HardDrive Horror

[ronin2040]

sigh, so much misinformation running around. The total resulting capacity will depend on what kind of raid is used. There are really only 3 options: Raid0, Raid1, and JBOD raid.

Raid 0 will increase speed, decrease reliability, and result in 80gb of useable space

Raid1 will increase reliability and read speed, but will result in a mere 40 GB of space

What you want is JBOD raid (technically, its not raid). It will do precisely what you're asking--the two disks will be treated as one. I'd do some research on JBOD, since i have no real experience with it. Chances are, though, you would have to buy a special controller card to set it up, regardless of which raid you use, and that could cost as much as a 120GB drive (guessing).

EDIT--whoops, didnt see mmX.memnoch's post

Edited January 3, 2006 by ronin2040

[nmX.Memnoch]

Chances are, though, you would have to buy a special controller card to set it up

Most of the cheapie cards that will do RAID0 and RAID1 will also do JBOD. JBOD is really only something you should use if you have, literally, just a bunch of disks laying around that you want to use but don't want to waste a bazillion drive letters just to use them.

Personally, I'd pick up another matching 80GB drive and stripe (RAID0) them for the speed...providing they're quality drives. If data integrity is your thing then mirror (RAID1) them.

RAID5 is something we're going to start seeing more in the enthusiast area because both NVIDIA and Intel are including support for it in their latest southbridge chipsets. RAID5 definitely is not the fastest though. What RAID5 does is offer a very good balance of speed and redundancy. It requires at least 3 drives to setup, but you can lose one of those drives and still not lose any data. Because of the algorithms for creating the parity stripe it uses a little more overhead as well (this should be negligible with a good hardware RAID controller).

[Vitalix]

So can't you have two drives with RAID 0 and not have the mirror?

You can, but that is called RAID-10 or RAID 1+0, which striping plus mirroring, but now you have 4 drives (two for the stripe and 2 for the mirror).

RAID5 requires 3 drives or more, but keep in mind not many RAID controllers support the XOR function for RAID5, usually those controllers are for file server usage. RAID controllers that support RAID5 will be more expensive.

The downside of a RAID0 array (two drives combined into one) is that is one blows, ALL of you data is gone on both drives. The upside is that RAID0 is lighning fast on the read/writes (especially if you have more than 2 drives).

The best bet is really RAID1 (mirror). The write speeds are slower, since the controller has to write to 2 places, but read speeds are as fast as a 2 drive RAID0 b/c the drives are identical and the controller can read from both drives at the same time (the data layout is same on both drives, so that controller can prefetch from the second drive while getting from the first).

[nmX.Memnoch]

The upside is that RAID0 is lighning fast on the read/writes (especially if you have more than 2 drives).

Just to touch on that a little more...

RAID0 speed increases don't scale with the number of drives you add. Two drives will give you anywhere from 25-50% speed increase (definitely not double), three drives will be a little faster, and four a little faster than three. It does eventually get to a point where adding more drives won't give you any benefit other than space.

RAID1 writes aren't that much slower than single drive write times. The data is usually written to both drives at the same time. The extra overhead is because the controller does a checksum of the files to make sure they're identical. This is a read operation though so it shouldn't be noticeable unless the controller has to make a correction to one of the files (not very common and could be a sign that things are starting to go bad).