It turns out that moving files from traditional volumes to flexible volumes makes them "grow", in the sense that they have more index blocks, as accounted in "ls -s" output, and charged against quotas. I think it's a bit sneaky of NetApp to have done this without mentioning it in their conversion documents.

Executive summary: disk block addresses in inodes and in index blocks have changed from 4-byte to 8-byte objects. (That's conjecture, of course, but it seems to explain the observed effects.)

Files <= 64 bytes use no blocks (that is unchanged). Files <= 32 KB (used to be 64 KB) use ceil(size/4KB) data blocks only, no index blocks. Files up to c. 2 MB (used to be 4 MB) use ceil(size/4KB) data blocks and one 4 KB index block Files up to c. 4 MB (used to be 8 MB) use ceil(size/4KB) data blocks and two 4 KB index blocks ...

The main expansion effect comes from files in the 32KB+1 to 64KB size range, where the extra index block is a significant proportion of the total.

Has anyone worked out the new formulae in nit-picking detail? I say "c. 2 MB" above because the transition actually occurs a few blocks before 2 MB: I think there may be some overhead in the index blocks so that not quite 512 addresses will fit in them.