It is possible to build a SAN without spending a lot of money. Scott Lowe tells you how to do it for a small IT shop on a tight budget, or as a proof-of-concept project. It is not recommended for large data centers.
Recently, I wrote an iSCSI primer to kick off a series of articles on how to create an inexpensive iSCSI-based SAN. On such a system, you could conceivably add a ton of fairly inexpensive disk space, add software that turns a server into an iSCSI target, and create a relatively cheap SAN. With this block-based storage device, you can store information, such as Exchange databases, that work better using the block storage mechanism offered by SANs. In this article, I will cover hardware suggestions for both a pretty cheap solution and a slightly more expensive, but more stable solution. In future installments, I'll discuss (1) Linux targets: Installing and configuring software to turn a typical Linux system into an iSCSI workhorse and (2) Windows targets: The same task, but for Windows systems.
Note on terminology
Keep in mind that "iSCSI target" means the server which you plan to use for your centralized storage.
I'm not recommending that you run large data centers with mission-critical applications using these guidelines. This article is aimed at the smaller IT shop with a limited budget and at IT shops that need to quickly and cheaply demonstrate a proof-of-concept iSCSI project. I decided to cover this subject separately in order to demonstrate just how cheaply and easily you can jump on the iSCSI bandwagon.
Before I get into building a system, keep in mind that "cheap" doesn't need to equate to "junk". In fact, you can build a pretty decent system with loads of disk space for relatively little money. Or, you can go the slightly more expensive route and buy some prebuilt hardware. I'll go over both options in this article.
Regardless of which route you decide to go, there are a few factors to keep in mind:
- RAID is a must: Especially if you decide to use your cheap SAN in any kind of production capacity, you need to protect yourself from failure by—at a minimum, using something like RAID 5. Even for a proof-of-concept, use RAID to more fully demonstrate what you want to accomplish.
- With a SAN, the number of disks can have an effect on the overall performance of the system. Each disk (called a spindle in storage speak) can add performance to the system since it adds an additional piece of hardware across which data can be striped.
- As usual, RAM and processor speed also play a role in your building process.
- Since iSCSI is heavily dependent on the network in order to work its magic, don't use anything less than a gigabit Ethernet adapter for your storage needs. Better yet, bond multiple Ethernet adapters together for additional bandwidth and redundancy. For this hardware specification, I'll specify a single Ethernet adapter for the build-to-order system.
I'm not going to go into a blow-by-blow of the exact hardware you can use to build your iSCSI target server, except to say that you need a RAID card and as many disks as you can afford. You can probably spend less than $700 on a system with a decent motherboard, 2 GB RAM, a reasonably fast processor, a CD-ROM drive, a gigabit Ethernet adapter, and a case and power supply that can accommodate many disks.
As for RAID, consider a product such as Adaptec's Serial ATA RAID 2810SA, an 8-port Serial ATA controller that runs around $400. Combine that with about four Western Digital Caviar SE drives, each with 320-GB capacity and 8-MB cache and running at 7,200 RPM. These drives are about $175, for a total of $700.
Between the system, the RAID controller, and eight drives, you could have an iSCSI SAN with close to 1 TB of capacity for approximately $1,800, and you will leave yourself with some room to add up to four more disks on the same controller.
You can purchase a powerful ready-made system from a vendor, such as Dell, for surprisingly little money—if you're willing to buy refurbished gear. I've selected Dell for this example since you can easily get to their outlet store and get like-new equipment for a steal.
If you plan to roll out a production iSCSI target using the method in this article, you can pick up a refurbished Dell PowerEdge 2850 server with 2 GB RAM, dual gigabit Ethernet, and RAID for around $2,000. You can also buy a refurbished PowerVault 221S disk array with four 300-GB disks (providing just under a terabyte of storage after RAID 5 overhead is counted) for around $3,000. With just four disk slots occupied, that leaves you with ten more empty slots and a total potential capacity of just under 4 TB in a single array. Just make sure your system has an external RAID connector for your array. The total price: $5,000, with room for a ton of expansion. It's not the cheapest solution on the block, but it's certainly less expensive than a lot of options on the market right now.
The network equipment
You should probably pay attention to this area since iSCSI can be made or broken depending on what you choose. For this, make sure to get a gigabit Ethernet switch (or two if you want redundancy; in which case, you also need two gigabit Ethernet adapters in your server) that supports jumbo frames, a feature that moves Ethernet around the network using a much larger than normal frame size of 9,000 bytes vs. the normal 1,500 bytes. This larger frame size allows iSCSI traffic to move about the network using fewer frames, resulting in less overhead and better overall performance. You'll also need to make sure that the network cards in your server can support jumbo frames. If you pick a mainstream server system, this won't be a problem.
If you're planning to implement a small iSCSI network, you could use something like the 8-port SMC 8508T switch, which provides gigabit Ethernet speeds as well as jumbo frame support for a price of less than $100 each. Of course, this is for only 8 ports, so expansion is very limited, but $100 is a great price for a switch like this that supports jumbo frames.
For higher-end or larger applications, consider a 24- or 48-port gigabit Ethernet switch, such as the HP ProCurve 2824 (a 24-port switch) or the 2848 (a 48-port switch). Both offer jumbo frame support and are excellent units. The 2824 runs about $1,800 while the 2848 costs a little over $3,000. Bear in mind that, for redundancy, you'll need two switches. This part could easily cost more than the server you use for storage!
Odds and ends
In a powerhouse data center, would I recommend this approach for building a SAN? No way. But what about for a testing and development lab?Definitely. For a small network for which reliable backups are made every night, would I recommend these hardware solutions? Probably, but it would depend on the application.
I started with this part to demonstrate that the hardware side of iSCSI doesn't have to cost a fortune. If you want a "real" iSCSI array from a vendor like EqualLogic, go for it. It costs more, but you also get complete redundancy and an enterprise-level support agreement to go along with it, not to mention rock-solid stability. But, if you're on a tight budget, or want to develop a proof-of-concept project for your boss about the technology, just scare up some spare equipment, buy what you need, and then read the next parts in this series, in which I'll go over the process of turning your pile of hardware into a powerful storage array.