On Thu 20 January 2011 22:55:54 Hubert Kario wrote:

You still have a btrfs on /dev/sdc, do a 
dd if=/dev/zero of=/dev/sdc bs=8192
(overkill, but I don't remember which blocks have to be zeroed to destroy 
btrfs superblock)

I gave up and started over.  Maybe it should be clarified in the wiki that no mkfs should be done on additional volumes, as it's counterintuitive to some.

yes. rc.local is too late, unless you will also mount the volume from there 
and not using /etc/fstab

How and when then?

That depends - it has to be done before mounting. And if the device is
part of the boot partition then you may put the "scan" command into an
init-ramdisk.

This does not seem to have been sent to the listserv, as I only got it in a reply.  This is likely incomplete.

Using something like "device=/dev/sdb,device=/dev/sdc" on fstab mount
options should also work.

You mean as a substitute for a scan?

On my other server the btrfs array seems to mount just fine without any measures to scan.  I don't understand this,  nor why no specific advice is given about scanning on boot in the wiki.