NFS mount: Exiting with error EIO

I upgraded my home server from Debian 8 to 9 and afterwards could not mount NFS shares from my Synology Diskstation (running DSM 4.2) anymore:

$ journalctl -x
systemd[1]: mnt-media\x2ddisa.mount: Mount process exited, code=exited status=32
systemd[1]: Failed to mount /mnt/media-disa.
-- Subject: Unit mnt-media\x2ddisa.mount has failed
-- Defined-By: systemd
-- Support:
-- Unit mnt-media\x2ddisa.mount has failed.
-- The result is failed.
kernel: NFS: nfs4_discover_server_trunking unhandled error -22. Exiting with error EIO
systemd[1]: Dependency failed for Remote File Systems.
-- Subject: Unit has failed
-- Defined-By: systemd
-- Support:
-- Unit has failed.
-- The result is dependency.
systemd[1]: Job failed with result 'dependency'.
systemd[1]: mnt-media\x2ddisa.mount: Unit entered failed state.

I found a Fedora bug report that suggested to specify the NFS version that should be used for mounting.

So I edited /etc/fstab and added nfsvers=4 to the mount options, and mounting works since.

disa:/volume2/data  /mnt/data-disa  nfs user,nolock,nfsvers=4

Written by Christian Weiske.

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