Description of problem:

mkfs a btrfs with RAID1 on many devices failed. No matter metadata or data is RAID1, as long as there's RAID1 profile specified.

mkfs -t btrfs -m raid1 -d raid1 -f /dev/loop0 /dev/loop2 ... /dev/loop49
mkfs.btrfs: volumes.c:852: btrfs_alloc_chunk: Assertion `!(ret)' failed.

WARNING! - Btrfs v0.20-rc1 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

adding device /dev/loop1 id 2
adding device /dev/loop2 id 3
adding device /dev/loop3 id 4
adding device /dev/loop4 id 5
adding device /dev/loop5 id 6
adding device /dev/loop6 id 7
adding device /dev/loop7 id 8
adding device /dev/loop8 id 9
adding device /dev/loop9 id 10
adding device /dev/loop10 id 11
adding device /dev/loop11 id 12
adding device /dev/loop12 id 13
adding device /dev/loop13 id 14
adding device /dev/loop14 id 15
adding device /dev/loop15 id 16
adding device /dev/loop16 id 17
adding device /dev/loop17 id 18
adding device /dev/loop18 id 19
adding device /dev/loop19 id 20
adding device /dev/loop20 id 21
adding device /dev/loop21 id 22
adding device /dev/loop22 id 23
adding device /dev/loop23 id 24
adding device /dev/loop24 id 25
adding device /dev/loop25 id 26
adding device /dev/loop26 id 27
adding device /dev/loop27 id 28
adding device /dev/loop28 id 29
adding device /dev/loop29 id 30
adding device /dev/loop30 id 31
adding device /dev/loop31 id 32
adding device /dev/loop32 id 33
adding device /dev/loop33 id 34
adding device /dev/loop34 id 35
adding device /dev/loop35 id 36
adding device /dev/loop36 id 37
adding device /dev/loop37 id 38
adding device /dev/loop38 id 39
adding device /dev/loop39 id 40
adding device /dev/loop40 id 41
adding device /dev/loop41 id 42
adding device /dev/loop42 id 43
adding device /dev/loop43 id 44
adding device /dev/loop44 id 45
adding device /dev/loop45 id 46
adding device /dev/loop46 id 47
adding device /dev/loop47 id 48
adding device /dev/loop48 id 49
adding device /dev/loop49 id 50

Version-Release number of selected component (if applicable):
btrfs-progs-0.20.rc1.20130917git194aa4a-1.el7

How reproducible:
always

Steps to Reproduce:
1. see description
2.
3.

Actual results:


Expected results:


Additional info: