Extending a Storage Pool

How to add additional storage to an existing pool

  2 minute read

There are numerous options available to TrueNAS users for extending pools within a system. They are:

  • Data
  • Cache
  • Log
  • Hot Spare
  • Metadata
  • Dedup

For the purposes of this article, the focus will be on adding a data vdev to an existing pool.


When adding disks to increase the capacity of a pool, ZFS supports the addition of virtual devices, or vdevs, to an existing ZFS pool. To extend a pool, the vdev being added must be the same type as the existing vdevs. The ADD VDEVS button is only enabled when the vdev being added is the same type as the existing vdevs. Examples are as follows:

  • To extend a Stripe, any number of available disks may be chosen
  • To extend a two-drive ZFS mirror, add another two drives
  • To extend a three-drive RAIDZ1, add another three drives
  • To extend a four-drive RAIDZ2, add another four drives

Mixing disks of different sizes in a vdev is not allowed. For example, if you have a mirrored pool with two 3TB drives, the added disks must also be 3TB.

For encrypted pools, the added disks will inherit the same encryption options as the parent disks (encryption key/passphrase).

Before creating a pool, determine the level of required redundancy, how many disks will be added, and if any data exists on those disks. Creating a pool/adding vdevs overwrites disk data, so save any required data to different media before adding disks/vdevs to a pool.


Go to Storage > Pools and select the   of the pool you want to extend. From the dropdown select Add Vdevs. This will take you to the Pool Manager page.

Select the appropriate number of disks needed to extend the pool under Available Disks. Click on the arrow to add those disks to the Data VDevs section.

Ensure the number of disks that you add matches the type of vdev (Stripe/Mirror/RaidZ1 etc.).

Once you have selected the appropriate number of disks, click ADD VDEVS. A dialog box will appear, check Confirm and click ADD VDEVS.

Once the process is complete, you will be taken to the Storage/Pools page. To verify your disk(s) were added successfully select the   and choose status from the dropdown menu. This will take you to the Storage/Pools/Pool Status page. Here you can verify your vdevs have been successfully added.

Last modified November 13, 2020: Update ExtendPool.md (db236a1c)