2016-03-03 6:57 GMT+02:00 Duncan [off-list ref]:

You're issue isn't the same, because all your space was allocated,
leaving only 1 MiB unallocated, which isn't normally enough to allocate a
new chunk to rewrite the data or metadata from the old chunks into.

That's a known issue, with known workarounds as dealt with in the FAQ.

Ah, thanks, well it was surprising for me that balance failed with out of
space when both data and metadata had not all been used and I thought
it could just use space from those...

especially as from FAQ:

If there is a lot of allocated but unused data or metadata chunks,
a balance may reclaim some of that allocated space. This is the
main reason for running a balance on a single-device filesystem.

so I think regular balance should be smart enough that it could
solve this on own and wouldn't need to specify any options.