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RAID Boxes

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BuriaL:
If you had 2x 1TB drives and "Mirror" them they are exactly the same. So when one breaks down the other is backup.

If you set them up as "Striped", you get faster disks, but if one breaks down then the whole arrays data is screwed.

The Wikipedia can tell you a bunch of stuff. And motherboards manuals usualy comes with a introduction on raid.

Arveene:
Tatsujin, I would suggest reading this. It's a fairly short explanation of what RAID is, the differences between RAID levels, and a bit of additional stuff. For your purposes, you'd probably only need to read about RAID 1, 5, and maybe 6.

The key advantages of using an external RAID for storage would be the following:
1. Data redundancy - RAID 1, 5, and 6 all allow for a hard drive failure without the loss of data.
2. You no longer have to store that data on your desktop computer. Most external raids can be hooked up to your network and you can stream media from it. (NAS)
3. Alternatively you can still have your copy on your computer and make a backup directly from your PC to the external unit. (DAS)

RAID right now usually isn't that hard to set up. It depends on your implementation and what you want to do with it. It should be a fairly simple task to set up a 4 disk external RAID and attach it to your network (NAS), or PC (DAS). A bit of a warning. A 4 disk external NAS would be fairly expensive to setup, and at that point you might be better off setting up a home RAID server instead. Network attached allows for streaming to any computer in your network, but might take a bit of tweaking to set up. Direct attached storage usually will require a PCI or PCI-X RAID card to be installed in your PC. So both implementations will require some work, but online sources for help and documentation is pretty good.

tl;dr of the link
RAID 1 = Mirrored. You take the data capacity of the smallest hard drive, multiply by the amount of hard drives and divide by 2 for your total capacity. (ex: 4x 1TB HDs = 1TB*4/2 = 2TB of mirrored storage.) RAID 1 allows for 2 disk failures in one mirrored set.
RAID 5 = Striping with parity data. You take the data capacity of the smallest drive, multiply by the amount of drives, and subtract 1. (ex. 4x 1TB HDs = 1TB*4-1TB = 3TB of storage with parity data.) RAID 5 allows for any one disk failure.
RAID 6 = Striping with dual parity data. You take the data capacity of the smallest drive, multiply by the amount of drives, and subtract 2. (ex. 4x 1TB HDs = 1TB*4-2TB = 2TB of storage with dual parity data.) RAID 6 allows for any 2 disk failures and also protects against another drive failure while the array rebuilds. If another disk goes down while rebuilding in RAID 5, you lose everything. The same can happen in RAID 1 if the "wrong" disk goes down while rebuilding. It also has an advantage over RAID 5 being able to protect data against an uncorrectable bit error rate.

Each of these RAID levels have a certain amount of redundancy, and different levels of performance. For just storage the performance hit won't be noticeable.

There's both benefits and disadvantages to each RAID level. I run with a 6x 750GB RAID 6 in my own desktop right now for a total of 2.72 TB of storage. Once I fill that up, I'll probably move my RAID card and drives to a home server instead and expand it.

Edit: I forgot to mention JBOD, that's covered in the FAQ briefly. I won't go over it though because quite frankly it's a waste of time and a waste of a storage controller.

geoffreak:
Keep in mind that redundancy is NOT a backup solution and should NEVER be used as such.

kureshii:
A good RAID discussion can take a long while; feel free to drop by #bakabt again if you prefer the discussion in real-time ;)

fohfoh:
You guys are mixing some things up. I don't know much about Raids...

But a 1 TB HDD will always be a 1 TB HDD. You can't really mux it into any thing else, and even if you can, it's pointless. The point of RAID is to make use of multiple HDDs at a hardware level. So basically, a mirror Raid (1,5,6 as mentioned above) is the amount of "mirroring" that occurs. That is, your information shows up, TWICE. Put it this way, you're basically just making a (for a lack of a better word, "backup") on your computer.
New 
However, the above is assuming mostly the same HDDs inside. Let's look this way.

If you have a raid set up in which you use 500GB x2 (for a total of 1 TB) for your system, then files are distributed across those two HDDs and used simultaneously. Two HDDs spinning at the same time can read files a lot faster than a single drive. It's moreso to eliminate a bottle neck. That to an extent is what people mean by "striping". Instead of a solid piece of paper, you distribute the files across 2+ HDDs in "cut up strips" of the original file. Then, when you access the files, you read them simultaneously on several HDDs for a faster reaction. (Reduction in bottleneck). However, i've only been talking about raid 0. In 0, no mirror occurs. So Raid 0 is only about performance.

Now, looking at the pictures above, I assume you want to have a mirror "backup". This looks into raid 1, 5, 6. Now, I can't really get into the differences, but how it works is this. You have 2 sides with approx equal HDD space. So, either you can do 1TB:1TB or 2x 500GB:1TB etc. (as long as you somehow can set it up hardware wise.) One side is used as the system use. (anime watching, storing, etc.) the other side is a total copy for stability purposes. (sort of like a backup of company files, and not a backup in the sense of "backing up" random files). "Now how it works is this. " remember the days before daemon tools? The "back up burn of your favourite game"? How it works is this. You have 2. One gets scratched to shit and unusable. The other "backup" is used. You replace that destroyed copy ASAP. Same case here except the data is always updated and not "set in stone" like a burned disc.

Now with my blah blah that might not be fully correct crap done, let's talk some other specifics.

Hardware vs Software raid.

Hardware raid has HDDs preset as used and the mirror sides. Just put in the right amount of HDD space on each side, and it will happily chug along with you without much push on the cpu.

Software raid just sits in the back and copies the required changes to the other side when necessary. Uses a little bit of CPU, but basically the same function.

More gibberish

Why the heck did I say 1TB: 1TB? Raids aren't really Raids without 3+ more HDDs. The main points of the Raid is #1, multiple HDDs seeking system, file etc info simult so you reduce HDD spin rate bottleneck. #2, goes into mirroring for a "sort of backup" so you don't lose data.

Performance Raid focuses on point 1
Storage/backup Raid focuses on point 2
 
Any wrong info here, please correct. I admit I'm a Raid n00b.

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