We had to scrounge some SDRAM (synchronous dynamic RAM) because our Promise RAID (redundant array of independent disks) card didn't come with any. Thank heaven it passed Promise's memory test. |
Fault tolerance doesn't have to cut your storage space in half. Unfortunately, with the RAIDs (redundant array of independent disks) supported by many motherboards, such as RAIDs 1 and 0+1, that's exactly what happens. RAIDs 1 and 0+1 only leave you with 50% of your hard drives' capacity, thanks to their 1:1 mirroring of your data.
There's another option besides giving up data redundancy for RAID 0's 100% capacity. If you're willing to spend a couple hundred dollars on a controller card, you can build a fault-tolerant, relatively fast RAID that provides 66% or even 75% usable space. It's called RAID 5.
 Goal
Instead of mirroring data, RAID 5 stores parity (error-checking) information. If there's an error or bit corruption, the parity data should catch it, and the RAID controller should correct it. All data and ECC (Error-Correcting Code) are striped over three or more hard drives, which speeds up reads and writes.
Parity data takes up less space than mirrored data, so a RAID 5 can yield a total capacity of the sum of its drives, less one. As with other types of RAIDs, if you use differently sized drives, you'll lose access to the bigger drives' storage space above the smallest drive's capacity. To paraphrase controller vendor Promise, your RAID 5 will be the smallest drive's capacity times the total number of drives, minus one.
RAID 5's Achilles' heel is that it takes a lot of computational horsepower to maintain all that parity info, called XOR processing. If a motherboard supported RAID 5 without a dedicated processing unit, it would force the CPU to do much more work, slowing down the system. For desktop PCs, the best medicine is a RAID 5 controller card, such as the Promise FastTrak S150 SX4 we bought ($156; www.promise.com). Here's how we built a PC around that card for just more than $1,000, plus tax and shipping.
Background
Our Promise FastTrak S150 SX4 card packed four SATA (Serial Advanced Technology Attachment) ports, plus support for RAIDs 5, 0, 1, 0+1, and JBOD. It also came with four SATA data cables, adapters for four SATA power connectors, a printed quick start guide, a users manual on CD, and a driver diskette.
What the Promise card did not come with at $156 was the stick of RAM necessary to make the card work. And it wouldn't accept DDR (double-data-rate), either; it required a 168-pin stick of older SDRAM (synchronous dynamic RAM), which has gone up in price because no one makes a lot of it anymore. We heard a "yay" from the system administrator who wants to choose her own RAM, but a serious "boo" from the hapless consumer who didn't notice the fine print when he bought the card. We dug around in our derelict silicon locker and liberated a 128MB stick of PC133. Factor in $20 or more if you have to buy one of these. (Promise released a version with 64MB of RAM included, the FastTrak S150 SX4-M [price unavailable], after we ordered our parts.)
The Promise card works best with 66MHz PCI (Peripheral Component Interconnect) slots found on server motherboards, but it will also work with the 33MHz PCI bus on most desktop boards, too. You shouldn't notice too much of a limitation from the 133MBps (Megabytes per second) theoretical cap on a 33MHz slot, although the 266MBps of a 66MHz slot would probably allow faster throughput with current hard drives.
Although we used three Maxtor 6Y080M0 Serial ATA 80GB hard drives to keep costs down, you can add a fourth drive for even better performance. The Antec True430 power supply we bought is strong enough for a four-drive system. You can't really tell a good power supply before using it, but we will say that we've never encountered a high-quality PSU that didn't weigh much. Additional coil windings and internal heat dissipation sinks tend to help a decent PSU cope with surges and power spikes that would kill a lesser unit. Antec, Enermax, and Fortron all make reputable power supplies.
We've discussed our rationales for the other parts we chose for this PC in the other RAID articles in this "How ToInstall" area, so we'll skip them here. However, we should mention that our $64 copies of Windows XP Home that we bought online were just that: copies. They didn't have Microsoft's blue and green, barcoded, and hologrammed Certificate of Authenticity sticker. Worse, a fellow writer found that his copy's product key was already activated somewhere. We got our money back and spent $26 more on legitimate CDs.
The Build
One gripe we had about this build is that you'll need access to a working computer. You'll also need to create a bootable floppy disk by right-clicking it in Windows Explorer, selecting Format, and choosing Create An MS-DOS Startup Disk. Building our RAID 5 was a little different from assembling our other RAIDtypes, so refer to those additional "How To Install" articles for details and tips we didn't have room to include here.
First, we took the existing power supply out of our RaidMax case but didn't install the Antec just yet. We added a Compuman 80mm case fan in front of the 3.5-inch hard drive bays using two small bolts and motherboard standoffs as nuts, first flattening a raised section in our way with a stout bolt, nut, and washers. If you do this, make sure the fan blows into the case and 3.5-inch bays.
