Note for other readers: The parent post probably means incremental ZFS snapshots, which won't store multiple copies of any given block unless the piece of data

Note for other readers: The parent post probably means incremental ZFS snapshots, which won't store multiple copies of any given block unless the piece of data has been moved. ZFS also has a block deduplication scheme, but turning it on is a poor idea. The deduplication table needs to be stored in memory for decent performance, and this takes a lot of memory. Even then, performance is rarely as good as with dedup turned off. It doesn't even save as much space as you'd hope -- it's per-record, and ZFS storage records are 128KiB by default. If you're trying to deduplicate 10KiB files with that, you're going to have a bad time. (Note also: The ZFS record size is dynamic; the 128KiB default is the maximum record size it'll allow, i.e. the most data that has to be read and rewritten (somewhere else) if you modify one byte in a larger file. If you just write a single 10KiB file and force it to disk, then you'll get a 10KiB record. It's complicated; try not to read more into this than "dedup is rarely a good idea," though if I'm allowed a second line, I'll add "compression is always a good idea; enable zle at a minimum.")