On 2015-08-31 14:11, Theodore Ts'o wrote:
> On Sun, Aug 30, 2015 at 08:16:21PM +0530, Chandan Rajendra wrote:
>> For small filesystem instances (i.e. size <= 1 GiB), mkfs.btrfs fails when
>> "data block size" does not match with the "metadata block size" specified on
>> the mkfs.btrfs command line. This commit increases the size of filesystem
>> instance created so that the test can be executed on subpagesize-blocksize
>> Btrfs instances which have different values for data and metadata blocksizes.
>
> Stupid question --- why isn't this considered a bug in mkfs.btrfs?
> Does btrfs simply not support file systems <= 1 GB?  So if someone has
> a 1GB USB disk or SD card, what's the official advice from the btrfs
> developers?  Use xfs or ext4?
AFAIK, it shouldn't be failing that way, and should automatically switch 
to mixed mode allocation.  A 1G filesystem should work fine for BTRFS, 
but smaller ones will have higher chances of ENOSPC issues (inversely 
proportional to the size of the FS).  I would advise against using BTRFS 
on such a small disk (I avoid using it on anything smaller than 4G 
personally), but I'm not one of the developers, and the fact that I feel 
it isn't a good idea doesn't mean it shouldn't work.