Would this only happen if the drives hadn't been prepared with the builder images (i.e., they were partitioned and formatted by hand)?

Good question. It's quite possible that we've upgraded the builder image over the years, or even that we use mke2fs in a mode whereby it chooses the block size based on the partition size.

The Right Thing, which I've no idea whether we do, is to use big block sizes (4K) for music partitions, as almost 50% of files are much, much bigger than that and it saves space on the block-in-use bitmaps, indirect blocks, and so on.

Peter