Next, we snapped the DFI motherboard's chromed I/O shield into the rear of the case. We then screwed standoffs into the case and mounted the mainboard on them. We installed the Athlon XP processor and its heatsink and connected the sink fan's power cable to the CPU FAN header on the motherboard. Once the heatsink was attached, we could carefully install the Antec power supply and connect its 20-pin and 4-pin power cables to the DFI board. If you install the PSU before this particular board, you'll have a terrible time trying to mount the heatsink.
Our AOpen CD-RW and Sony floppy drive went in next with four screws each. We popped out a 5.25-inch and a 3.5-inch plate in the case's plastic front panel to accommodate the drives. We added power cables and then ran data cables from the drives to the motherboard.
Speaking of the front panel, the DFI manual guided us to connect the panel's switches, LEDs (light-emitting diodes), and USB (Universal Serial Bus) ports to the proper headers on the motherboard. Next, we pressed our two sticks of DDR memory into slots DIMM1 and DIMM2. Your motherboard's manual will tell you which slots to put your RAM in; they're usually the two slots closest to the CPU. These days, it's better to buy RAM in matching pairs than singly, as many CPUs and motherboard chipsets can work faster with even numbers of DIMMs (dual in-line memory modules) instead of one or three. Our Athlon XP and nForce2 chipset are examples. |
Talk about a long expansion card. Our Promise FastTrak card almost touched our hard drives in this case.
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After we installed our Radeon 9200 SE video card, we connected it to our monitor via VGA cable. Two AC power cables later, we could start our PC. We immediately pressed DELETE to enter its BIOS (Basic Input/Output System) settings, where we set the S-ATA Or SCSI Card Boot field to SCSI Card (BIOSes often consider SATA drives as SCSI (Small Computer System Interface) devices for system configuration purposes). We also set the Init Display First field to Onboard/AGP; set the clock and date; and rearranged the boot devices to Floppy, CD-ROM, and SCSI, in that order. We saved our changes, exited, and shut down the PC.
Platter matters. It was now time to slide our four hard drives into the lower 3.5-inch bay, securing them with four screws apiece. Metal tabs in the case kept the drives about half an inch apart for cooling purposes, letting our Compuman fan do its job. Speaking of fans, we flipped the RaidMax case's side panel fan to blow inward, too. The power supply's fan would provide exhaust airflow, and rear case perforations would let the remaining air pressure, and heat, escape.
We put in the hard drives before the long Promise card so that we would have an easier time maneuvering them into place. In fact, the card is so long that when installed, it almost touches the rear of the hard drives in this case. We thought about mounting it in the bottom PCI slot, so as not to interfere with airflow through the case. However, this wouldn't have let the card or its RAM ventilate. We compromised and stuck the card into the next-to-bottom slot, first pushing out that slot's knockout plate in the case. One screw held the card's bracket down.
Next, we connected SATA data cables to the drives and to the Promise card's ports 1, 2, and 3. Note that because the card will manage our RAID 5, the hard drives will connect to it instead of the motherboard. We also powered the drives with 4-pin Molex leads from our Antec supply, ignoring its two SATA power hookups (use one type of power connection or the other). Promise said to connect our case's hard drive LED cable (HDD LED) to the FastTrak card instead of the motherboard, but we couldn't find any header for it on the card.
FastBuild. We started the PC, pressing CTRL-F when prompted to enter Promise's FastBuild utility. We selected 2 to Define Array and then pressed ENTER to select Array 1. You can use the Spacebar to change the RAID type, but we left it at RAID 5 for this article. Using the indicated navigation keys, we left Stripe Block at the default 64KB per Promise's recommendation, although a 16KB block size would have stored our data more efficiently. This setting determines the granularity of the data blocks the drives will store files in, which means you'll get more usable storage space with smaller blocks. Next, we changed FastInit to On. If you neglect to do this with a RAID 5 on this card, your array will be very slow—slower than a single hard drive.
We left Gigabyte Boundary enabled. This lets you replace a failed drive with another that has slightly more or less actual storage space, within 1GB, such as a Western Digital 80GB in an array built with Maxtor 80GBs. Next, we arrowed down to Assignment and used the Spacebar to change each drive from N to Y. Finally, we pressed CTRL-Y to save our new array, which FastBuild assumed would be the boot device. We pressed ESC and Y to exit and reboot the system.
Because some RAM isn't suitable for use on the FastTrak card, Promise wants you to run a utility to test the memory after you install it. However, we couldn't find the unnamed utility that was ostensibly on the CD, so we had to download it from www.promise.com (click Support and Download and then search the Utility category for the FastTrak S150 SX4 and Windows). Furthermore, the utility is meant to be run from a diskette after you boot with a separate startup disk, which we told you how to make at the beginning of The Build section. We feel that Promise could have easily included this RAM-testing software preinstalled on a diskette, as it did with the drivers. |
RAID 5
LEFT: A RAID 5 stripes data to most hard drives but writes parity (error-checking) information on the last drive in a shifting series. Splitting the parity data among the drives lets RAID 5 offer great speed and fault tolerance without sacrificing much capacity.
