[Btrfs-users] Requirements for btrfs

[Chris mason]

On Thursday 17 January 2008, Otto Muller wrote:
> Hi,
>
> i've just tested btrfs-0.10.
> when i copyed my portage on btrfs volume, a have such
> bug:
>
> ------------[ cut here ]------------
> kernel BUG at
> /home/muller/btrfs/btrfs-0.10/extent-tree.c:1651!
> invalid opcode: 0000 [#1] PREEMPT SMP
> Modules linked in: btrfs xt_mac xt_limit xt_multiport
> ipt_owner ipaq usbserial nvidia(P)

[Oops due to out of space]
>
> i allready figured out that minimal filesystem size is
> 256mb, and i noticed that btrfs can crash if
> filesystem is "full".
> my filesystem is 500mb large, and after crash it still
> have 15mb free :)
>
> is it such "full" to crash? and what are current
> required minimal free size for "stable" work?
>
> and btw, are such reports about crashes needed? or on
> this stage of development this is odd?

Sorry, how big was your partition?  I haven't tested fully the minimum FS 
size, but it also varies with how many blocks you plan on changing during a 
transaction.  So you could have a 256MB partition if you only change a small 
number of things, but it would run out of space if you constantly rewrote a 
256MB file.

This is because the transactions are snapshot based.  So, you need to have 
enough room for the old copy of any blocks you modify during a commit and the 
new copy.

-chris