Re: [PATCH][BTRFS-PROGS] Enhance btrfs fi df

[Hugo Mills <hugo@carfax.org.uk>]

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On Fri, Nov 02, 2012 at 07:05:37PM +0000, Gabriel wrote:
> On Fri, 02 Nov 2012 13:02:32 +0100, Goffredo Baroncelli wrote:
> > On 2012-11-02 12:18, Martin Steigerwald wrote:
> >> Metadata, DUP is displayed as 3,50GB on the device level and as 1,75GB
> >> in total. I understand the logic behind this, but this could be a bit
> >> confusing.
> >> 
> >> But it makes sense: Showing real allocation on device level makes
> >> sense,
> >> cause thats what really allocated on disk. Total makes some sense,
> >> cause thats what is being used from the tree by BTRFS.
> > 
> > Yes, me too. At the first I was confused when you noticed this
> > discrepancy. So I have to admit that it is not so obvious to understand.
> > However we didn't find any way to make it more clear...
> > 
> >> It still looks confusing at first…
> > We could use "Chunk(s) capacity" instead of total/size ? I would like an
> > opinion from a "english people" point of view..
> 
> This is easy to fix, here's a mockup:
> 
> Metadata,DUP: Size: 1.75GB ×2, Used: 627.84MB ×2
>    /dev/dm-0        3.50GB

   I've not considered the full semantics of all this yet -- I'll try
to do that tomorrow. However, I note that the "×2" here could become
non-integer with the RAID-5/6 code (which is due Real Soon Now). In
the first RAID-5/6 code drop, it won't even be simple to calculate
where there are different-sized devices in the filesystem. Putting an
exact figure on that number is potentially going to be awkward. I
think we're going to need kernel help for working out what that number
should be, in the general case.

   Again, I'm raising minor points based on future capabilities, but I
feel it's worth considering them at this stage, even if the correct
answer is "yes, we'll do this now, and deal with any other problems
later".

   Hugo.

>            Data   Metadata Metadata    System System              
>            Single Single   DUP         Single DUP         Unallocated
>                                                                
> /dev/dm-16 1.31TB   8.00MB  56.00GB    4.00MB  16.00MB           0.00
>            ====== ======== =========== ====== =========== ===========
> Total      1.31TB   8.00MB  28.00GB ×2 4.00MB   8.00MB ×2        0.00
> Used       1.31TB     0.00   5.65GB ×2   0.00 152.00KB ×2            
> 
> Also, I don't know if you could use libblkid, but it finds more 
> descriptive names than dm-NN (thanks to some smart sorting logic).
> 
> 

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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  --- My doctor tells me that I have a malformed public-duty gland, ---  
                and a natural deficiency in moral fibre.                 

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