TrueNAS SCALETrueNAS SCALE Nightly Development Documentation
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The zvol screens and widgets, accessed from the Datasets screen, allow you to add or edit a zvol and manage the volume storage. Like datasets, zvols are listed on the Datasets screen tree table.


The tree table includes storage space used and available for that zvol (or dataset), encryption status (locked, unlocked, or unencrypted), and the role of that zvol or dataset or what service uses it (i.e., the system dataset, a share, virtual machine, or application).

Add Zvol displays after you select a root, non-root parent, or child dataset. It does not display if you select an existing zvol.
Click on any root or non-root parent dataset to expand the tree table. Click on any zvol to select it and display the widgets for that zvol.

Zvol Widgets

Each zvol has a set of information cards (widgets) that display in the Details for zvolname area of the screen and provide information grouped by functional areas. Add Zvol opens the Add Zvol screen. Dataset widgets are:

Zvol Details Widget

The Zvol Details widget lists information on volume type, and the sync, compression level, case sensitivity, Atime, and ZFS deduplication settings. Path displays the full path for the selected zvol.

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Edit opens the Edit Zvol screen for the selected zvol.

Delete opens the Delete zvol dialog.

Delete Zvol

The Delete button on the Zvol Details widget opens a window that includes information about other options or services that use the zvol. For example, a parent to other datasets and the services the child datasets of a parent dataset uses. Non-root parent and child datasets include the Delete button.

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The Delete window for a parent dataset (non-root) includes information about snapshots, shares, or other services such as Kubernetes or VMs that use the dataset. If it is a parent to other datasets, the window includes the services a child dataset of this parent dataset uses.

If a zvol uses services, the window displays them.


If a zvol is not used by a service, it does not display a service.

The window includes a field where you type the path for the zvol, and a Confirm option you must select to activate the Delete Dataset button.

Zvol Space Management Widget

The Zvol Space Management widget displays space allocation (reserved, used, available) for the zvol.

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The widget displays after unlocking encrypted zvols. The widget donut graph provides at-a-glance information and numeric values for the space allocated and used in the selected zvol. This includes data written and space allocated to child datasets of this dataset. It provides access to quota configuration options for the parent dataset and the child dataset of the parent, and for users and groups with access to the dataset.


Edit opens the Capacity Settings screen where you can set quotas for the zvol.

The widget displays quotas set for users or groups.

ZFS Encryption Widget

The ZFS Encryption widget displays for zvols configured with encryption. It includes the current state of the encryption, the encryption root, type, and algorithm used.

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The ZFS Encryption widget displays the Lock or Unlock options. If it uses key encryption instead passphrase The Export Key option displays if the zvol uses key encryption.


Edit opens the Edit Encryption Options for dataset window for the selected zvol.

For more details on encryption windows and functions see Encryption Settings.

Data Protection Widget

The Data Protection widget displays for all datasets or zvols. This widget provides information on the number of snapshots and other data protection-related scheduled tasks (replication, cloud sync, rsync, and snapshots) configured on the system.

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It provides access to the tasks found on the Data Protection screen through links.


Create Snapshot opens the Add Snapshot screen.

Manage Snapshots opens the Snapshots screen list view where you can manage snapshots.

Manage Snapshot Tasks opens the Data Protection > Periodic Snapshot Tasks screen list view where you can manage scheduled periodic snapshot tasks.

Manage Replication Tasks opens the Data Protection > Replications Tasks screen list view where you can manage scheduled replication tasks.

Manage Cloud Sync Tasks opens the Data Protection > Cloud Sync Tasks screen list view where you can manage scheduled cloud sync tasks.

Manage Rsync Tasks opens the Data Protection > Rsync Tasks screen list view where you can manage scheduled rsync tasks.

Add Zvol Screen

The Add Zvol screen has two screen options, Basic Options and Advanced Options. The Advanced Options screen include all the settings found on the Basic Options screen. The basic options display by default. Click Advanced Options to expand the settings that includes block size.

Basic Options Settings

The Basic Options settings on the Add Zvol screen are the same as those on the Advanced Options screen and the Edit Zvol screen.

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To open the Edit Zvol screen, click Edit on the Zvol Details widget. The Name setting cannot be changed after saving the zvol.


Zvol nameRequired setting. Enter a short name for the zvol. Using a zvol name longer than 63-characters can prevent accessing zvols as devices. For example, you cannot use a zvol with a 70-character file name or path as an iSCSI extent.
CommentsEnter any notes about this zvol.
Size for this zvolSpecify size and value. You can include units like t as in TiB, and G. You can increase the size of the zvol later, but you cannot reduce size. If the size is more than 80% of the available capacity, the creation fails with an out-of-space error unless you select Force size.
Force sizeSelect to enable the system to create a zvol where the size is over 80% capacity. By default, the system does not create a zvol of this size. While not recommended, enabling this option forces the creation of the zvol.


