What is RAID?

Alright, I know I'm an idiot but I still don't understand the concept well. What exactly is it and what can it be used for the common user?

RAID: Redundant Array of Independent (or Inexpensive) Disks
- there is software raid and hardware raid, hardware raid is better.
- all raids basically take two or more hard drives and present them to the operating system as one drive.  you can configure this to enhance performance, reliability, or both (if you use a lot of drives)
this is what you can do with raid:
- raid can take two hds and interleave i/o operations on them, which increases performance since the os can do something with another drive while waiting for the first drive to finish.
- raid can automatically copy what you write on a drive to another drive, and rebuild the original drive in case of failure.  this requires 2 drives of like capacity and you only have totally capacity of 1 drive, but reliability is enhanced because it's an automatic backup.  read performace is not degraded but write performance is.
- with 4 or 5 drives you can combine these two functions.

someone should list the raid numbers.

>>1
It's basically a way to treat multiple hard drives as one. This can be used for speed (in the case of RAID 0), or, more commonly, for data safety. For instance, RAID 1 uses two hard drives and mirrors data between them. If one drive goes kaput, the other drive still has all the data on it. The more complex configurations use three or more hard drives.

You can also lessen the tradeoff by having RAIDs of RAIDs, which is often done in high-performance servers.

>>2 someone should list the raid numbers.
Yeah, someone should.
http://en.wikipedia.org/wiki/RAID

>>3 It's basically a way to treat multiple hard drives as one
That might over-simplifying it a little.
But then again there is JBOD, "just a bunch of disks".
And nesting of RAID levels, like 0+1 or 1+0.
Something like striped mirrors or mirrored stripes.
Oh and entire drives dedicated to parity or data regeneration.

hardware raid is not currently better. In fact, it may be better to use software raid because it's easier to interface with the controller.

There is no performance change.

Software raid is more taxing on your system though, which is why it's not favorable. The other problem is that you currently can't load your operating system on a software RAID solution.

For the lazy, I gave a rundown of the popular RAID setups.

RAID0 - Striping. Writes to 2 or more disks simultaniously to boost reading and writing speed. This method allows you to keep all of the space both of your HDs supply you with.

RAID1 - Mirroring. Every bit written to one disk, is automatically written to the other. You only keep the size of one of your disks and there are no changes to operating speed.  Mostly for backups.

RAID0+1 - Creates a stripe set, then mirrors the stripe set. This is kind of expensive to impliment as you need twice as many drives. I understand you can mirror only one drive but it doesn't make much sense to do so since there is equal chance for failure in other drives.

RAID5 - Striping with Parity. This is like RAID0+1 but it uses only one drive for fault tolerance. This means any 1 of your drives can fail and you will still retain all of your data. It's unlikely multiple drives will fail at the same time but if you lose 2 or more, all of your data is gone.

first.  be it nature or nurture, there are two kinds of people in the world.  RAID 0 people, and everyone else.  the two main problems with hard drives are seek time, and throughput.  RAID 0 with 2 drives comes close to doubling throughput.

this in most applications means nothing.  there are practically no benefits from using RAID 0.  the benefits you do get, are with large contiguous reads and writes which are rare.

now as for software and hardware.  software does well in benchmarks and bombs in the real world, hardware does bad in benchmarks, but much better then software raid in the real world.

welcome to the distinction between people who like RAID 0 and the people that know better.

>>1
its when the party van comes to your house

>>7
I had a RAID 0 solution for a couple of years. My motherboard came with onboard RAID support and I had two identical drives. It was neat for the novelty for a while but after I realized it's more trouble that its worth what with MTBF/2, needing a driver disk to install windows, the virtually zero noticable performance increase in my machine, etc. I dumped it.

>>9
Er, FYI the only reason I had it for a 'couple of years' is that I got my PC nice and cosy and really wanted to avoid formatting.

>>7
there is no difference between software and 'hardware' raid except the quality of the software that controls it.

A raid controller is software by definition. The only defining factor is where the software is. "Hardware" has a RAID controller that exists transparent to the software, making compatability easier but interfacing much more diffucult.

If you are using Windows, you want to use 'hardware' raid becuase Windows hates hates hates to live on a striped drive.

If you are using Linux, you want to use software raid because there is no performance loss and it's easier to interface with.

If you're using anything else, shame on you