Re: [RFC][PATCH] btrfs-progs: inspect: new subcommand to dump chunks

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On Thu, Jun 23, 2016 at 03:10:09AM +0200, Hans van Kranenburg wrote:
> On 06/22/2016 07:26 PM, David Sterba wrote:
> > From: David Sterba <dsterba@xxxxxxx>
> >
> > 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.
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