Zvols
4 minute read.
Last Modified 2021-07-16 11:31 EDTA ZFS Volume (Zvol) is a dataset that represents a block device. These are needed when configuring an iSCSI Share.
To create a zvol in a pool, go to Storage > Pools then click and Add Zvol.
To quickly create a Zvol with the default options, enter a name for the Zvol, a size, and click SAVE.
| Setting | Value | Description |
|---|---|---|
| Zvol name | string | Enter a short name for the zvol. Using a zvol name longer than 63-characters can prevent accessing zvols as devices. For example, a zvol with a 70-character filename or path cannot be used as an iSCSI extent. This setting is mandatory. |
| Comments | string | Enter any notes about this zvol. |
| Size for this zvol | integer | Specify size and value. Units like t, TiB, and G can be used. The size of the zvol can be increased later, but cannot be reduced. If the size is more than 80% of the available capacity, the creation will fail with an “out of space” error unless Force size is also enabled. |
| Force size | checkbox | By default, the system will not create a zvol if that operation will bring the pool to over 80% capacity. While NOT recommended, enabling this option will force the creation of the zvol. |
| Sync | drop-down menu | Sets the data write synchronization. Inherit inherits the sync settings from the parent dataset, Standard uses the sync settings that have been requested by the client software, Always waits for data writes to complete, and Disabled never waits for writes to complete. |
| Compression level | drop-down menu | Compress data to save space. Refer to Compression for a description of the available algorithms. |
| ZFS Deduplication | drop-down menu | Do not change this setting unless instructed to do so by your iXsystems support engineer. |
| Sparse | checkbox | Used to provide thin provisioning. Use with caution as writes will fail when the pool is low on space. |
| Read-only | drop-down menu | Set to prevent the zvol from being modified. |
| Inherit (Encryption Options) | checkbox | Enabling causes the zvol to use the encryption properties of the root dataset. |
To see options for an existing zvol, click more_vert next to the desired zvol in Storage > Pools:
- Delete zvol removes the zvol from TrueNAS.
Deleting zvols can result in unrecoverable data loss! Be sure that any critical data is moved off the zvol or is otherwise obsolete.
Deleting a zvol also deletes all snapshots of that zvol. - Edit Zvol opens the zvol creation form for changing the previously saved settings. Similar to datasets, a zvol name cannot be changed.
- Create Snapshot takes a single current point in time image of the zvol and saves it to Storage > Snapshots. A snapshot Name is suggested and an extra option to make the snapshot Recursive is available.
When the selected zvol is cloned from an existing snapshot, Promote Dataset is available. When a clone is promoted, the original volume becomes a clone of the clone, making it possible to delete the volume that the clone was created from. Otherwise, a clone cannot be deleted while the original volume exists.
When the zvol is created with encryption enabled, additional Encryption Actions are shown.