Hallo, Goffredo,

Du meintest am 20.01.11:

To add another disk you don't have to run mkfs.btrfs. For example:

# add the first disk
mkfs.btrfs /dev/sdb
# mount the disk
mount /dev/sdb /media/backups

# add another disk to the first one
btrfs device add /dev/sdc /media/backup

Note1: the filesystem has to be mounted
Note2: the medatada will be in raid1, the data in raid0

Note 3: if the disk has been used (especially under btrfs) you should  
first delete old partitioning data etc:

        dd if=/dev/zero of=/dev/sdb count=1000
        dd if=/dev/zero of=/dev/sdc count=1000

I've just tried your recipe with two devices I had used for other btrfs  
experiments:

        btrfs filesystem show 2>/dev/null

shows my new wishes, and it shows the old settings too.

But writing 1000 blocks seems to be not enough - sometimes I'll try  
bigger numbers. What happens with the old (and now unwanted) settings?

By the way: I nee "2>/dev/null" because the actual git version always  
tries to show all block devices which it finds in "/dev" (no: I don't  
use "udev").

Viele Gruesse!
Helmut