On Tue, Mar 29, 2011 at 2:09 PM, Andrew Lutomirski <luto@xxxxxxx> wrote:
> I have a disk with a SMART failure. It still works but I assume it'll
> fail sooner or later.
>
> I want to remove it from my btrfs volume, replace it, and add the new
> one. But the obvious command doesn't work:
>
> # btrfs device delete /dev/dm-5 /mnt/foo
> ERROR: error removing the device '/dev/dm-5'
>
> dmesg says:
> btrfs: unable to go below two devices on raid1
>
> With mdadm, I would fail the device, remove it, run degraded until I
> get a new device, and hot-add that device.
>
> With btrfs, I'd like some confirmation from the fs that data is
> balanced appropriately so I won't get data loss if I just yank the
> drive. And I don't even know how to tell btrfs to release the drive
> so I can safely remove it.
>
> (Mounting with -o degraded doesn't help. I could umount, remove the
> disk, then remount, but that feels like a hack.)
There's no "nice" way to remove a failing disk in btrfs right now
("btrfs dev delete" is more of a online management thing to politely
remove a perfectly functional disk you'd like to use for something
else.) As I understand things, the only way to do it right now is the
umount, remove disk, remount w/ degraded, and then btrfs add the new
device.
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