This week, we examine features and performance factors to consider when buying your first Network Attached Storage system, focusing on the solutions that would be of interest to a small- and medium-sized ISP businesses.

by Alex Goldman ISP-Planet Associate Editor [July 25, 2002]

Most first-time buyers look for reliability and performance when purchasing a Network Attached Storage ( NAS) appliance. But the key feature the device must possess is compatibility with existing network architecture. If the network that the device will be attached to runs Novell, then the NAS device must be Novell-compatible. If the network is running Linux, UNIX, or any flavor of Microsoft's Windows operating systems, then the NAS device must be compatible with the reigning network paradigm.

The NAS appliance must also work with your network's management system. This may require compatibility with a of a variety of network management protocols, including HP OpenView, Simple Network Management Protocol (SNMP), Telnet, or even the HyperText Transfer Protocol (HTTP).

Additionally, some systems may require Java, or compatibility with other proprietary languages. So you want to be sure that you know the requirements of your network management system before you go shopping for a NAS device. You will also need to account for Operating System (OS) file protocols, such as CIFS for Microsoft Windows systems, NFS for UNIX and Linux systems, AFP (AppleTalk) for Apple Macintosh systems, and NCP for Novell systems.

Factoring in fibre
Fibre Channel technology offers point-to-point, switched, and loop interfaces. Since Fiber Channel is designed to interoperate via Small Computer System Interface (SCSI), the Internet Protocol (IP), it can run over both copper and fiber (even though it sounds like it's fiber-only). If you've already built a storage network, odds are good that you used some type of Fibre Channel technology.

Currently, he most popular incarnation of the technology is Fibre Channel Arbitrated Loop (FC-AL). Although there are other protocols, most are either out of date or not yet fully standardized, and should not concern you.

Fibre Channel is expensive, but Storage Area Network (SAN) Fabric technology is even more expensive. If your ISP is a top-of-the-line operation and can afford servers that cost $100,000 or more, you may want to consider SAN Fabric technology to transfer data across network devices. SAN Fabrics use intelligent switches to allow a number of servers to access a large number of disks. In this segment of the storage market, Brocade is far and away the market leader.

One wild card technology is Gigabit Ethernet, which could theoretically be implemented by an enterprise of any size. If you plan to use the relatively new Gigabit Ethernet LAN standard, be prepared for some sticker shock. Gigabit Ethernet Network Interface Cards (NICs) are still quite expensive.

Raiding your budget
Another factor that will influence which NAS device you might buy for your ISP business is ease of deployment. You should examine the product yourself, speak with engineers and support staff, and try to talk with someone—ideally another ISP operator—that has already deployed the device, just to make sure make sure you're comfortable with it.

Once you've found a NAS system that's compatible with your network—these days, most systems should be interoperable, even if your network is Novell—expect to spend some time considering price versus performance.

All NAS systems that we know of use the Redundant Array of Independent Disks (RAID) disk drives of allocating data across several hard drives. The problem here is that there are many levels of RAID, numbered zero through ten, that allow for certain tradeoffs in performance factors. For example, RAID Level 0 improves speed of data transfer, but does not enhance data security.

Commonly used RAID levels today are 1, 3, 5 and 10. Advanced Computer & Network Corp., a data storage systems maker, provides a handy guide to determining which RAID level is right for your network.

As a rule of thumb, the higher the level of RAID, the more disk space and bandwidth will be used to increase fault tolerance and data integrity. Simpler NAS systems support the lower numbered RAID levels, while more complex and fully featured systems support a larger number of RAID options. There's no right answer—the choice is yours.

Other amenities
Whatever you do, you'll need a redundant power supply, which is just a fancy name for a backup power system. Hot-swappable hard drives are also a good idea, since changing drives without having to power down your entire network is always a good idea.

It's also a good idea to have a Level 2 Cache system in place. This is memory that resides outside of, but very close to, the Central Processing Unit (CPU). The Level 2 Cache allows a system to store frequently used data close to the CPU, improving performance. The actual size of the cache you buy depends more on your budget than your network because just having a cache system, even of the industry-minimum 128 K size, provides a real performance boost. Besides, anything larger is exponentially more expensive.

Marc Padovani, Dell PowerVault NAS product manager, says Dell's regular NAS product line comes with level 2 caches of up to 512 K, although top of the line products can have a 2 MB level 2 cache.

High-end NAS systems are sold with a second CPU option. In computer processing, each additional chip provides only an incremental increase in performance. Two 1 GHz chips, for example, might equal a single 1.5 GHz chips. A third 1 GHz chip might bring the system up to 1.7 GHz speeds. If you're paying less than $10,000 for your NAS system, you definitely don't need a second chip for the performance boost.

When evaluating the actual drives in the NAS system, look for the Advanced Technology Attachment (ATA) number. This determines the maximum bus speed of the disk. Disks are also rated by revolutions per minute. Currently, the industry standard speed is 7,500 rpm, with more expensive disks accelerating to 10,000 rpm, and the top of the line rocketing along at 15,000 rpm. For the average ISP operation, this would be overkill, but speedier disks still might fit into a larger ISP's network storage budget.

In summary, when buying your first NAS system, keep in mind that it must interact with the rest of your network. Make sure it is compatible with all of your network hardware and software, and you'll be fine. It's in the nature of NAS that at some point you'll want to upgrade your system. The life span of your system will depend on the rate of growth of your network, your budget, and the rate at which prices in the industry drop.

—End