NFS export an overlay of ext4 and btrfs
Solution 1:
From kernel.org and from dmesg while trying to reproduce the error you also have to specify
-
-o index=on -
-o index=on -o redirect_dir=nofollowwhen there is noupperdir
Your mount command then should be as follows.
mount -t overlay overlay -o lowerdir=/mnt/raid/folder1/:/mnt/ext4/folder1 -o comment=merge -o nfs_export=on -o index=on -o redirect_dir=nofollow /data/merged
The output of
/sys/module/overlay/parameters/nfs_export:N
shows the default of the mountoption and verifies that it is actually available.