On Tue, Aug 30, 2016 at 10:22:24AM +0000, ojab // wrote:

On Mon, Aug 29, 2016 at 9:05 PM, Chris Murphy [off-list ref] wrote:

quoted

On Mon, Aug 29, 2016 at 10:04 AM, ojab // [off-list ref] wrote:
What do you get for 'btrfs fi us <mp>'

$ sudo btrfs fi us /mnt/xxx/
Overall:
    Device size:                  3.64TiB
    Device allocated:             1.82TiB
    Device unallocated:           1.82TiB
    Device missing:                 0.00B
    Used:                     1.81TiB
    Free (estimated):             1.83TiB         (min: 943.55GiB)
    Data ratio:                  1.00
    Metadata ratio:                  2.00
    Global reserve:             512.00MiB         (used: 0.00B)

Data,RAID0: Size:1.81TiB, Used:1.80TiB
   /dev/sdb1        928.48GiB
   /dev/sdc1        928.48GiB

Metadata,RAID1: Size:3.00GiB, Used:2.15GiB
   /dev/sdb1          3.00GiB
   /dev/sdc1          3.00GiB

System,RAID1: Size:32.00MiB, Used:176.00KiB
   /dev/sdb1         32.00MiB
   /dev/sdc1         32.00MiB

Unallocated:
   /dev/sdb1          1.01MiB
   /dev/sdc1          1.00MiB
   /dev/sdd1          1.82TiB

   Basically, your FS is full. Note that replacing just one of the
devices in a RAID-0 array with a larger one is not going to help. What
you really need here is "single", not RAID-0. I would probably try
converting to single first (which should move quite a lot of it to the
new device anyway), and then the device delete:

 btrfs balance start -dconvert=single,soft /mountpoint
 btrfs dev delete /dev/sdc1 /mountpoint

   Hugo.

quoted

You can see what the state of block groups are with btrfs-debugfs
which is in kdave btrfs-progs git. Chances are you need a larger
value, -dusage=15 -musage=15 to free up space on devid 1 and 2. Then
maybe devid 3 can be removed.

btrfs-debugfs output:
https://gist.github.com/ojab/a3c59983e8fb6679b8fdc0e88c0c9e60
Before `delete` the was about 60Gb of free space, looks like it was
filled during `delete` (I've seen similar behavior during `btrfs fi
defrag`) and I should use `-dusage=69` and up.

I don't quite understand what exactly btrfs is trying to do: I assume
that block groups should be relocated to the new/empty drive, but
during the delete `btrfs fi us` shows
Unallocated:
/dev/sdc1         16.00EiB

so deleted partition is counted as maximum possible empty drive and
blocks are relocated to it instead of new/empty drive? (kernel-4.7.2 &
btrfs-progs-4.7.1 here)
Is there any way to see where and why block groups are relocated
during `delete`?

//wbr ojab

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