Capacity: A + B + C – one drive
RIGHT: A PC moves data to/from one unRAIDed hard drive at a time. Data isn't backed up, nor can it move as fast as in a RAID 5, but the computer can use the total capacity of all drives.
Capacity: A + B + C
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We unzipped the download using WinZip and then copied the three resulting files (Dos4gw.EXE, Memtest.EXE, and Readme.TXT) to a blank diskette. Next, we booted our nascent RAID 5 system into DOS with the startup diskette. When the A: prompt appeared, we swapped in the second diskette with the memory test on it. We typed memtest and pressed ENTER. Fortunately, our DIMM passed the test. If it hadn't, we could have located another stick of RAM relatively easily. You might not have such an easy time if you have to return a DIMM you've bought. It's probably worth it to simply buy the "M" variant of Promise's card, with memory included, in the first place.
We ejected the diskette, stuck the WinXP CD in the optical drive, and rebooted. Very soon, we had to press F6 to install third-party SCSI or RAID drivers. When Windows Setup asked us, we inserted Promise's driver diskette and followed the instructions. You may have to do this whenever you install WinXP on a SATA drive or RAID. Later in Windows Setup, we created a 10GB NTFS (NT file system) partition for WinXP, another 10GB drive letter for our apps, and a 134GB partition for our data. The roughly 160GB total available space reflected RAID 5's A+B+C-one drive capacity (80+80+80-80=160GB).
USB trouble. Twice during WinXP installation, we had to tell Setup to use the Promise drivers regardless of its out-of-date assertion that they weren't approved by Microsoft. Oddly, we lost support for our USB keyboard and mouse on the second occasion, despite USB keyboard support being enabled in the BIOS settings. At length, we had to press the PC's front reset button and let Windows Setup try that phase again. It didn't work until we used a different keyboard with a PS/2 connection and an adapter to connect the mouse to a PS/2 port. Even today, more motherboard BIOSes support PS/2 than USB before an OS loads, making USB keyboards and mice less attractive.
After Windows finished installing, we clicked Start, Control Panel, Switch To Classic View, Administrative Tools, Computer Management, and Disk Management. Here we right-clicked and Formatted the D: and E: partitions we'd created in Windows Setup, which automatically formats C: as it installs WinXP. Next, after installing DFI's motherboard drivers and updates, we updated the Promise card with new drivers from http://www.promise.com.
Testing
HD Tach showed maximum reads close to our RAID 0+1's and average reads about 20% better than RAID 1 or single drives. IOmeter also had a field day, reporting top scores in both tests. We think that the dedicated number-crunching hardware on the Promise card helped to route multiple data requests, which is what IOmeter tracks. However, PCMark wasn't impressed with our RAID to judge by its Hard Drive test score, which conspired with the weaker Radeon 9200 SE to bring the overall System score down.
In sum, RAID 5 falls between RAID 1 and RAID 0+1 in speed yet offers more usable capacity than either one. A fourth hard drive would have made our RAID 5 a little faster, Promise says, as would have a motherboard with 66MHz PCI slots.
Just for shucks and giggles, we tried a RAID 5 with four SATA drives to see whether Promise was right. We didn't have a fourth 80GB drive, so we used four Maxtor 6Y160M0 160GBs ($420 total, or $171 extra) with similar characteristics. Promise was dead on: 22% faster average reads, a 40% better Web server score, and a whopping 45% higher file server rating.
Final Remarks
If you're running a server, a four-drive RAID 5 is an outstanding choice. A three-drive system like the one we built isn't bad, but a fourth drive really uncorks performance. RAID 5 is also interesting in that you'll be able to use the full capacity of any hard drive you add to it.
by Marty Sems View the charts that accompany this article.
Time-saver
 When you're creating a RAID 5 using Promise's FastBuild Utility, always set FastInit to On. This synchronizes the drives for top performance. We didn't do this the first time we built this system, and it cut our RAID's speed in half.
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System Notes
RAID 5 offers more overall capacity than some other fault-tolerant RAIDs, so we got 160GB using three 80GB drives. Here are the other vital stats. AMD Athlon XP 2000+ 1.67GHz, 266MHz frontside bus, 128KB L2 cache, 462-pin (Socket A) 256MB (2x128MB) MemoryPRO DDR400 SDRAM, dual-channel 160GB usable storage (3x80GB Maxtor DiamondMax Plus 9 SATA hard drives, 7,200rpm, 8MB caches) RAID options 5, 0, 1, 0+1, JBOD 52X/32X/52X CD-RW 10/100MBps LAN S/PDIF output and input; 5.1-channel Realtek ALC650 audio Eight SATA ports FireWire 400MBps (IEEE 1394) |
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