What is RAID?

[youllbelost]

Can i get a detailed article on RAID. What is it? What does it need? What are its advantages?

I think i have RAID enabled desktop(if there is anything like that !?!)

How to enable the thing.
I think i have asked this question before. But i didnt get what it was..

wanna learn
YBL

 

[DeaconFrost]

This is a huge question to answer, but to get you started, it stands for Redundant Array of Individual (or Independent) Disks. There are different levels, denoted by a number, on how it uses the drives. My fave, and the only one with any real benefit in my opinion is RAID5. You need at least three disks, and you get the total capacity of the total number of disks minus one. The data is written across the drives, so if one drive fails, you don't lose anything. For example, if you had 4 500GB drives in a RAID5 array, you'd see a single, solid drive of 1.5 GB. If one drive failed, you could replace it, and it would rebuild...losing nothing, with zero downtime.

 

[youllbelost]

Oh its a whole different thing. I thought it is a connection through which you get godlike speed. But what i get is that it is primarily for Data Security. and it needs more than one drive for enabling RAID. ?
Am i right?

YBL

 

[DeaconFrost]

Yes, you need multiple drives to set up an array, but some can be configured with as little as two drives.

 

[pbcopter]

Check this out.
RAID - Wikipedia, the free encyclopedia

 

[pparks1]

This is a huge question to answer, but to get you started, it stands for Redundant Array of Individual (or Independent) Disks.

You are right, it is a huge question to answer. With most things, wikipedia is often a very good starting point for information on a new subject;
http://en.wikipedia.org/wiki/RAID

My fave, and the only one with any real benefit in my opinion is RAID5.

Perhaps that's the only on that you use, but they all offer benefits. For example, for pure speed RAID 0 is great. It stripes across 2 disks and doubles your speed. But there is 0 redundancy. RAID 1 is great, as it mirrors one drive on the second one. However, you do lose 50% of your total disk capacity and you get no speed gains..in fact you get a very tiny speed hit as 2 drives have to write the data. RAID 10 is very useful if you run something like a database. First it stripes the data across 2 drives (to give speed), but then mirrors them (to add redundancy). RAID 50's are cool as they stripe (with parity for redundancy), but then also stripe across 2 volumes to add back speed.

If one drive failed, you could replace it, and it would rebuild...losing nothing, with zero downtime.

Of course, with most home machines, you have to take downtime to actually remove the drive and replace it. With servers and such, they are usually hot swappable...so you don't have to turn it off at all.

With RAID 5, there is a performance penalty on writes, as it has to calculate parity bits on each and every write. So, with something like your OS drive and such that has high I/O...you don't want to use RAID 5 at all. RAID 5 is great for data drives...where you need data protection and you are doing much more infrequent writes.

 

[jfar]

Or this, plenty to read. High Performance SCSI & RAID: What is RAID ?

 

[DeaconFrost]

For example, for pure speed RAID 0 is great. It stripes across 2 disks and doubles your speed.

That's one of the largest myths ever debunked in the world of computing. Anandtech did the most definitive, and final report on the subject, and your real world performance is not what you'd expect. On top of that, seek times actually increase, slowing down certain operations. Only in rare, large file operations will you see any improvement, and even then, it is hardly double...it's more like 5-10%. That's why you don't see it anymore, unless it is with someone who's still buying into the hype and ignoring the facts. Anandtech's article is still online for any doubters. I participated in [H]ardOCP's large scale test back in the day with my two 36 GB Raptors. I used to think RAID0 was great, until I tested for myself. I ended up selling one of the drives for a larger storage drive...and lost nothing in the way of performance.

*Keep in mind my comments are only valid for mechanical drives...not SSDs. They are a whole new ballgame.

 

[pparks1]

For example, for pure speed RAID 0 is great. It stripes across 2 disks and doubles your speed.

That's one of the largest myths ever debunked in the world of computing.

Huh....not sure what you are talking about. A proper RAID 0 with fast hard drives and a solid RAID card when used for storage can provide fantastic results. I would not use it for running my operating system on.....as the small amounts of read/writes wouldn't benefit any. But for straight up file manipulation with large files and data sets, it makes a huge improvement.

But for somebody who frequently copies 50GB databases, and hundreds of GB's of virtual machines from 1 folder to a backup folder...a RAID 0 stripe makes a huge improvement.

And I'm talking about RAID 0 stripes usually with 2-4 drives, and mostly 15,000 RPM enterprise class SCSI/SAS drives. I'm not talking about home use with 2 commodity hard drives in a gaming rig thinking that I am l33t.

 

[DeaconFrost]

And I'm talking about RAID 0 stripes usually with 2-4 drives, and mostly 15,000 RPM enterprise class SCSI/SAS drives. I'm not talking about home use with 2 commodity hard drives in a gaming rig thinking that I am l33t.

Those drives are going to be fast anyway you use them. My gripe is with people who take two off-the-shelf consumer SATA drives, and run them in RAID0, suddenly talking about how great their performance is. That's the "myth" of RAID0 that was debunked.

My comments above shouldn't draw any surprises at this point in time. If you'd like, I'll dig up the article for you. it was pretty much the defacto word on desktop RAID0, but to your other point...it was only discussing consumer level drives.

Found a link:
http://www.anandtech.com/show/1371/11

 

[pparks1]

@Deacon. Yeah...we are talking about 2 different things entirely. RAID 0 with consumer class drives, on mobo based RAID setups, running an OS and games on it...will improve a bit...but it's nowhere near double. To me, not worth risk at all of data loss in the event that 1 of the drives fails.

But the straight up technology, when deployed in the right scenario...is solid.