On Sun, Feb 26, 2012 at 04:44:00PM +0000, Hugo Mills wrote:
> OK, the real problem you're seeing is that when btrfs removes a
> device from the filesystem, that device is not modified in any way.
> This means that the old superblock is left behind on it, containing
> the FS label information. What you need to do is, immediately after
> removing a device from the FS, zero the first part of the partition
> with dd and /dev/zero.
A correction here: if the device being removed is writable, the
superblock is cleared so it's not recognized as a part of any other fs:
int btrfs_rm_device(struct btrfs_root *root, char *device_path)
...
/*
* at this point, the device is zero sized. We want to
* remove it from the devices list and zero out the old super
*/
if (clear_super) {
/* make sure this device isn't detected as part of
* the FS anymore
*/
memset(&disk_super->magic, 0, sizeof(disk_super->magic));
set_buffer_dirty(bh);
sync_dirty_buffer(bh);
}
Doing this manually means zeroing 4k block at all offsets up to
partition size:
Superblock 0 offset 65536
Superblock 1 offset 67108864
Superblock 2 offset 274877906944
Superblock 3 offset 1125899906842624
Superblock 4 offset 4611686018427387904
david
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