Raid?

[akif]

well, i do have heard about RAID but don't know its importance/advantage.

[saphalline]

RAID stands for redundant array of inexpensive disks or redundant array of independent disks - I'm not sure why there's two names for the same thing, but whatever. RAID is mainly used in servers because of its expensive nature and the special hardware that is needed. But first, what is RAID?

RAID is a way to take two or more physical hard drives and make them act as one logical hard drive. It's sort of the reverse of partitioning. When you partition a hard drive, you take one hard drive of say 80GB capacity, and you partition it into 2 sections of 40GB each for example. That means the computer sees two logical hard drives on one physical hard drive (because each partition can have its own drive letter). With RAID, let's say you configure two 40GB physical hard drives into one big partition of 80GB (one drive letter for both hard drives). You've just set up one kind of RAID array! :D Aren't you so proud of yourself? :p Ok, sorry, it's late.

There are many types of RAID, and they're given numbers to identify them. The version I gave above is called RAID 0 (zero) and is also called striping, where each hard drive holds equal-sized stripes of data, thus half of all data. So two or more drives make one big one (the number of drives used for RAID 0 must be an even number). Striping is good for speed, because both drives can be accessed in an alternating fashion so that when one drive is turning its spindle to fetch the next stripe, the other is already there. Throughput rates aren't quite doubled in this way, but the increase is often 40-70%! Very important for servers! The down side to RAID 0 is reliability. If one hard drive fails or gets corrupted, all data is lost! :eek: I mean, what do you do if you have half the shreds of a shredded document? You sure as heck won't be able to read it!

RAID 1 is called mirroring and takes two or more drives (again an even number of drives must be used) and copies them. So each drive contains the exact same data, and the total capacity is equal to just one drive. So two 40GB hard drives in RAID 1 still gives 40GB of capacity. This version doesn't speed up anything but it also doesn't slow anything down. The big advantage here is data integrity. So if one drive fails or gets corrupted, you haven't lost any data. Very important for sensitive data (like your bank info!).

The other versions of RAID are hybrids. RAID 0 + 1 is just called striping with mirroring. Pretty boring description, but it takes the best of RAID 0 and RAID 1, but requires hard drives to be used in multiples of 4. With this version, you can take four 40GB hard drives and make one 80GB hard drive. Two are striped, so you get the speed bonus, and the other two are copies of each striped drive, so you also get data integrity. Good hybrid, but extremely expensive! Of course, the integrity won't last if two drives with the same data fail, but if the two failing drives happen to have opposite data, then you're left with a RAID 0 array and two dead drives! :p

RAID 5 is a bit odd. It's called striping with parity and requires at least 3 hard drives (beyond that I don't how many are required for more drives). A piece of each drive is set aside for parity data, which is a summary of all the data on the other two drives. The rest of the drive is used for three-way striping. This version gives a decent speed boost, but also maintains a certain degree of data integrity in that a RAID 5 array can survive if one drive fails or gets corrupted. Because the other two drives can use their parity summary to fill in the blanks of missing data. A RAID 5 array can't survive the failure of two drives, tho.

Traditionally, RAID was used in servers because it requires a separate controller chip, and only SCSI RAID controllers were made. Since then, storage prices have plumeted and IDE RAID controllers have been made. You can now buy a couple of standard IDE hard drives and set-up your own home RAID array using either a PCI IDE RAID controller card, or use one of the many mobo's that have an IDE RAID controller chip built into them.

Most people who use IDE RAID often set-up a RAID 0 array for extra speed. Understandable, but considering that RAID 0's downfall is that data is twice as likely to get lost, I wouldn't recommend it. Most hard drives are already down to a one-year warranty. RAID 1, on the other hand, is getting a bit paranoid for the average user. I guess if I ever wanted a RAID array, I'd use 0 + 1 or 5, but that's just personal preference. :cool: