On Thu, Jun 23, 2016 at 03:10:09AM +0200, Hans van Kranenburg wrote:

On 06/22/2016 07:26 PM, David Sterba wrote:

quoted

From: David Sterba <redacted>

Hi,

the chunk dump is a useful thing, for debugging or balance filters.

Example output:

Chunks on device id: 1
PNumber            Type        PStart        Length          PEnd     Age         LStart  Usage
-----------------------------------------------------------------------------------------------
      0   System/RAID1        1.00MiB      32.00MiB      33.00MiB      47        1.40TiB   0.06
      1 Metadata/RAID1       33.00MiB       1.00GiB       1.03GiB      31        1.36TiB  64.03
      2 Metadata/RAID1        1.03GiB      32.00MiB       1.06GiB      36        1.36TiB  77.28
      3     Data/single       1.06GiB       1.00GiB       2.06GiB      12      422.30GiB  78.90
      4     Data/single       2.06GiB       1.00GiB       3.06GiB      11      420.30GiB  78.47
...

On RAID0, it looks funny :)

# ./btrfs inspect-internal dump-chunks /mnt/extents/
Chunks on device id: 1
PNumber            Type        PStart        Length          PEnd Age         LStart
----------------------------------------------------------------------------------------
       0 Metadata/RAID0        1.00MiB     256.00MiB     257.00MiB 1       13.36GiB
       .           empty             .      16.00EiB             .  .              .
       1   System/RAID0      129.00MiB      64.00MiB     193.00MiB 2       13.61GiB
       .           empty             .      16.00EiB             .  .              .
       2     Data/RAID0      161.00MiB       2.00GiB       2.16GiB 3       15.68GiB
       .           empty             .     115.00MiB             .  .              .
       3     Data/RAID0        2.27GiB       2.00GiB       4.27GiB 0       11.36GiB

Chunks on device id: 2
PNumber            Type        PStart        Length          PEnd 
Age         LStart
----------------------------------------------------------------------------------------
       0     Data/RAID0        1.00MiB       2.00GiB       2.00GiB 0       11.36GiB
       .           empty             .      16.00EiB             .  .              .
       1 Metadata/RAID0        1.00GiB     256.00MiB       1.25GiB 1       13.36GiB
       .           empty             .      16.00EiB             .  .              .
       2   System/RAID0        1.13GiB      64.00MiB       1.19GiB 2       13.61GiB
       .           empty             .      16.00EiB             .  .              .
       3     Data/RAID0        1.16GiB       2.00GiB       3.16GiB 3       15.68GiB

For the correct sizes, it would be needed to either do some math, like 
if RAID0 then divide by 2, but I guess this gets horrible really soon 
with RAID5 etc... Or, if you want to print everything in the physical 
order, why not just dump the device tree with DEV_EXTENT which has the 
exact length on disk, and fill in the missing information using the 
reference to the chunk they belong to?

That's a good idea and would avoid the guesswork that makes the current
numbers funny.