What you will learn in this tip: More small- and medium-sized businesses (SMBs) are discovering iSCSI is a good fit for their organizations. In this iSCSI primer, learn about what you need to get started with your first iSCSI storage system.
Some of iSCSI's popularity in SMBs has to do with server virtualization. And, right now, fault tolerance for virtualization hosts is a big factor that is pushing smaller shops into checking out iSCSI. In a virtual data center, it's imperative to prevent host servers from failing. If a host server were to fail, it would take all of the virtual machines (VMs) residing on it down, too. Since a single host server can contain a dozen or more VMs, a host server failure typically results in a major outage.
So what does this have to do with iSCSI storage systems? Well, to prevent the types of outages that I just described, many organizations cluster their virtualization hosts. That way, if a failure were to occur, the virtual machines can continue to run on an alternate host. Although there are a variety of host clustering technologies, host clustering typically requires the use of a shared storage pool that is accessible to all of the hosts within the cluster. The shared storage pool isn't connected to the cluster nodes through a disk controller. Instead, the cluster nodes communicate with the storage pool over the network through the use of the iSCSI protocol.
Hardware requirements for iSCSI storage systems
The only firm hardware requirement for using iSCSI is that there must be TCP/IP connectivity between the remote storage pool and the computer that needs to connect to it. Beyond that, it is widely considered to be a best practice to route iSCSI traffic over a dedicated, high-speed network connection so that iSCSI traffic won't be delayed by other network traffic, but this is not an absolute requirement. If you use a dedicated network connection (which I highly recommend), then you should use as high of a connection speed as possible. Using faster network connections between your server and your storage pool means lower latency, which is important, especially for I/O intensive applications.
Software requirements for iSCSI storage systems
To establish iSCSI connectivity, you are going to need a special type of software. The iSCSI storage array is usually a collection of disk resources that is physically attached to a Windows or a Linux server. This server runs iSCSI target software. Just as the shared storage pool requires specialized software, so does the server that connects to it. To establish a connection to an iSCSI target, a server must run an iSCSI initiator.
Establishing iSCSI connectivity
Once you have the iSCSI initiator and the iSCSI target software, the next step is to establish iSCSI connectivity. The exact procedure varies depending on the software that you are using. However, these are the five basic steps that are usually required:
1. Configure the iSCSI target to make disk resources available as iSCSI storage. On a Windows Storage Server, this means you must create a virtual hard drive and associate it with a specific iSCSI target (you can create multiple targets on a single storage server). When you run the iSCSI initiator, the software will assign the server an iSCSI Qualified Name (IQN).
2. Document this name and configure the iSCSI target to allow connectivity from that IQN.
3. Configure any firewalls between the server and the shared storage pool to allow iSCSI traffic to pass. iSCSI traffic usually flows over port 3260.
4. Provide the iSCSI initiator with the IP address of the Fully Qualified Domain Name (FQDN) of the iSCSI target.
5. Establish connectivity to the storage pool and map a drive letter.
Setting up an iSCSI storage system is nowhere near as complex a task as some people make it out to be. If you would like to learn more, Microsoft has an excellent article at Jose Barret's Blog.
About the author: Brien M. Posey, MCSE, has previously received Microsoft's MVP award for Exchange Server, Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. You can visit Brien's personal website at www.brienposey.com.