On Thu, 27 Feb 2014 12:19:05 -0600
Justin Brown [off-list ref] wrote:

I've a 18 tera hardware raid 5 (areca ARC-1170 w/ 8 3 gig drives) in

Do you sleep well at night knowing that if one disk fails, you end up with
basically a RAID0 of 7x3TB disks? And that if 2nd one encounters unreadable
sector during rebuild, you lost your data? RAID5 actually stopped working 5
years ago, apparently you didn't get the memo. :)
http://hardware.slashdot.org/story/08/10/21/2126252/why-raid-5-stops-working-in-2009

need of help.  Disk usage (du) shows 13 tera allocated yet strangely
enough df shows approx. 780 gigs are free.  It seems, somehow, btrfs
has eaten roughly 4 tera internally.  I've run a scrub and a balance
usage=5 with no success, in fact I lost about 20 gigs after the

Did you run balance with "-dusage=5" or "-musage=5"? Or both?
What is the output of the balance command?

terra:/var/lib/nobody/fs/ubfterra # btrfs fi df .
Data, single: total=17.58TiB, used=17.57TiB
System, DUP: total=8.00MiB, used=1.93MiB
System, single: total=4.00MiB, used=0.00
Metadata, DUP: total=392.00GiB, used=33.50GiB

                       ^^^^^^^^^

If you'd use "-musage=5", I think this metadata reserve should have been
shrunk, and you'd gain a lot more free space.

But then as others mentioned it may be risky to use this FS on 32-bit at all,
so I'd suggest trying anything else only after you reboot into a 64-bit kernel.

-- 
With respect,
Roman