From mboxrd@z Thu Jan  1 00:00:00 1970
From: Adam Nielsen <a.nielsen@shikadi.net>
Subject: Re: OSD::mkfs: couldn't mount FileStore: error -22
Date: Mon, 15 Oct 2012 09:19:35 +1000
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References: <k5dqro$s4d$1@ger.gmane.org> <507B2E71.4040706@inktank.com>
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> The immediate cause of the problem is that the osd's "commit_op_seq" file is
> reading back '0',
> which is invalid; it's created with an initial value of 1.  Try removing the
> osd data dir
> (/var/lib/ceph/osd/ceph-0) completely and let it be recreated; perhaps
> something got there somehow by mistake.

Well it looks like commit_op_seq was never created properly:

$ ls /var/lib/ceph/osd/ceph-0/current/
total 4.0K
drwxr-xr-x 1 root root 26 Oct 14 17:40 .
drwxrwx--- 1 root root 74 Oct 14 17:40 ..
-rw-r--r-- 1 root root  0 Oct 14 17:40 commit_op_seq

But how do I delete it to start again?

$ rm -rf current/
rm: cannot remove `current': Directory not empty
$ ls current/
total 4.0K
drwxr-xr-x 1 root root  0 Oct 15 09:16 .
drwxrwx--- 1 root root 26 Oct 15 09:16 ..

This is on a brand new btrfs filesystem mounted in /var/lib/ceph/osd/ceph-0. 
I created it with this:

$ mkfs.btrfs -L data -s 4096 /dev/sda1

Did I do something wrong?

Thanks,
Adam.