iSCSI LUNs and Targets

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Last updated: Apr 13, 2023 by Sean HastertVersion comment

Overview

Sharing block devices via iSCSI is a common way to make network-attached storage available. An iSCSI LUN is a logical unit of storage. In SoftNAS®, the basic storage LUN is a volume that is accessed as a block device. The block device volumes have a mount point in the Linux /dev/zvol filesystem because they are disk block devices.

For example, a storage pool naspool1 with volume name lun01 would be named /dev/zvol/naspool1/lun01 as its mount point. These device references are links to Linux block devices used to access the volume's raw data blocks via iSCSI.

iSCSI targets are used by iSCSI initiators to establish a network connection. The target serves up the LUNs, which are collections of disk blocks accessed via the iSCSI protocol over the network. A target can offer one or more LUNs to the iSCSI clients, who initiate a connection with the iSCSI server.

For example, VMware vSphere or Windows connects to the iSCSI server and retrieves a list of available targets. Then, for each target, the list of its published LUNs are available for use.

Covered in this document:

Creating a Volume and Sharing as iSCSI Target

  • Create a new volume and select Block Device (iSCI LUN).
  • Select Share as iSCSI LUN.
  • Fill out other necessary information.
  • The block device volume is automatically added to the default iSCSI target.

The mountpoint for block device volumes is named LUN_lun1 (in the example below). Block device volume mount points always use the prefix LUN_ followed by the user-assigned volume name, to distinguish LUNs from regular filesystem volumes. Block devices are comprised of a sparsely-allocated file named lundata.dat. So for a pool name naspool and block device volume named lun1, the full mount point path is /naspool1/LUN_lun1/lundata.dat. These LUN names are automatically maintained by SoftNAS® and shown in the iSCSI Targets configuration panel, as well as the Volumes list.
The default is Thick Provision, which reserves space for the LUN at time of creation. Alternatively, choose Thin Provision, which will create a "sparse" LUN that only consumes space as it is actually used. 

More Information

For more information on creating a volume, refer to the Configuring Volumes section. 

Configuring and Sharing Storage using iSCSI

iSCSI LUN volumes can be shared by applying LUN Targets to the storage.

This can be done in one of two ways:

  • Directly at time of Volume creation, by switching to the LUN Targets tab after selecting Block Device (iSCSI LUN).

    OR

  • Via the iSCSI LUN Targets applet.

Applying The Target at Volume Creation Time

  • From Volumes and LUNS, click on Create.
  • Follow the standard instructions for creating a new Volume, and select Block Device (iSCSI LUN).
  • Switch to the LUN Targets tab that is now displayed.
  • Select the ellipsis

  • Select the appropriate LUN Target from the list.

    OR
     
  • Click the  icon to create a new target.

Applying The Target Using the Applet

  • From the Left Navigation Pane, select the iSCSI LUN Targets option under the Storage section. The iSCSI LUN Targets panel will be displayed.

  1. To create an empty iSCSI Target, click Create Target.

  2. Once the target is created, either double-click the empty target, or click Add LUN. The Add A LUN dialog box will be displayed.

  3. From the Volume Blockdevice drop-down, select the volume's block device.

  4. Click Add LUN to link the block device to the iSCSI Target as a LUN.


Screen Refresh

You may have to refresh the screen for the targets to present themselves.

  • The LUN is created and added to the target.  You may have to refresh the screen for the targets to present themselves.

Publish Block Devices

Publish any number of block device volumes via a single iSCSI target. However, you can use the Create Target button to add new targets as needed. 

Target Settings and Options

Each iSCSI target can be configured to restrict access to one or more iSCSI client IP addresses. It can also be configured to require authentication using a user name and password. 

  1. On the iSCSI LUN Targets panel, select the LUN target

  2. Click the Modify Settings option in the tool bar.  The Modify Target Settings dialog will be displayed. 

  3. By default, targets have unrestricted access from any IP address. To restrict which iSCSI initiators are allowed to connect to the target, enter one or more comma-separated IP addresses (or DNS names, if using DNS) in the Allowed Initiators text entry box. Use the CIDN notation to provide a range of network addresses; e.g., 172.16.150.0/24 restricts access to iSCSI initiators in the 172.16.150.* subnet only.

  4. In order to use login credentials while accessing the target, enter the user name in the User Name text entry box.

  5. Enter the password in the User Password text entry box.

  6. Once configurations are complete, click Save. 

Skip Credentials

If you wish to skip entering login credentials, leave the User Name and User Password fields blank.


Restart To Enforce

To enforce the changes, click Refresh on the iSCSI LUN Targets panel. 

Accessing the Target and LUN

To access the iSCSI target and its LUNs, make use of an SCSI initiator from another system on the network.

For more information, refer to the SoftNAS Reference Guide or the operating system reference guide associated with an iSCSI initiator.