SAN Switches

Low-Cost iSCSI

Just as the Fibre Channel IP protocols will strengthen your SAN investment, iSCSI will help you implement a less-expensive SAN setup over your IP network. ISCSI treats remote disks like they are directly attached to your machines, letting you centralize storage and storage management. Because iSCSI can be configured to behave like a SAN or NAS (network-attached storage), it is the most versatile option available. If you are just starting out with a SAN or planning a new SAN, iSCSI is worth investigating.

Some vendors offer iSCSI support that makes up for the maximum 1-Gbps speed of Ethernet with multiple Ethernet controllers, approaching or even surpassing the fastest available FC SAN speeds. So deploy iSCSI where it makes sense--in your SAN switch. You can hook iSCSI clients to your existing SAN hardware without modification. The right switch will permit iSCSI connections to your FC network, opening up potential uses for the SAN to a larger pool of systems. Users get data at the most reasonable price-performance ratio for their application, and you're a hero.

Application Support SAN management, replication and security applications appear to be headed for the SAN switch. In addition, though it isn't necessary, we recommend you purchase a SAN switch capable of hosting applications. If possible, find a storage vendor with a program that encourages third parties to develop applications for its SAN switch and tests these applications in its own labs.

Security applications are sure to be supported on the switch. Although applications have security built in, the aggregation of much of your organization's data on a single platform is likely to attract the attention of attackers once they are inside the network. This likelihood is increased with the growth of IP-based storage. Security on the client--either OS-based or application-based--will not protect your data from a rogue client with access to your switch, and security on the storage device will offer a potential single point of failure. By controlling access at the switch, you can prevent unauthorized users from accessing the data on your SAN, while using standard multiswitch failover configurations to avoid a single point of failure.

Counting the Ports

How many ports do you need? Get at least 50 percent more than you need today. The rate at which your data needs are growing and the increasing tendency to perform disk-to-disk backups on the SAN are going to have an impact on your setup. You'll have to add devices to your storage network, so make sure you purchase enough ports to handle them. Better to pay a little extra now than have to buy another switch in a year.

If you go with stackable switches, the number of ports, expressed as total number of ports in the fabric, must meet your needs for at least five years. The relatively high density of blade servers gives us even more connections to worry about, so watch that number as well. I'd rather buy a 16-port switch that can have up to 10 switches in the fabric than a 48-port switch that doesn't connect to anything else. Make certain there are no known incompatibilities between the switch vendor's products and your SAN-management software. Most vendors provide their own SAN-management tools, but these are generally designed only for their equipment. Be sure that any third-party tools you've bought work with your new switch.

Interoperability problems have dogged Fibre Channel since its inception. Some vendors claim that these questions have been addressed, but why take the chance? Look for third-party compatibility testing, such as that performed by the Storage Networking Industry Association (SNIA).

Speed Where You Need It

If you're running a small shop, speed may not seem to be a big concern, but make sure your choice of switch will carry you into the future. At a minimum, you'll need 2-Gbps support for older equipment, and 4- or even 8-Gbps support in the near future. Remember that there are two components to speed: that needed to support the ports to which SAN equipment and clients are connected and that for uplink ports. Uplink ports send a lot more data than client ports--because they aggregate for uplinking--so be sure your uplink ports support faster connections than the client ports do.

Availability and Redundancy Once your corporate data is placed on a common storage platform and applications are configured or designed to access that data from the SAN, you cannot afford to be without high availability on your SAN. Thankfully, vendors have taken steps to offer high-availability features in their switches. Even so, cover your bases by getting redundant power supplies and make sure you can configure redundant interswitch connections. We also recommend support for VSAN (virtual SAN) technology, to separate different traffic groups from each other easily.

What's Next

Before you buy, ask if firmware upgrades are free. Find out if there is an installation function in the management tools provided or if you must upgrade over FTP. Do you download upgrades or does the vendor ship them to you on CDs? Know your preferences and make certain you're comfortable with the tools the vendor provides.

The SAN switch market is on the verge of change. You must look for support of up-and-coming standards like iSCSI, FCIP and iFCP, plenty of connectivity for both clients and other switches, and the ability to run applications (developed by your vendor or by a third party and certified by your vendor) on the switch to ensure that you have the system needed for today and tomorrow. Determine your high-availability and redundancy requirements and be sure the switch you go with meets those requirements. All this investment of time and money will be moot if you miss even a single point of failure.

Don MacVittie is a technology editor at Network Computing. Previously he worked at WPS Resources as an application engineer. Write to him at [email protected]. 0