I had a conversation recently with Eric Herzog, vice president of marketing at Mylex, that centered on three new RAID cards the company will be announcing this month. But before we get to that conversation, let me relate some experiences.
I've been using RAID (redundant array of independent disks) configurations for five years or so. Usually, full mirroring isn't an option, either due to cost or space restraints, so I usually use RAID-5. For the most part, I've had very good experiences. RAID-5 does protect data, allowing a system to continue to operate when a single drive fails. I have had some less than perfect results, though.
On various systems, with different brand RAID controllers, I've occasionally had a disk drop off-line. Without RAID, the server would be in serious trouble and require immediate attention. With RAID-5, the server continues (usually with a fairly annoying BEEP-BEEP-BEEP drawing attention to the situation) until the server can be properly shut down (preferably after a full backup, just in case). In more than 90 percent of those occurrences, nothing is wrong with the drive. After a power down cycle, it recovers from whatever anomaly it experienced and resumes work, operating for many months or years. The RAID controller must be instructed to rebuild the array. That is not a problem unless the RAID controller support software in question is DOS-based and the server must be booted from a DOS disk and kept off-line until the rebuild is complete. Newer software will allow common operating systems to operate while the array is reconstructed. There's a trade-off here: risk versus downtime. You have no redundancy until the rebuild is complete, so if a second disk fails, you're hosed.
OK, back to Eric and Mylex.
Mylex is driving down the price of RAID controllers -- the new Mylex controllers will start at $499, list price. Those are single-channel, 160 MB/sec, wide controllers, capable of handling up to 15 drives. Two of the controllers are standard PCI form factor, designed for a normal, full-size server. One of those comes with 32 MB of cache, the other with 64 MB. Eric promised to get me one of the 32 MB cards to play with, and I'm looking forward to receiving it. And, of course, I'll let you know the results.
The third card is a new form factor being pushed by Intel. The form factor is supposed to allow more system boards to be installed in a smaller space in a rack. Think of an application service provider (ASP), a web hosting site or a co-location facility: hundreds of Intel-based systems and the closer together the boards can be stuffed, the less floor space you need. One ISP in Atlanta told me recently that there is no co-location space left anywhere in that city, so they're building a new facility to accommodate the growth. Having more computers in less space is another alternative.
With the price of disks continuing to drop, anyone who doesn't use some type of redundancy is very short sighted. If you can't afford full mirroring, then RAID-5 is a very attractive alternative. And now you can do it in hardware for not much more cost than a good SCSI adapter that doesn't do RAID.