# 5. Expanding ZFS Pools

Not for everyone but there might come a day that you want to expand your ZFS pools because well, you simply have to much data yourself or you added to many users to it. Then in this section we will show how you could expand your ZFS pool without loosing any of your data. We will do this both for Proxmox and TrueNas ZFS pools.

# 1. Expanding Proxmox ZFS Pool

<span>The</span> <span>consensus</span> <span>among</span> <span>ZFS</span> <span>experts</span> <span>depends</span> <span>on</span> <span>your</span> <span>constraints:</span>

- <span class="font-semibold"><span>If</span> <span>you</span> <span>have</span> <span>spare</span> <span>bays</span> <span>and</span> <span>older</span> <span>drives</span></span><span>:</span> <span>Many</span> <span>recommend</span> <span class="font-semibold"><span>starting</span> <span>replacement</span> <span>earlier</span></span> <span>(around</span> <span>65%</span> <span>full)</span> <span>with</span> <span>one</span> <span>drive</span> <span>at</span> <span>a</span> <span>time,</span> <span>turning</span> <span>the</span> <span>old</span> <span>drive</span> <span>into</span> <span>a</span> <span>spare.</span> [<span class="YviGxtd7YaCspnvhcQVX uHPaz1NVFLwooyN_82Xl ZBCD6edNlK6lCexfhgoI CacXtJfGtE47SYE_l9Hn">practicalzfs.com</span>](https://discourse.practicalzfs.com/t/mirror-pool-expansion-opinions-sought/1822) <span>This</span> <span>keeps</span> <span>your</span> <span>drives</span> <span>fresher</span> <span>and</span> <span>spreads</span> <span>the</span> <span>replacement</span> <span>timeline.</span>
- <span class="font-semibold"><span>If</span> <span>you're</span> <span>space-constrained</span> <span>or</span> <span>prefer</span> <span>simplicity</span></span><span>:</span> <span>The</span> <span>double-resilver</span> <span>approach</span> <span>you</span> <span>mentioned</span> <span>works</span> <span>fine,</span> <span class="font-semibold"><span>especially</span> <span>if</span> <span>you</span> <span>have</span> <span>solid</span> <span>backups</span></span><span>.</span> [<span class="YviGxtd7YaCspnvhcQVX uHPaz1NVFLwooyN_82Xl ZBCD6edNlK6lCexfhgoI CacXtJfGtE47SYE_l9Hn">practicalzfs.com</span>](https://discourse.practicalzfs.com/t/mirror-pool-expansion-opinions-sought/1822)
- <span class="font-semibold"><span>If</span> <span>you're</span> <span>concerned</span> <span>about</span> <span>failure</span> <span>risk</span> <span>during</span> <span>resilvering</span></span><span>:</span> <span>Adding</span> <span>a</span> <span>new</span> <span>vdev</span> <span>is</span> <span>safer</span> <span>since</span> <span>your</span> <span>existing</span> <span>mirror</span> <span>remains</span> <span>intact</span> <span>during</span> <span>the</span> <span>expansion. Then instead of resilvering you could just reconstruct your VM's on your new expanded ZFS pool from a backup. Then once they are running you can turn off your existing VM's on the old storage and eventually delete them. </span>

<span>The</span> <span>key</span> <span>consideration</span> <span>ZFS</span> <span>experts</span> <span>emphasize</span> <span>is</span> <span class="font-semibold"><span>drive</span> <span>age</span></span><span>—mechanical</span> <span>drives</span> <span>typically</span> <span>shouldn't</span> <span>run</span> <span>much</span> <span>longer</span> <span>than</span> <span>a</span> **<span>decade</span>** <span>regardless</span> <span>of</span> <span>health</span> <span>appearance,</span> <span>and</span> <span>running</span> <span>multiple</span> <span>drives</span> <span>while</span> <span>resilvering</span> <span>increases</span> <span>failure</span> <span>risk.</span>

# 2. Expanding TrueNas ZFS Pool