Btrfs devel - Mar 2011 - btrfs fi df gives only the total size that is currently allocated

Hi

I made a test RAID 10 with several old disks with various sizes.
I copied some files (~800MB)
When using btrfs fi df /mountpoint I get
Data: total=1.00GB, used=800.00MB
When I copy another ~800MB I get a total size of 2GB.

This goes on and on until I hit the max size of the RAID.
e.g.
Data: total=5.00GB, used=4.97GB

Is there a way to see what the max size will be without having to fill 
the RAID first?

Thanks,
Gal

P.S. df -h doesn''t help either because of the different disk sizes.
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On Sat, 2011-03-19 at 21:16 +0200, Gal Buki wrote:
> Hi
> 
> I made a test RAID 10 with several old disks with various sizes.
> I copied some files (~800MB)
> When using btrfs fi df /mountpoint I get
> Data: total=1.00GB, used=800.00MB
> When I copy another ~800MB I get a total size of 2GB.
> 
> This goes on and on until I hit the max size of the RAID.
> e.g.
> Data: total=5.00GB, used=4.97GB
> 
> Is there a way to see what the max size will be without having to fill 
> the RAID first?
As I understand it: the simple answer is, unfortunately, “no”. Because
metadata and data chunks are allocated on demand depending on how you
use the space, the best you could do would be to make a guess based on
current allocation ratios.

That is something which is pretty hard to do manually though—
particularly in the case of differently-sized disks—so some sort of
estimation tool could be useful. (But it would be just that: an
estimate, not an exact count.)

This will get worse once btrfs supports having data with different raid
levels on the same filesystem, because you’ll have different amounts of
“available” space depending on which raid type the data in question is
stored with.

-- 
Calvin Walton <calvin.walton@kepstin.ca>

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