btrfs raid1 still recognized after being overwritten by md raid1

I created an md raid1 on partitions that had a btrfs raid1, but btrfs is still recognized on one of those partitions. (Is it finding some left-over, redundant metadata?) I'm concerned this will confuse me or btrfs in the future. How should I fix this?

Details: after installing on btrfs for the first time, I created a btrfs raid1 in Fedora 13 on sda7 sdb7. Then, while reinstalling Fedora 13 from DVD, I created an md raid1 on those partitions, containing / type ext4. After booting onto that /, btrfs is still recognized on sda7, but sda7 is also in md7, which is mounted on / as type ext4:

[root@pikake jdb]# cat /proc/mdstat Personalities : [raid1]
md127 : active (auto-read-only) raid1 sdb5[1] sda5[0] 204788 blocks super 1.0 [2/2] [UU]

md8 : active raid1 sda8[0] sdb8[1]
218100 blocks super 1.0 [2/2] [UU]

md7 : active raid1 sda7[0] sdb7[1]
48820156 blocks super 1.1 [2/2] [UU]
bitmap: 1/1 pages [4KB], 65536KB chunk

md3 : active raid1 sda3[0] sdb3[1]
12287936 blocks [2/2] [UU]

unused devices: <none>
[root@pikake jdb]# btrfs-show
failed to read /dev/sdf
failed to read /dev/sde
failed to read /dev/sdd
failed to read /dev/sdc
failed to read /dev/sr0
Label: none uuid: 3257ab1a-45de-43d3-bd84-a01ca93d0296 Total devices 1 FS bytes used 7.71GB
devid 1 size 48.83GB used 14.54GB path /dev/sda6

Label: none uuid: c25ab51a-9fec-4e67-a5d8-4968e7d2e5e8 Total devices 2 FS bytes used 7.69GB
devid 1 size 46.56GB used 11.40GB path /dev/sda7 *** Some devices missing

Btrfs Btrfs v0.19
[root@pikake jdb]# mount
/dev/md7 on / type ext4 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620) tmpfs on /dev/shm type tmpfs (rw,rootcontext="system_u:object_r:tmpfs_t:s0") /dev/md8 on /boot type ext4 (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw) sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw) gvfs-fuse-daemon on /home/jdb/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=jdb)

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Quoted 4 lines · J. David Beutel

I created an md raid1 on partitions that had a btrfs raid1, but btrfs is still recognized on one of those partitions. (Is it finding some left-over, redundant metadata?) I'm concerned this will confuse me or btrfs in the future. How should I fix this?

Seem that btrfs-show checks the 1st superblock only, running the following can zap some part of that superblock,

dd if=/dev/zero of=/dev/sda7 seek=128 bs=512 count=1

but probably, you need to zap the 2nd superblock as

dd if=/dev/zero of=/dev/sda7 seek=128k bs=512 count=1

In case the block is being used, you can dump that block and search "_BHRfS_M" in that block before clear it.