It’s not exactly difficult to figure out how much space you’ve got left when you’re using OpenZFS–but it is different from doing so on traditional filesystems, as OpenZFS brings considerably more complexity to the table. Space accounting in OpenZFS requires a different approach due to factors like snapshots, compression, and deduplication.

By the time we’re done today, we’ll understand:

• how to use both filesystem-agnostic tools like du and df

• OpenZFS-native tools like zfs list and zpool list.

OpenZFS brings new concepts to filesystem management that muddy this simple picture a bit: snapshots, inline compression, and block-level deduplication. To effectively manage our OpenZFS filesystem, we’ll need to begin by understanding three properties: USED, REFER, and AVAIL.

All three properties revolve around the status of logical sectors, not physical sectors.