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RAID questions

L

Limonov

Member
I've been looking into getting a motherboard with RAID support and have a few questions:

  1. Do I have to have two identical hard drives, or do they just have to be the same capacity?
  2. Which configuration offers the fastest performance?
  3. Where can I find more information on RAID?

Thanks!
 
1) Its best to have two identical Hard Drives. You definately want to have them same capacity otherwise your RAID array will only use the maximum capacity of the smaller HD on the larger HD. So a 40gb + a 60gb only would net you 80gb in RAID. You can get away with different drives but if you are using different drives, make sure they are at least the same specs in buffer size, RPMS, etc. Better with identical brands.

2) Well in terms of RAID mode, you'll find 3 different ones on consumer RAID mobos: RAID 0, RAID 1, and RAID 0+1. RAID 0 is what you are looking for. RAID 0 takes your two HDs and makes them into one so that data is written to the first HD then the second to and so on. So a 2mb file will be half on one drive and half on the other. This offers a boost in performance especially in large writes as your hard drives don't have to seek as much. Raid 1 is mirroring...ie your second HD acts as a backup in case the primary fails. RAID 0+1 is both so if you have 4 HDs you'll ahve a RAID 0 on the first 2 and the second 2 will mirror it. Server/Coporate RAID mobos/cards(very expensive) will also offer RAID 5. RAID 5 is like RAID 0 only with fault protection so that if one of the HDs fails in your RAID array, you won't loose the whole array. In terms of specific settings for RAID 0(ie size of each write before it moves to the second HD then back) refer to the articles in 3.

3) As for a guide...anandtech has an excellent one right here. Check out http://www.anandtech.com/storage/showdoc.html?i=1491 If goes into detail about RAID modes and benchmarks.
 
I personally think that this is the best site for RAID info, but I haven't seen the Anandtech one (sorry guys). It's quick and to the point. Let me make sure to mention one thing: if you go with Striping (a.k.a. RAID 0), you'd better be ready to lose all of your data. Think about it this way: if everything you write to your hard drive is 8kb, your packet size is 4kb, and one drive fails, you've half of every file gone. There ain't no coming back. I really like that IBM article because it goes through all of that. Many manufacturers offer RAID controllers, so take a look at them. By the way, the only RAID setup that I don't think that IBM site talks about is one called JBOD (seriously, it's on the specs of some mobos I've seen). It stands for "Just a Big Ol Disk". I think that if one of your drives goes down it won't take all of your data with it, but I'm not sure. I'd make sure that you check on it before you buy. Just remember this: don't go putting yourself in a position to get @$$-f@#$ed. RAID 0 is NOT a good option. My roommate's time saved with his slightly faster hard drives is nothing compared to the hundreds of hours that he spent collecting the 100+ GBs of MP3s that he lost last week. Hey, nobody thinks that their hard drive will crash until after it does. Go with either RAID 1 (better read performance and fault tolerance), 0+1 (better read and write performance and fault tolerance), or 5 (best read/write performance and fault tolerance).
 
In my experience, RAID 0 is exremely prone to errors. At least with my onboard HPT370 controller. RAID 0 totally trashed 2 brand new hard drives (uncorrectable partition problems) and had caused me to format and reinstall XP about 10 times in the span of 2 months. I ended up using the controller as a reguar IDE controller to support my many ide devices. The increase in speed of RAID 0 is not noticable and not worth the risk and hassle.
 
Originally posted by: LarryJoe
In my experience, RAID 0 is exremely prone to errors. At least with my onboard HPT370 controller. RAID 0 totally trashed 2 brand new hard drives (uncorrectable partition problems) and had caused me to format and reinstall XP about 10 times in the span of 2 months. I ended up using the controller as a reguar IDE controller to support my many ide devices. The increase in speed of RAID 0 is not noticable and not worth the risk and hassle.
Click to expand...


RAID 0 is not prone to errors. I have had three RAID 0 setups that have done very well and no problems. Neverwith Highpoint though, always with Promise. My latest is a 4-way RAID 0 with a FastTrack 100 TX4 and 4 60GB Seagate Barracuda ATA IV hard drives. Getting 75MB/s Write and 140MB/s Read performance, so don't tell me that the increase in speed isn't noticeable or worth it. Probably just a problem with your controller.

Speed increases probably won't be noticeable if all you do is email, word processing, web surfing, some gaming, etc. However when you do stuff like I do - Video editing, audio editing, photoshop, 3D stuff, etc. - you will definitely notice the increase.

 
Its really not correct to say that RAID 0 is more PRONE to errors. A 4 drive RAID 0 array is no more prone to problems than a 4 drive RAID 5. The difference is the effect of the problem on the array. A better statement would be that RAID 0 is more prone to DATA LOSS than any of the other levels. A single drive failure kills all the data with RAID 0 while a RAID 1,10,5 etc will tolerate a single drive failure with no data loss. A well implemented RAID 10 (plus other heirarchial levels like 50) can tolerate multiple drive failures before data is lost.

This does not mean RAID 0 is BAD... it just means that RAID 0 is best served in an appropriate application. It is quite fast with no write performance penalty which are very positive attributes. However... its not fault tolerant so its not for irreplacable data. Databases use RAID 0 a lot but they also keep transaction logs and backups (on RAID 1 or 5 usually) so the data can be recreated if a drive dies.
 
Thanks again to everyone! I guess I have to decide if I really need RAID or if it's just a new toy. I have a 40 gig Maxtor 7200 RPM drive now that's not even half full. I'm planning my next PC, mainly waiting for a 3 GHz chip. I like that new ABit MB with the USB 2.0, etc. ports (IT7?). One version has RAID, so I'm trying to decide if it's worth going for....
 
I don't use RAID myself personally, I don't do enough stuff where RAID would show benefits for me to use it. What I do use though are all those nice RAID slots on the IT7 that can also act as regular IDE channels. As a result, on my system, while I don't use RAID, every IDE device is on its own channel. But if I did more video editing and the like I probably would run RAID on my system.
 
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