On Wed, Jan 11, 2012 at 11:37:14AM -0500, Chris Mason wrote:

I've been seeing this as well.  It's new with 3.2, and I haven't yet
been able to track it down.

The first thing that happens when we mount the FS is a block layer
invalidate, and that must be dropping the write.

It's also possible (but very unlikely) that mkfs.btrfs is neglecting to
write that block.

Do you have a reliable way to reproduce?  If so, can you try with a much
older mkfs.btrfs.

I built mkfs from v0.19 and let 209 loop again, the error appeared 6x
during 3 hours, the last 5 occurences within 10 minutes.  Should I try
even older mkfs?

I will try to catch it with blktrace running.

thanks,
david