Multipath I/O (MPIO) is associated with high availability because a computer will be able to use a solution with redundant physical paths connected to a storage device. Thus, if one path fails, an application will continue to run because it can access the data across the other path.
The MPIO software provides the functionality needed for the computer to take advantage of the redundant storage paths. MPIO solutions can also load- balance data traffic across both paths to the storage device, virtually eliminating bandwidth bottlenecks to the computer. What allows MPIO to provide this functionality is the new native Microsoft Device Specific Module (Microsoft DSM). The Microsoft DSM is a driver that communicates with storage devices— iSCSI, Fibre Channel, or SAS— and it provides the chosen load- balancing policies. Windows Server 2022 supports the following load- balancing policies:
Failover In a failover configuration, there is no load balancing. There is a primary path that is established for all requests and subsequent standby paths. If the primary path fails, one of the standby paths will be used.
Failback This is similar to failover in that it has primary and standby paths. However, with failback you designate a preferred path that will handle all process requests until it fails, after which the standby path will become active until the primary reestablishes a connection and automatically regains control.
Round Robin In a round- robin configuration, all available paths will be active and will be used to distribute I/O in a balanced round- robin fashion.
Round Robin with a Subset of Paths In this configuration, a specific set of paths will be designated as a primary set and another as standby paths. All I/O will use the primary set of paths in a round- robin fashion until all of the sets fail. Only at this time will the standby paths become active.
Dynamic Least Queue Depth In a dynamic least queue depth configuration, I/O will route to the path with the least number of outstanding requests.
Weighted Path In a weighted path configuration, paths are assigned a numbered weight. I/O requests will use the path with the least weight— the higher the number, the lower the priority.
Exercise 11.6 demonstrates the process of installing the Microsoft MPIO feature for Windows Server 2022.
EXERCISE 11.6
Installing Microsoft MPIO
- Choose Server Manager by clicking the Server Manager icon on the Taskbar.
- Click number 2, Add Roles And Features.
- Choose role- based or feature- based installation and click Next.
- Choose your server and click Next.
- Click Next on the Roles screen.
- On the Select Features screen, choose the Multipath I/O check box (see Figure 11.6). Click Next.
7. On the Confirm Installation Selections page, verify that Multipath I/O is the feature that will be installed. Click Install.
8. After the installation completes, the Installation Results page appears stating that the server must be rebooted to finish the installation process.
9. Click Close.
10. Restart the system.
Typically, most storage arrays work with the Microsoft DSM. However, some hardware vendors require DSM software that is specific to their products. Third- party DSM software is installed through the MPIO utility as follows:
- Open Administrative Tools ➪ MPIO.
- Select the DSM Install tab.
- Add the path of the INF file and click Install.
Configuring iSCSI Target
Internet Small Computer System Interface (iSCSI) is an interconnect protocol used to establish and manage a connection between a computer (initiator) and a storage device (target). It does this by using a connection through TCP port 3260, which allows it to be used over a LAN, a WAN, or the Internet. Each initiator is identified by its iSCSI Qualified Name (iqn), and it is used to establish its connection to an iSCSI target. iSCSI was developed to allow block-l evel access to a storage device over a network. This
is different from using a network attached storage (NAS) device that connects through the use of Common Internet File System (CIFS) or Network File System (NFS).
Block- level access is important to many applications that require direct access to storage. Microsoft Exchange and Microsoft SQL are examples of applications that require direct access to storage.
By being able to leverage the existing network infrastructure, iSCSI was also developed as an alternative to Fibre Channel storage by alleviating the additional hardware costs associated with a Fibre Channel storage solution.
iSCSI also has another advantage over Fibre Channel in that it can provide security for
the storage devices. iSCSI can use Challenge Handshake Authentication Protocol (CHAP or MS- CHAP) for authentication and Internet Protocol Security (Ipsec) for encryption. Windows Server 2022 is able to connect an iSCSI storage device out of the box with no additional software needing to be installed. This is because the Microsoft iSCSI initiator is built into the operating system.
Windows Server 2022 supports two different ways to initiate an iSCSI session.
■ Through the native Microsoft iSCSI software initiator that resides on Windows Server 2022
■ Using a hardware iSCSI host bus adapter (HBA) that is installed in the computer
Both the Microsoft iSCSI software initiator and iSCSI HBA present an iSCSI qualified name that identifies the host initiator. When the Microsoft iSCSI software initiator is used, the CPU utilization may be as much as 30 percent higher than on a computer with a hardware iSCSI HBA. This is because all of the iSCSI process requests are handled within the operating system. Using a hardware iSCSI HBA, process requests can be offloaded to the adapter, thus freeing the CPU overhead associated with the Microsoft iSCSI software initiator. However, iSCSI HBAs can be expensive, whereas the Microsoft iSCSI software initiator is free.
It is worthwhile to install the Microsoft iSCSI software initiator and perform load testing to see how much overhead the computer will have prior to purchasing an iSCSI HBA or HBAs, depending on the redundancy level. Exercise 11.7 explains how to install and configure an iSCSI connection.
