what is raid for exactly?

[diurnal]

I have raid on my motherboard but I have not installed it yet. What will raid exactly do for my system? Will it speed my hard drive performance? By the way I only have one hard drive hooked up to my system. I have heard that its only good for two hard drives.

[Paleo Pete]

Charles has a good section in the PC Guide on Redundant Arrays of Inexpensive Disks (http://www.pcguide.com/ref/hdd/perf/raid/index.htm) that might have some answers.

I don't pretend to know if it will give you better performance or not, you do need two or more hard drives, and lately it seems to be getting some attention with RAID controllers available to home users, or at least those of us who like to "roll our own" systems.

A few of the folks who help out here have somew experienc ewith RAID syatems, they might have some good comments about it too.



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[Randy_tx]

From all I have read.....it is a lot more "Hype" than reality and is only useful to "balance" the activity of numerous Hard Drives on one system(the claims of increased speed have not been shown in any review I've seen). The only REAL benefit I have seen so far(if you wanna call it that) is that you could hook up as many as 8 hard drives to one PC....Who's gonna do THAT???? http://www.PCGuide.com/ubb/biggrin.gif

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"As hard as a rock & dumb as a brick"...Windows CEMeNT

[spaceAlien]

Greets --

My $0.02 -- IDE RAID doesn't seem to be worth the bother. If you have an application that is important enough for RAID, then it is important enough for a SCSI system.

The only application I can think of is a RAID 0 (striping) swap partition for a Linux or BSD system.

My understanding is that IDE controllers can only talk to one device at a time, even if there are four devices on two channels.

If you have two controllers (or a controller that can talk to two channels at once) and two matched drives, then RAID 0 will give you better performance -- for disk I/O -- but if your not running a Web Server or Database Server -- why bother?

Same goes for RAID 1 (mirroring) -- if you're doing something where you need that kind of fault tolerance, then I think you need a industrial strength kind of system...

RAID 5 (stiping with one channel for checksum) requires at least three drives -- does you board have 3 IDE controllers?

Grins --


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[Paleo Pete]

According to what I've read in my technical publications, RAID was originally intended for large scale business applications where corporations have many machines on a large network, and important data that warrants serious protection.

RAID allows fast repair and minimum downtime, which is a major factor for some corporations. If a drive goes, the data is still there, shared on another drive, pop in another one and go, rather than completely losing the entire machine and having to rebuild it.

For home applications, it sounds a bit iffy from what I've seen posted in some of the forums. What Randy and Space Alien said has merit, SCSI or a back up IDE drive should be sufficient for most home users who don't have a network with important data to consider.

If you're doing CAD based engineering from home, or something similar, with major contracts on the line, maybe a RAID based server would be justified, but for typical home use I don't think it's really warranted.

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[ixl]

RAID is a tool, and like any tool, it is both very useful and incredibly useless, depending on how it is used. http://www.PCGuide.com/ubb/smile.gif
For a server in a multi-user client/server setup, it is IMO mandatory: it provides some measure of reliability, improved performance and high capacity.
The problem is that everyone seems to think they need RAID setups for their home PCs. In many cases the types of RAID being discussed are quite different with these machines, and the performance and reliability improvements are not really needed.

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Charles M. Kozierok
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[mjc]

One of things about the onboard RAID on many of the MOBOs is that it is also ATA100, which is what I want and it is cheaper than a new MOBO and controller card. And yes it isn't too hard to end up with more than 4 IDE devives on a system.

1. CD-ROM
2. CD-RW
3. DVD
4. ZIP/Jazz some type of removeable storage
5. One or more hard drives.

If you want keep things running at their best speeds putting a CD on the same channel as your brand new ATA100 HDD isn't going to work so the extra channels are nice.

I also haven't found many MOBOs that are offering onboard SCSI. IDE/RAID seems to be much more common and therefore less expensive.

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mjc
To ME or NOT to ME....

[Adrenaline]

I'm a little late on this discussion, so no one will pobably read it....

Anyway, I can't believe that there is so little support here for RAID. There are boards out there (i.e. Abit KT7A-RAID) that supports RAID, and does a good job of it.

Why use RAID?

Lets see...
1) Striping (at RAID level 0) WILL significantly increase access times. A simple setup of RAID0 with just two drives, one on each controller, will add a great deal of speed over a single IDE drive. Hands down!
2) I think I remembe someone saying something like <<if you want speed, go SCSI>> ummm... how about $$$? Dollar for dollar you can set up a nice set of IDE drives set at RAID0 and get great speeds. Opposed to going SCSI and going broke trying to match the storage capacity of just one of those IDE drives.

As far as I am concerned, spend the extra time and stipe a couple of IBM 75GXP drives, get great speed and storage capacity, all at a great price.

[David Stanford]

I agree. RAID can be extremely useful, or useless. I have 2 IBM 46G's on a FastTrak100 RAID for Audio/Video, and an IBM 30G on my onboard ATA100. The RAID drives run exactly twice in almost all benchmarks. That means the controller IS writing to both of them simultaneously. Really, the controller is just seeing twice the number of heads and platters.

Then again, alot of people point out that might be overkill even for native streaming DV ( digital video ). But as the drives fill up, that speed goes down, so I think it necessary.

For me, it was the best bang for the buck to get super large, fast storage. If you don't need that, shoot, the ATA100 is plenty fast.

By the way, RAID arrays are seen as SCSI by windows.

[spaceAlien]

Greets --

Originally posted by David Stanford:
If you don't need that, shoot, the ATA100 is plenty fast.


Exactly http://www.PCGuide.com/ubb/wink.gif My point is that for most home users in most situations, the advantages provided by raid are not utilized.

Having said that, technology will probably change tomorrow, and ide raid will become a "must have" http://www.PCGuide.com/ubb/rolleyes.gif

Grins --

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MOVE 'ZIG' FOR GREAT JUSTICE

[Dinosaur]

Previous posts have told a lot of the story. Here is some more information.

There is RAID-0 thru RAID-5 (Redundant Array of Inexpensive Discs). An alternative is called SLED (Single Large Expensive Disc).

RAID-0 makes two or more physical drives look like one huge drive. The drives must be identical. The RAID-0 concept is that the addressing of the huge virtual drive allows the first piece of a large record to be on one drive and the next piece on another drive. Alternation continues until the entire record is written. Data is sent to the drives concurrently. This addressing scheme is called "striping." The pieces can be as small as a 512-byte physical sector and as large as perhaps a 4096-byte cluster. The size of a piece is a parameter that is fixed at setup time. Size should be carefully chosen, depending on the characteristics of major applications.

In theory, 5 discs in a RAID-0 configuration will perform at 5 times the speed of the individual drives. In practice, latency considerations reduce this optimum speed. To get close to the optimimum speed, the drives must be synchronized (act as if on a common spindle) so latency positions are matched. Most users just do not need this kind of speed, and there are some disadvantages.

RAID-1 thru RAID-5 provide data redundancy. One of these modes allows two or more discs to be exact copies of eachother, so if there is an error on one drive, the data is available from one of the others, with the application software never knowing that there was a problem.

I think one of the modes provides both redundancy and the "striping addressing" of RAID-0 for extra speed. There is one mode that puts parity data on a different drive from the data.

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Gouverneur
Eschew Obfuscation!
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