What Is MPIO?

In today's data-driven world, ensuring high availability and optimal storage performance is crucial. Without reliable storage, applications can become sluggish, transactions fail, and businesses grind to a halt.

Multipath Input/Output (MPIO) is a technology that significantly contributes to these goals by providing multiple physical paths between the storage devices and the host computer systems. Understanding MPIO is essential for IT professionals aiming to optimise their storage infrastructure and improve data reliability.

This article explores the workings, benefits, and implementation of MPIO in storage systems.

What Is MPIO?

Multipath Input/Output (MPIO) is a technique used in storage area networks (SANs) to provide multiple physical paths, such as Fibre Channel, iSCSI, or InfiniBand, from the host servers to the storage devices. The primary purpose of this is to enhance fault tolerance and performance by utilizing multiple paths for data transfer. If one path fails, MPIO automatically reroutes the I/O operations to another available path, ensuring continuous access to the storage resources.

Multipath I/O creates several redundant paths between the host and the storage device. These paths can be used simultaneously to balance the load or be on standby to take over if the active path fails. This redundancy ensures that the data transfer remains uninterrupted and efficient.

How Does MPIO Work?

MPIO works behind the scenes to optimise data transfer between storage devices and servers by utilizing two key mechanisms:

• Load balancing: Imagine all the data paths in a system as a multilane highway. MPIO distributes I/O requests (data traffic) across all available paths like cars using multiple lanes. By spreading the load, bottlenecks on any single path are avoided, leading to faster data transfer speeds. Likewise, all available paths are utilized effectively, maximising the overall network bandwidth available for storage traffic.
• Failover: Think of failover as a backup route. If a path malfunctions (like a lane closure on the highway), MPIO automatically reroutes data traffic to another operational path. This happens seamlessly, with minimal disruption to applications or users accessing the storage.

Benefits of MPIO

MPIO offers several advantages that significantly enhance storage system performance, reliability, and manageability. Some of these advantages include:

• Improved performance: By utilizing multiple paths for data transfer, MPIO can potentially double the bandwidth available compared to a single path setup. This results in faster data transfer speeds and improved overall storage system performance, which is particularly beneficial for applications that require high-speed data access, such as databases, virtual machines, and video editing software.
• Reliability and fault tolerance: With multiple paths available, MPIO significantly reduces the risk of a single point of failure. If one path malfunctions, the system seamlessly switches to an alternative path without interrupting service. This fail-safe design ensures continuous access to data, minimizing downtime and making MPIO ideal for mission-critical applications where even minor disruptions can be costly.
• Scalability and flexibility: MPIO provides a scalable storage solution. You can easily add new storage controllers or host bus adapters (HBAs) with additional paths, and the system automatically incorporates them for improved performance and redundancy. This flexibility makes it easier to expand storage capacity and enhance performance as your data storage needs grow.
• Simplified management: In some cases, MPIO can simplify storage management by providing a single interface to manage all paths between hosts and storage devices.
• Reduced cable complexity: MPIO can (sometimes) help reduce cable clutter by allowing the use of fewer physical cables to achieve redundancy compared to running separate cables for each path.

MPIO vs. Other Storage Technologies

MPIO is only one of the many techniques and technologies used to optimise the performance of storage systems. Typically, some of these technologies are used alongside MPIO to create a robust storage infrastructure.

MPIO vs. RAID

RAID (redundant array of independent disks) and MPIO aim to improve data reliability and performance, but they operate at different levels. RAID provides redundancy and performance improvement at the disk level. It achieves this by combining multiple physical disks into a single logical unit. RAID offers benefits like improved read performance through striping and redundancy through mirroring or parity schemes.

In contrast, MPIO operates at the path level. It ensures multiple redundant paths for data transfer between the host system and the storage device. While RAID focuses on data redundancy and speed within a storage array (composed of the disks), MPIO ensures connectivity redundancy and load balancing across the entire storage network, including the connections between the servers and the storage system.

MPIO vs. HBA

A host bus adapter (HBA) is a hardware component that provides the physical connection and data transfer capabilities between a host system (server) and a storage network. HBAs are essential for connecting servers to storage devices like disk arrays or SANs.

While HBAs provide the foundation for data transfer, MPIO builds upon them by managing multiple paths and ensuring failover and load balancing. In simpler terms, MPIO takes the raw connection provided by the HBA and adds intelligence to it, making the data transfer process more reliable and efficient. MPIO complements HBAs by adding redundancy and reliability to the data transfer paths.

Implementing MPIO

Depending on your operating system, you can implement MPIO as follows:

Windows Server

• Install MPIO feature

  • GUI method: Open Server Manager and navigate to Add Roles and Features. Proceed through the wizard, selecting Multipath I/O under Features and following the on-screen instructions.
  • PowerShell method: Use the following command in a PowerShell window with administrator privileges:

$ Install-WindowsFeature -Name Multipath-IO

• Enable MPIO for specific devices:

  • Open the "Computer Management" console and navigate to Storage > Disk Management.
  • Right-click on your storage device and select Properties.
  • Go to the "MPIO" tab and check the box to Enable multipath I/O.
  • You can further configure path selection policies and failover settings within this tab.

• Configure MPIO:

Use the mpclaim command to configure devices for multipath I/O.

$ mpclaim -r -i -a ""

You can check the Pure Storage FlashArray guides for a walk-through on setting up multipathing on a Windows server.

Linux

• Install Multipath tools:

For Debian/Ubuntu Linux distros, run the following command in a terminal with sudo privileges:

$ sudo apt-get install multipath-tools

For Red Hat/CentOS:

$ sudo yum install multipath-tools

• Configure Multipath:

Edit the /etc/multipath.conf file to define the multipath configuration. This step is optional and only recommended for advanced users or those needing specific configurations.

• Enable Multipathing service:

Finally, start and enable the multipathd service using the following commands in a terminal with sudo privileges:

$ sudo systemctl enable multipathd
 $ sudo systemctl start multipathd

Best Practices for MPIO Configuration

Optimizing your MPIO configuration plays a crucial role in maximising its benefits. Here are some best practices to keep in mind:

• Prioritize paths: You can configure path priority to ensure critical paths are used for data transfer. This is particularly important for storage devices carrying mission-critical applications.
• Load balancing algorithms: Choose the appropriate load-balancing algorithm based on your workload and storage array capabilities. Some common options are round-robin, least queue depth, and weighted paths.
• Monitor path health: Regularly monitor the health and performance of all available paths. Most operating systems provide tools to view path status and identify potential issues. Early detection of path problems can help prevent performance degradation or outages.
• Test failover: Don't wait for an actual failure. Periodically test the failover functionality to ensure MPIO seamlessly switches to a healthy path if a primary path fails. This proactive testing helps maintain high data availability and minimize downtime.
• Update MPIO drivers: Keep your MPIO drivers up to date. Driver updates often include bug fixes and performance improvements for MPIO functionality.
• Start simple: If you're new to MPIO, start with basic configuration options like enabling MPIO and using default settings. As you gain experience and understand your storage environment better, you can explore more advanced configuration options like path prioritization and custom load balancing algorithms.

Conclusion

MPIO is an important technology for enhancing the performance, reliability, and scalability of storage systems. By providing multiple paths for data transfer, MPIO ensures continuous access to data, even in the event of a path failure. Implementing MPIO according to best practices can significantly optimise your storage infrastructure. 

For advanced storage solutions, check out Pure Storage® ActiveCluster™ and Pure Protect™ //DRaaS for enhanced data availability and disaster recovery capabilities.