responding, timed out
Sep 13 21:59:31 [CLIENT_HOSTNAME] kernel: nfs: server [SERVER_HOSTNAME] not responding, still trying
Sep 13 22:00:00 [CLIENT_HOSTNAME] kernel: nfs: server [SERVER_HOSTNAME] OK