[fc417fc802]

Which is exactly why you periodically do maintenance to compact the free space. Thus it isn't an issue in practice unless you have a very specific workload in which case you should probably be using a specialized solution. (Although I've read that apparently you can even get a workload like postgres working reasonably well on zfs which surprises me.)

If things get to the point where there's over 1 TB of fragmented free space on a filesystem that is entirely the fault of the operator.

[kbolino]

What argument are you driving at here? The smaller the free space, the harder it is to run compaction. The larger the free space, the easier it is. There are some confounding forces in certain workloads, but the general principle stands.

"Your free space shouldn't be very fragmented when you have such large amounts free!" is exactly why you should keep large amounts free.