RAID, or Redundant Array of Independent (or Inexpensive) Disks, used to be the province of geeks and high-end IT departments. These days, however, it is finding a growing audience among small businesses as a means of increasing the reliability of critical systems, keeping a database online regardless of failures, preventing data loss, and accelerating information access.
"Disk failures are a reality," says Mike Karp, an analyst with Enterprise Management Associates. "Today's cheaper disks mean that small businesses can implement RAID inexpensively as a means of eliminating the consequences of disk failures."
While it may be comforting to look at the spec sheet for your server's hard drive and see that it is "guaranteed" to last anywhere from 300,000 hours to over one million hours, realize that this is nothing more than creative mathematics by disk manufacturers.
They have invented a reliability rating system expressed in Mean Time Between Failures (MTBF). If taken literally, MTBF would mean that disks would run for 114 years of constant operation (one million hours). However, MTBF is an approximation of first year failures. It doesn't say how long the drive will last, but rather what the odds are that it will break down within the first year of operation.
The higher the number, the less chance it will fail that year. Beyond the first two or three years, disk failure rates rise alarmingly.
"It's foolish to bank the company's future on one disk spinning inside a cheap server," says Chip Nickolett, a consultant with Comprehensive Solutions Incof Brookfield, Wisconsin, a company that has helped many small businesses implement RAID and other technologies. "While it might seem expensive and unnecessary to spend an extra few hundred dollars for a server with RAID capabilities, that's a small price to pay in comparison to losing your entire customer database."
In most areas of high tech, hardware prices are falling fast. This very much applies to RAID-based servers. According to research firm Gartner Inc., of Stamford, Conn., at the turn of the millennium, 100 percent of servers in the $10,000-plus price range had hardware RAID, whereas only 45 percent of the sub-$5000 server range had it.
These days, Dell sells the PowerEdge SC420 for less than $500 (without any software), which comes with two hard drives and very basic software RAID capabilities. Full hardware RAID is available in a server with six hard drives for less than $1200 (the PowerEdge 1800). Many businesses understandably might opt for the cheaper alternative. But if your data is valuable, a few dollars buys a lot of peace of mind.
RAID can be achieved either by hardware or via the operating system. Software RAID is cheaper, but ties up the operating system and impacts performance. Hardware RAID, on the other hand gives better performance and higher reliability in the case of a failure.
RAID, then, has two main purposes: to speed up data flow by simultaneously reading from or writing to more than one disk at a time, and to preserve data by replicating it among disks, so that if one goes down the others will still be working.
The basic RAID levels that small businesses need to be concerned with are:
- RAID Level 0 It increases performance by writing data to more than one drive. When you need to access it, you gather your data from each disk simultaneously so you can have much faster access. The downside is that if one drive fails, you lose your data.
- RAID Level 1 The exact same data is put on two or more disks. Read speeds are a little higher than a single disk, since more than one disk can be read at the same time. Write speeds are the same as a single disk, since all the data is written to each of the disks.
- RAID Level 5 This is a good choice to protect data and is the most widely used form of RAID. The read speed is improved, but the write speed is slightly slower than normal. If one drive fails, the system automatically reconstructs what was on the missing disk. By some computer "magic," it gives almost the same level of protection as RAID 1 without you having to double the amount of storage capacity to protect yourself.
- RAID Level 10 It is a combination of RAID-0 and RAID-1. It combines improved performance with protection against disk failures, but requires twice as many disks as RAID-1.
With RAID-5, you can get away with one drive failure. When a drive fails, the system continues without any data loss. But if a second drive goes down, you've lost the information. Fortunately, the chances of a second drive failing before the first one is repaired are fairly remote.
"Choose RAID-10 only if you need high performance," says Richard Scruggs, HP's product manager for server storage. "RAID-5, on the other hand, gives you decent performance as well as protection as against failures."
Many vendors now offer inexpensive RAID arrays aimed at small businesses. As well as Dell, HP and IBM, you also have companies such as Rasilient Systems that offer inexpensive servers with RAID 0, 1, 10 and 5.
"We keep our costs low by using standard motherboards and chips along with Linux-based software," says Sean Chang, president of Rasilient Systems. "We offer a flexible product with high performance at low cost."
For those businesses that store a lot of data and want to be extra safe, check out RAID specialist Infotrend. Its focus is to make traditional RAID configurations better while keeping prices low. Its EonStor F16F, for example, supports up to 124 hard drives.
If you investigated RAID a few years ago, the price tag probably scared you off. Those days, however, are long gone. RAID is now being built into most of the servers out there.
The Dell PowerEdge SC420 mentioned above, for example, was recently on special on Dell's Web site for $249. Note, though, that it only comes with software RAID for RAID 1. For a much faster and more robust RAID 5 or 10 system, the Dell PowerEdge 1800 could be bought for less than $1000. Online pricing changes very quickly, so that price may or may not be current. Check other vendors for similar deals.
"RAID has gone from a big-ticket item to a commodity piece," says Kenneth Hill, Technical Manager of Sun StorEdge at Sun Microsystems. "It has been reduced to a component of a larger system."
Drew Robb is a Los Angeles-based freelancer specializing in technology and engineering. Originally from Scotland, he graduated with a degree in geology from Glasgow's Strathclyde University. In recent years he has authored hundreds of articles as well as the book, Server Disk Management by CRC Press.
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