add options nolock in /etc/pve/storage.cfg
[FONT=Arial, Tahoma, Helvetica, FreeSans, sans-serif]here is the example
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nfs: nfs104_iso
path /mnt/pve/nfs104_iso
server 1.1.1.104
export /mnt/vm_data/ISO
options nolock
content iso
reboot or
/etc/init.d/rpcbind restart
/etc/init.d/nfs-common restart
