Setting Up iSCSI Multipathing Manually on Linux

Multipathing (MPIO - Multipath I/O) is crucial for high availability and performance in iSCSI storage environments. It allows multiple network paths between a server (initiator) and a storage target, ensuring failover and load balancing. In this guide, we will configure iSCSI multipathing manually on Linux without Ansible.

1. Why Use Multipathing?

Multipathing is used in enterprise storage environments to achieve:

• Redundancy - If one network path fails, another takes over
• Load Balancing - Spreads I/O operations across multiple paths
• Higher Bandwidth - Uses multiple network interfaces for increased throughput
• Failover Support - Ensures continuous access to storage if a path fails

2. Requirements

2.1. Server-Side (iSCSI Target Requirements)

• The iSCSI target must support multiple network paths.
• Each LUN must be accessible via at least two separate IP addresses.
• Example target setup:

iSCSI Target:
IP1: 192.168.2.253 (eth1)
IP2: 192.168.3.253 (eth2)

2.2. Client-Side (iSCSI Initiator Requirements)

• Multiple network interfaces.
• The open-iscsi and multipath-tools packages installed.
• Two or more iSCSI sessions to the same LUN using different IPs.

3. Install Required Packages

On the iSCSI initiator (client):

sudo apt update
sudo apt install -y open-iscsi multipath-tools

Enable the services to start on boot:

sudo systemctl enable --now iscsid multipathd

4. Discover and Log In to iSCSI Targets

4.1. Discover Available Targets

Run the discovery command for each target IP:

sudo iscsiadm -m discovery -t st -p 192.168.2.253
sudo iscsiadm -m discovery -t st -p 192.168.3.253

Expected output:

192.168.2.253:3260,1 iqn.2025-03.com.example:storage
192.168.3.253:3260,1 iqn.2025-03.com.example:storage

4.2. Log In to Both Paths

sudo iscsiadm -m node -T iqn.2025-03.com.example:storage -p 192.168.2.253 --login
sudo iscsiadm -m node -T iqn.2025-03.com.example:storage -p 192.168.3.253 --login

Verify active iSCSI sessions:

sudo iscsiadm -m session

Expected output:

tcp: [1] 192.168.2.253:3260,1 iqn.2025-03.com.example:storage
tcp: [2] 192.168.3.253:3260,1 iqn.2025-03.com.example:storage

Set the login to persist across reboots:

sudo iscsiadm -m node -T iqn.2025-03.com.example:storage -p 192.168.2.253 --op=update --name=node.startup --value=automatic
sudo iscsiadm -m node -T iqn.2025-03.com.example:storage -p 192.168.3.253 --op=update --name=node.startup --value=automatic

5. Configure Multipathing

5.1. Enable Multipath

Edit /etc/multipath.conf:

sudo nano /etc/multipath.conf

Add the following configuration:

defaults {
    user_friendly_names yes
}

blacklist {
    devnode "^sd[a-z]"
}

multipaths {
    multipath {
        wwid "3600140547f55689de4b49c098d9b1a3c"
        alias mpatha
        path_grouping_policy "multibus"
        path_selector "round-robin 0"
        failback immediate
        rr_weight priorities
        no_path_retry 5
    }
}

To find the WWID for your LUNs, run:

sudo multipath -ll

5.2. Restart Multipath Service

sudo systemctl restart multipathd

Enable it at boot:

sudo systemctl enable multipathd

6. Verifying Multipathing Setup

6.1. Check Multipath Devices

sudo multipath -ll

Expected output:

mpatha (3600140547f55689de4b49c098d9b1a3c) dm-0 LIO-ORG  ,iscsi_target
size=20G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=50 status=active
| - 2:0:0:0 sdb 8:16 active ready running
|-+- policy='round-robin 0' prio=50 status=enabled
| - 2:0:1:0 sdc 8:32 active ready running

6.2. Monitor Multipathing

sudo systemctl status multipathd
sudo journalctl -u multipathd --no-pager --lines=50

7. Simulating a Path Failure

To test failover, manually disable one of the network interfaces:

sudo ip link set eth1 down

Check multipath status:

sudo multipath -ll

The failed path should be marked failed, but the system should remain operational using the second path.

Restore the path:

sudo ip link set eth1 up

8. Summary

In this guide we:

• Configured iSCSI multipathing manually
• Enabled automatic iSCSI login
• Set up multipath failover and load balancing
• Verified redundancy by simulating a path failure

This setup ensures high availability and performance in your iSCSI storage environment.