8.1.3 - Configure An Iscsi Target

Let's dive into the intricacies of configuring an iSCSI target, a critical skill for any IT professional managing storage solutions in a modern network environment. iSCSI (Internet Small Computer Systems Interface) allows you to utilize existing IP networks to establish and manage connections between servers and storage devices, effectively turning network-attached storage (NAS) into block-level storage accessible by your servers.

Understanding iSCSI and Its Benefits

iSCSI operates by encapsulating SCSI commands within TCP/IP packets. This encapsulation allows data to be transferred across an IP network, making it appear to the operating system as if the storage device is directly attached. Think of it as creating a virtual SCSI cable over your existing network infrastructure.

The benefits of using iSCSI are numerous:

• Cost-Effectiveness: Leveraging existing network infrastructure eliminates the need for dedicated fiber channel hardware and cabling, significantly reducing costs.
• Simplified Management: iSCSI simplifies storage management by centralizing storage resources and allowing for easier provisioning and allocation.
• Scalability: iSCSI solutions are highly scalable, enabling you to easily expand storage capacity as needed.
• Disaster Recovery: iSCSI facilitates efficient data replication and disaster recovery strategies by allowing you to replicate data to remote locations over the network.
• Virtualization Integration: iSCSI seamlessly integrates with virtualization platforms like VMware and Hyper-V, providing storage for virtual machines.

Key iSCSI Concepts: Target, Initiator, and LUN

Before we delve into the configuration process, it's crucial to understand the key components involved in iSCSI communication:

• iSCSI Target: The iSCSI target is the storage server or appliance that provides the storage resources. It accepts iSCSI connections from initiators. In simpler terms, it's the server offering the storage.
• iSCSI Initiator: The iSCSI initiator is the client server that requests access to the storage resources offered by the target. It's essentially the server requesting the storage. Initiators can be hardware-based (using a dedicated iSCSI HBA - Host Bus Adapter) or software-based (using the operating system's built-in iSCSI initiator).
• LUN (Logical Unit Number): A LUN is a unique identifier assigned to a logical storage volume on the iSCSI target. It's like a partition on a physical disk, representing a discrete unit of storage that can be accessed by an initiator. A single iSCSI target can host multiple LUNs.

Step-by-Step Configuration of an iSCSI Target

The specific steps for configuring an iSCSI target will vary depending on the operating system or storage appliance you are using. However, the general principles remain the same. We'll cover the configuration process using common platforms like Linux (using targetcli) and Windows Server.

Configuring an iSCSI Target on Linux (using targetcli)

targetcli is a powerful command-line tool for managing iSCSI targets in Linux. It's commonly used in distributions like CentOS, RHEL, and Ubuntu.

1. Installation:

First, ensure that the targetcli package is installed. The package name might vary slightly depending on your distribution. Here are some common installation commands:

• CentOS/RHEL: sudo yum install targetcli
• Ubuntu/Debian: sudo apt-get install targetcli

2. Starting the Targetcli Shell:

Once installed, start the targetcli shell by running the following command:

sudo targetcli

This will open the targetcli prompt, which looks something like this:

targetcli shell version x.x.x
Copyright 2011-2017 Datera, Inc.
/>

3. Creating a Backstore:

A backstore defines the storage resource that will be exposed as an iSCSI LUN. You can use various backstore types, including:

• fileio: Uses a regular file as the storage backstore. This is useful for testing and development.
• block: Uses a block device (e.g., a physical disk or partition) as the storage backstore. This is the most common option for production environments.
• pscsi: Exposes existing SCSI devices as iSCSI targets.
• rdrd: (RADOS Block Device) Uses Ceph RBD as the storage backstore.

Let's create a fileio backstore for demonstration purposes. Replace /path/to/your/file.img with the actual path to your file. You'll also need to create the file first.

cd /backstores
create fileio my_file /path/to/your/file.img size=10GiB

This command creates a fileio backstore named my_file using the specified file and sets its size to 10 GB. Remember to replace /path/to/your/file.img with a valid path. You might need to create an empty file first using dd if=/dev/zero of=/path/to/your/file.img bs=1M count=10240 (which creates a 10GB file).

For a block device backstore, you would use:

cd /backstores
create block my_block /dev/sdb1

Replace /dev/sdb1 with the actual block device you want to use. Be extremely careful when using block devices, as incorrect configuration can lead to data loss.

4. Creating an iSCSI Target:

Next, you need to create an iSCSI target. Targets are identified by their IQN (iSCSI Qualified Name), which is a unique identifier. It's a best practice to use a reversed domain name format for the IQN.

cd /iscsi
create iqn.2023-10.com.example:storage.target1

This command creates an iSCSI target with the IQN iqn.2023-10.com.example:storage.target1. Replace com.example with your actual domain name or a suitable alternative if you don't own a domain.

5. Creating a LUN:

Now, you need to associate the backstore with the target by creating a LUN.

cd iqn.2023-10.com.example:storage.target1/tpg1/luns
create /backstores/fileio/my_file

This command creates a LUN that uses the my_file backstore.

6. Configuring Access Control (ACLs):

To control which initiators can access the target, you need to configure access control lists (ACLs). This involves specifying the IQNs of the allowed initiators.

cd /iscsi/iqn.2023-10.com.example:storage.target1/tpg1/acls
create iqn.2023-10.com.example:client.initiator1

This command allows the initiator with the IQN iqn.2023-10.com.example:client.initiator1 to connect to the target. Replace iqn.2023-10.com.example:client.initiator1 with the actual IQN of your initiator. You can find the IQN of your initiator using the iscsiadm -m discovery -t st -p <target_ip> command on the initiator host.

7. Configuring Network Portal:

You need to specify the network interface and port that the target will listen on for incoming iSCSI connections.

cd /iscsi/iqn.2023-10.com.example:storage.target1/tpg1/portals
create 0.0.0.0 3260

This command configures the target to listen on all network interfaces (0.0.0.0) on the standard iSCSI port 3260. If you want to restrict access to a specific interface, replace 0.0.0.0 with the IP address of that interface.

8. Enabling the Target:

Finally, enable the target to start accepting connections.

cd /iscsi/iqn.2023-10.com.example:storage.target1/tpg1
set attribute authentication=0
set attribute generate_node_acls=1
set attribute demo_mode_write_protect=0
enable

The authentication=0 disables CHAP authentication, which is fine for a test environment but strongly discouraged for production. The generate_node_acls=1 automatically creates ACL entries for newly discovered initiators. demo_mode_write_protect=0 allows write access.

9. Saving the Configuration:

To ensure that the configuration is persistent across reboots, save the configuration.

cd /
saveconfig

10. Exiting Targetcli:

Exit the targetcli shell.

exit

Example targetcli Script

Here's a consolidated script that performs all the steps outlined above:

#!/bin/bash

# Set variables
BACKSTORE_FILE="/path/to/your/file.img"
BACKSTORE_SIZE="10GiB"
TARGET_IQN="iqn.2023-10.com.example:storage.target1"
INITIATOR_IQN="iqn.2023-10.com.example:client.initiator1"

# Ensure the backstore file exists
if [ ! -f "$BACKSTORE_FILE" ]; then
  dd if=/dev/zero of="$BACKSTORE_FILE" bs=1M count=$(( $(echo "$BACKSTORE_SIZE" | sed 's/[^0-9]*//g') * 1024 ))
fi

# Start targetcli
targetcli <