certain filesystems cannot be used as chunkstores, because they don't
support 2^16 subdirectories (e.g. ext4 with certain features disabled
or ext3 - see ext4(5))
reported via our community forum:
https://forum.proxmox.com/threads/emlink-too-many-links.73108/
Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>