[CentOS] LVM + XFS + external log + snapshots

Hi all,

So I have an XFS file system within LVM  which has an external log.

My mount option in FSTAB is;

/dev/vg_spock_data/lv_data	/data	xfs	logdev=/dev/sdc1,nobarrier,logbufs=8,noatime,nodiratime	1 1

All is well no issues and very fast.

Now I'd like to snapshot this bad boy and then run rsnapshot to create a few days backup.

A snapshot volume is created w/o issue;

lvcreate -L250G -s -n datasnapshot /dev/vg_spock_data/lv_data

But when i try to mount the file system;

mount /dev/vg_spock_data/datasnapshot /snapshot -o nouuid,ro

I get this;

mount: wrong fs type, bad option, bad superblock on /dev/mapper/vg_anette_data-datasnapshot,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

The command dmesg shows;

XFS (dm-3): filesystem is marked as having an external log; specify logdev on the mount command line.
XFS (dm-3): SB validate failed

So I then use this mount option;

mount /dev/vg_anette_data/datasnapshot /snapshot -o logdev=/dev/sdc1,nouuid,ro

But get this error;

mount: /dev/mapper/vg_spock_data-datasnapshot already mounted or /snapshot busy

And the command dmesg shows;

XFS (dm-3): Invalid device [/dev/sdc1], error=-16

Am I doing something wrong or is this not possible?

I prefer being in error, I often am anyways.

Thanks in advance,

- aurf