With ZFS you have two (soon to be three) options for expanding without buying the drives upfront: 1. Add more vdevs. For example, you can start with a pair of

With ZFS you have two (soon to be three) options for expanding without buying the drives upfront: 1. Add more vdevs. For example, you can start with a pair of drives in a mirror. Then when you need more space, you can add another pair of drives in a mirror and add that mirror to your pool. This way lets you smoothly increase your available space over time but you do end up with half your drives being parity while still potentially suffering a data loss if two drives in a mirror break at the same time. 2. Replace all of your drives with larger drives (one at a time so the pool can resilver the data onto the drive). This is nice because you can do it as your old drives fail, but the new space won't be available until all drives have been replaced. 3. There is a feature under development for raidz expansion. (Raidz is like raid5/6). The work on the alpha is up at: https://github.com/openzfs/zfs/pull/8853 https://github.com/openzfs/zfs/pull/8853