BTRFS balance fails with -dusage=100

Moby
2015-06-23T03:54:19Z

OpenSuSE 13.2 system with single BTRFS / mounted on top of /dev/md1.
/dev/md1 is md raid5 across 4 SATA disks.

System details are:

Linux suse132 4.0.5-4.g56152db-default #1 SMP Thu Jun 18 15:11:06 UTC
2015 (56152db) x86_64 x86_64 x86_64 GNU/Linux

btrfs-progs v4.1+20150622

Label: none uuid: 33b98d97-606b-4968-a266-24a48a9fe50d
Total devices 1 FS bytes used 884.21GiB
devid 1 size 1.36TiB used 889.06GiB path /dev/md1

Data, single: total=885.00GiB, used=883.12GiB
System, DUP: total=32.00MiB, used=144.00KiB
Metadata, DUP: total=2.00GiB, used=1.09GiB
GlobalReserve, single: total=384.00MiB, used=0.00B

Relevant entries from log are:
2015-06-22T22:46:32.238011-05:00 suse132 kernel: [90193.446128] BTRFS:
bdev /dev/md1 errs: wr 9977, rd 0, flush 0, corrupt 0, gen 0
2015-06-22T22:46:32.238050-05:00 suse132 kernel: [90193.446158] BTRFS:
bdev /dev/md1 errs: wr 9978, rd 0, flush 0, corrupt 0, gen 0
2015-06-22T22:46:32.238054-05:00 suse132 kernel: [90193.446179] BTRFS:
bdev /dev/md1 errs: wr 9979, rd 0, flush 0, corrupt 0, gen 0

System was (still is - other than btrfs balance) running fine. Then I
did massive data I/O, copying and deleting and massive amounts of data
to bring the system into it's present state. Once I was done with the
I/O, kicked off btrfs balance start /.
Above command failed. Then I started doing btrfs balance -dusage=XX /
This command succeeds with XX upto and including 99. It fails when I
set XX to 100. btrfs balance also fails if I omit the -dusage option.
The errors in the log make no sense to me since the md raid device is
not reporting any errors at all. Also running btrfs scrub reports no
errors at all.

Any ideas on how to get btrfs balance to succeed without errors would be
welcome.

Regards,

--Moby
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