SyncSelect the data write synchronization option from the dropdown list. Inherit gets the sync settings from the parent dataset. Standard uses the sync settings requested by the client software. Always waits for data writes to complete. Disabled never waits for writes to complete.
Compression levelSelect the option from the dropdown list for the type of data compression to use or encoding information in less space than the original data occupies. Select the algorithm that balances disk performance with the amount space saved. See below for the options.
ZFS DeduplicationDo not change this setting unless instructed to do so by your iXsystems support engineer. Select to transparently reuse a single copy of duplicated data to save space. Deduplication can improve storage capacity, but it is RAM intensive. Compressing data is recommended before using deduplication. Deduplicating data is a one-way process. You cannot un-deduplicate deduplicated data!
SparseUsed to provide thin provisioning. Use with caution as writes fail when space is low on a pool.
Read-onlySelect the option to use to prevent modifying the zvol. Options are Inherit (off), On or Off.
SnapdevSelect the option that controls whether the volume snapshot devices under /dev/zvol/poolname are hidden or visible from the dropdown list. Options are Inherit (hidden), Visible and Hidden (default value).

Encryption options do not display unless you create the zvol from dataset using encryption.

Advanced Options Settings

The Advanced Options adds the Block Size setting to the Add Zvol screen.

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Block sizeSelect the size option from the dropdown list. The default is Inherit, other options include, 4KiB, 8KiB, 16KiB, 32KiB, 64KiB, 128KiB.

TrueNAS recommends a space-efficient block size for new zvols. This table shows the minimum recommended volume block size values by configuration (mirror or RAIDz type). Use this table to change the Block size value.

ConfigurationNumber of DrivesOptimal Block Size

Depending on their workload, zvols can require additional tuning for optimal performance. See the OpenZFS handbook workload tuning chapter for more information.

Data Compression Algorithms

Select the compression algorithm that best suits your needs from the Compression dropdown list of options.

LZ4 maximizes performance and dynamically identifies the best files to compress. LZ4 provides lightning-fast compression/decompression speeds and comes coupled with a high-speed decoder. This makes it one of the best Linux compression tools for enterprise customers.

ZSTD offers highly configurable compression speeds, with a very fast decoder.

Gzip is a standard UNIX compression tool widely used for Linux. It is compatible with every GNU software which makes it a good tool for remote engineers and seasoned Linux users. It offers the maximum compression with the greatest performance impact. The higher the compression level implemented the greater the impact on CPU usage levels. Use with caution especially at higher levels.

ZLE or Zero Length Encoding, leaves normal data alone but only compresses continuous runs of zeros.

LZJB compresses crash dumps and data in ZFS. LZJB is optimized for performance while providing decent compression. LZ4 compresses roughly 50% faster than LZJB when operating on compressible data, and is greater than three times faster for uncompressible data. LZJB was the original algorithm used by ZFS but it is now deprecated.

Encryption Options

Encryption options are the same on both the Basic Options and Advanced Options screens.

Encryption Options only display on the Add Zvol screen. To change encryption settings, use the Edit button on the ZFS Encryption widget.

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The default setting is Inherit. Clearing the checkbox displays the key encryption options. Clear the Inherit(non-encrypted) checkbox to display additional settings.


Selecting other options changes the settings displayed.

Inherit (non-encrypted)Select to clear the checkmark to display more encryption settings.
EncryptionSelect to clear the checkmark and remove the encryption settings from the Add Zvol screen. If the root dataset is not encrypted, leaving Inherit (non-encrypted) selected is the same as clearing the Encryption checkbox.

Edit Encryption Settings

Encryption TypeSelect the option for the type of encryption to secure the dataset from the dropdown list. Select Key to use key-based encryption and display the Generate Key option. Select Passphrase to enter a user-defined passphrase to secure the dataset. This displays two additional Passphrase fields to enter and confirm the passphrase and the pbkdf2iters field.
Generate keySelected by default to have the system randomly generate an encryption key for securing this dataset. Clearing the checkbox displays the Key field and requires you to enter an encryption key you define. Warning! The encryption key is the only means to decrypt the information stored in this dataset. Store encryption keys in a secure location! Creating a new key file invalidates any previously downloaded key file for this dataset. Delete any previous key file backups and back up the new key file.
KeyEnter or paste a string to use as the encryption key for this dataset.
AlgorithmDisplays for both key and passphrase encryption types. Select the mathematical instruction set that determines how plaintext converts into ciphertext from the dropdown list of options. See Advanced Encryption Standard (AES) for more details.
Confirm Passphrase
Enter the alpha-numeric string or phrase you want to use to secure the dataset.
pbkdf2itersEnter the number of password-based key deviation function 2 (PBKDF2) iterations to use for reducing vulnerability to brute-force attacks. Entering a number larger than 100000 is required. See PBKDF2 for more details.

See the list of Related Encryption Articles at the bottom of this article for more on encryption.