How do I configure iSCSI multipathing for fault tolerance and performance?

Configuring iSCSI multipathing is essential for fault tolerance and improved performance in your storage environment. Multipathing allows an iSCSI initiator to use multiple network paths to access storage targets, ensuring high availability and load balancing. Below is a step-by-step guide to configure iSCSI multipathing:

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Prerequisites

1. iSCSI Storage Array: Ensure your storage array supports multipathing.
2. Multiple Network Interfaces: At least two network interfaces on the host and storage.
3. Configured VLANs/Subnets: Ensure the storage and host are connected to separate VLANs/subnets for each path.
4. iSCSI Software: Install the iSCSI initiator software on the host.
5. Multipath Software: Install multipath software such as Device Mapper Multipath on Linux or MPIO on Windows.
6. Ensure Connectivity: Verify network connectivity between the host and storage targets for all paths.

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Steps for Linux Systems

1. Install Required Packages

Install the iSCSI initiator and multipath tools:
bash
sudo apt-get install open-iscsi multipath-tools
or
bash
sudo yum install iscsi-initiator-utils device-mapper-multipath

2. Configure iSCSI Initiator

Edit the iSCSI initiator configuration file (/etc/iscsi/initiatorname.iscsi) and set the initiator name:
bash
InitiatorName=iqn.2023-01.com.example:host01

3. Discover iSCSI Targets

Discover the iSCSI targets using the iscsiadm command:
bash
sudo iscsiadm -m discovery -t sendtargets -p <target_ip>
Repeat this command for each target IP.

4. Log In to Targets

Log in to the iSCSI targets:
bash
sudo iscsiadm -m node -T <target_name> -p <target_ip> --login
Repeat for each target path.

5. Enable Multipathing

Configure multipath:
– Edit /etc/multipath.conf:
text
defaults {
user_friendly_names yes
path_grouping_policy multibus
}
blacklist {
devnode "^sd[a-z]"
}
– Restart the multipath daemon:
bash
sudo systemctl restart multipathd

6. Verify Multipath Configuration

Check the multipath status:
bash
sudo multipath -ll
You should see multiple paths for the same storage device.

7. Configure Persistent Login

To ensure iSCSI sessions persist after reboot, enable the iSCSI service:
bash
sudo systemctl enable iscsid
sudo systemctl enable multipathd

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Steps for Windows Systems

1. Install iSCSI Initiator

• Open the iSCSI Initiator in the Control Panel (iscsicpl.exe).
• Configure the iSCSI initiator name.

2. Discover and Connect to Targets

• Go to the Discovery tab and add the IP addresses of the target storage.
• Go to the Targets tab, and connect to the discovered targets.

3. Install and Configure MPIO

• Install Multipath I/O (MPIO) feature:
• In Server Manager, go to Add Roles and Features → Enable MPIO.
• Configure MPIO:
• Open MPIO Properties from the Control Panel.
• Add support for iSCSI devices under the Discover Multi-Paths tab.
• Restart the server.

4. Enable Multipath for iSCSI Targets

• Reconnect the iSCSI targets.
• Verify multipathing:
• Open Disk Management.
• Check if the disks have multiple paths.

5. Configure Load Balancing

Configure the load-balancing policy for MPIO:
– Open MPIO Properties.
– Set the Load Balancing Policy to Round Robin or Least Queue Depth for performance.

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Best Practices

1. Separate Networks: Use dedicated storage networks/VLANs for iSCSI traffic.
2. Redundant Paths: Ensure redundant physical connections (NICs, switches) for fault tolerance.
3. Jumbo Frames: Enable jumbo frames (MTU 9000) for improved performance.
4. Network Bonding/Teaming: Consider NIC bonding or teaming for additional redundancy.
5. Monitor Paths: Regularly monitor the multipath configuration for path failures.

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Troubleshooting

1. Check Connectivity:
2. Use ping or telnet to test connectivity to the storage IPs.
3. Verify Multipath Status:
4. On Linux: multipath -ll
5. On Windows: Check MPIO properties and path count.
6. Logs:
7. Linux: /var/log/messages or /var/log/syslog.
8. Windows: Event Viewer → Storage Logs.

By following these steps, you’ll have a robust iSCSI multipathing setup with enhanced fault tolerance and performance.