Pools

To create a new pool, go to Storage and click Create Pool.

First, enter a pool name.

Next, configure the virtual devices (vdevs) that make up the pool.

If the disks used have non-unique serial numbers, they do not populate the Available Disks section until the Show disk with non-unique serial numbers checkbox is selected.

Clicking Suggest Layout allows TrueNAS to review all available disks and populate the primary Data VDevs with identically sized drives in a configuration balanced between storage capacity and data redundancy. Click Reset Layout to clear the suggestion.

To manually configure the pool, add vdevs according to your use case. Check the Disk checkboxes and click the   to move the disks into a vdev.

Warning: USB-connected disks may report their serial numbers inaccurately, making them indistinguishable from each other.

Pools offer several vdev types. Vdevs store data or enable unique features for the pool.

To add a vdev type during pool creation, click Add Vdev() and select the type. Select disks from Available Disks and use the   (right arrow) next to the new VDev to add it to that section.

Data is the standard vdev for primary storage operations. Each storage pool requires at least one Data vdev. Data vdev configuration typically affects how users can configure other types of vdevs.

• Cache: ZFS L2ARC read-cache used with fast devices to accelerate read operations. Users can add or remove Cache VDevs after creating the pool.
• Log: ZFS LOG device that improves synchronous write speeds. Users can add or remove Log VDevs after creating the pool.
• Hot Spare: Drives reserved for inserting into Data vdevs when an active drive fails. The system uses hot spares as temporary replacements for failed drives to prevent larger pool and data loss scenarios. When a user replaces a failed drive with a new one, the hot spare reverts to an inactive state and becomes available again as a hot spare. If a user detaches the failed drive from the pool without adding a new one, the system promotes the temporary hot spare to a full Data vdev member.
• Metadata: Special allocation class used to create Fusion Pools for increased metadata and small block I/O performance.
• Dedup: Stores ZFS de-duplication. Requires allocating X GiB for every X TiB of general storage. Example: 1 GiB of Dedup vdev capacity for every 1 TiB of Data vdev availability.

Disks added to a vdev arrange in different layouts, according to the specific pool use case.

The Pool Manager suggests a vdev layout from the number of disks added to the vdev. For example, if you add two disks, TrueNAS automatically configures the vdev as a Mirror. The total available storage is the size of one added disk while the other disk provides redundancy.

To change the vdev layout, open the Data VDevs list and select the desired layout.

• Stripe: Each disk stores data. A Stripe requires at least one disk and has no data redundancy.
• Mirror: Data is identical in each disk. A Mirror requires at least two disks, provides the most redundancy, and has the least capacity.
• RAIDZ1: Uses one disk for parity while all other disks store data. RAIDZ1 requires at least three disks.
• RAIDZ2: Uses two disks for parity while all other disks store data. RAIDZ2 requires at least four disks.
• RAIDZ3: Uses three disks for parity while all other disks store data. RAIDZ3 requires at least five disks.

Never use Stripe to store critical data! A single disk failure results in losing all data in the vdev.

The import procedure only applies to disks with a ZFS storage pool. To import disks with different file systems, see the SCALE Disks article.

ZFS pool importing works for pools that were exported or disconnected from the current system, created on another system, and pools to reconnect after reinstalling or upgrading the TrueNAS system.

To import a pool, go to Storage and click Import.

TrueNAS detects any pools that are present but unconnected.

Select a pool from the Pool drop-down and click Next.

Review the Pool Import Summary and click Import.

Pool Options allows users to set/unset Auto TRIM.

With Auto TRIM selected and active, TrueNAS periodically checks the pool disks for storage blocks it can reclaim. Auto TRIM can impact pool performance, so it’s disabled by default.

For more details about TRIM in ZFS, see the autotrim property description in zpool.8.

The Export/Disconnect option disconnects the pool to transfer drives to a new system for importing or completely deletes the pool and any data stored on it.

A dialog box displays any system services affected by exporting the pool.

Users can erase all data on the pool by checking the Destroy data on this pool? box.

Clicking the Delete configuration of shares that used this pool? box deletes shares connected to the pool.

The Add Vdevs button opens the Pool Manager so users can add Vdevs to the pool.

Users cannot change the original encryption or data Vdev configuration.

TrueNAS selects Data VDev by default. To add different Vdev types to the pool, select one from the Add Vdev drop-down.

When adding disks to increase the capacity of a pool, ZFS supports adding Vdevs (virtual devices) to an existing ZFS pool. After creating a Vdev, you cannot add more drives to that Vdev. However, you can stripe a new Vdev with another of the same type to increase the overall pool size To extend a pool, you must add a Vdev that is the same type as existing Vdevs.

Vdevs extending examples:

• To make a striped mirror, add the same number of drives to extend a ZFS mirror. For instance, if ten new drives are available, you could initially create a mirror of two drives, then extend the mirror by adding another mirror of two drives, repeating three more times until you’ve added all ten drives.
• To make a stripe of two RAIDZ1 Vdevs (similar to RAID 50 on a hardware controller), add another three drives to extend a three-drive RAIDZ1.
• To make a stripe of RAIDZ2 vdevs (similar to RAID 60 on a hardware controller), add another four drives to extend a four-drive RAIDZ2.
• Add a disk as a Hot Spare to the pool.

Scrub Pool initiates a pool data integrity check.

If TrueNAS detects any problems during the scrub, it either corrects them automatically or generates an alert in the web interface.

By default, TrueNAS automatically checks every pool is on a reoccurring scrub schedule.

Status displays the state of the last scrub and disks in the pool.

The Pool Status screen has additional disk management options.

The Upgrade Pool option only appears when TrueNAS can upgrade the pool to use new ZFS feature flags.

Before upgrading an existing pool, be aware of these caveats:

• Upgrading a pool is one-way. You cannot regress to an earlier ZFS version or downgrade to an earlier software version that does not support those ZFS features.
• Upgrading a pool unlikely affects data, but we recommend backing up data for safety. Before performing any operation that can affect the data on a storage disk, always back up all data first and verify the backup’s integrity.
• Upgrading a ZFS pool is optional. Do not upgrade the pool if you may revert to an earlier TrueNAS version or repurpose the disks in another OS that supports ZFS. Upgrading a pool is unnecessary unless the end-user specifically needs the newer ZFS Feature Flags. If you upgrade a pool to the latest feature flags, you cannot import it into another OS that does not yet support them.

Upgrading a pool only takes a few seconds and is non-disruptive. You do not need to stop any sharing services to upgrade a pool. However, we recommend upgrading when the pool is not seeing heavy use. Upgrading suspends I/O for a short period, but is nearly instantaneous on a quiet pool.