RAID!!!

[Larry Hamilton]

This is a confusing concept. First, I purchased a new mb which allows RAID0 and 1 with SATA150 connections, it also allows 4 raid connections 0,1,0+1 and Jotb with ATA133 or less. While I am waiting for two SATA 150 hard drives (120g) to come in, I thought I should take the opportunity to learn from this group.

Suggestons or horror stories?

What's the confusing part? If you pick the best speed hd, you can only choose raid 0 (performance) or raid1 (reliability). You cannot choose both. If you pick the slower hd, you have 4 choices. Place you fingers on your lower lip and strum.....

[ceejay]

I'vr nefer used them myself, but if you can do regular backups (4mm DAT or something large like that) I'd go for "performance."

[JustRalph]

RAID offers many advantages over the use of single hard disks, but it is clearly not for everyone. The potential for increased capacity, performance and reliability are attractive, but they come with real costs. Nothing in life is free. In this section I take an overview look at RAID, to help explain its benefits, costs, tradeoffs and limitations. This should give you a better idea if RAID is for you, and help you to understand what RAID can do--and what it can't do.

As you read on, it's essential to keep in mind that with RAID, it's definitely the case that "the devil is in the details". Most common blanket statements made about RAID like "RAID improves availability" or "RAID is for companies that need fast database service" or "RAID level 5 is better than RAID level 0" are only true at best part of the time. In almost every case, it depends. Usually, what RAID is and what it does for you depends on what type you choose and how you implement and manage it. For example, for some applications RAID 5 is better than RAID 0; for others, RAID 0 is vastly superior to RAID 5! There are situations where a RAID design, hardware and software that would normally result in high reliability could result instead in disaster if they are not properly controlled.

Alright, let's take a look at the good stuff first. RAID really does offer a wealth of significant advantages that would be attractive to almost any serious PC user. (Unfortunately, there are still those pesky costs, tradeoffs and limitations to be dealt with... ) The degree that you realize the various benefits below does depend on the exact type of RAID that is set up and how you do it, but you are always going to get some combination of the following:

Higher Data Security: Through the use of redundancy, most RAID levels provide protection for the data stored on the array. This means that the data on the array can withstand even the complete failure of one hard disk (or sometimes more) without any data loss, and without requiring any data to be restored from backup. This security feature is a key benefit of RAID and probably the aspect that drives the creation of more RAID arrays than any other. All RAID levels provide some degree of data protection, depending on the exact implementation, except RAID level 0.
Fault Tolerance: RAID implementations that include redundancy provide a much more reliable overall storage subsystem than can be achieved by a single disk. This means there is a lower chance of the storage subsystem as a whole failing due to hardware failures. (At the same time though, the added hardware used in RAID means the chances of having a hardware problem of some sort with an individual component, even if it doesn't take down the storage subsystem, is increased; see this full discussion of RAID reliability for more.)
Improved Availability: Availability refers to access to data. Good RAID systems improve availability both by providing fault tolerance and by providing special features that allow for recovery from hardware faults without disruption. See the discussion of RAID reliability and also this discussion of advanced RAID features.
Increased, Integrated Capacity: By turning a number of smaller drives into a larger array, you add their capacity together (though a percentage of total capacity is lost to overhead or redundancy in most implementations). This facilitates applications that require large amounts of contiguous disk space, and also makes disk space management simpler. Let's suppose you need 300 GB of space for a large database. Unfortunately, no hard disk manufacturer makes a drive nearly that large. You could put five 72 GB drives into the system, but then you'd have to find some way to split the database into five pieces, and you'd be stuck with trying to remember what was were. Instead, you could set up a RAID 0 array containing those five 72 GB hard disks; this will appear to the operating system as a single, 360 GB hard disk! All RAID implementations provide this "combining" benefit, though the ones that include redundancy of course "waste" some of the space on that redundant information.
Improved Performance: Last, but certainly not least, RAID systems improve performance by allowing the controller to exploit the capabilities of multiple hard disks to get around performance-limiting mechanical issues that plague individual hard disks. Different RAID implementations improve performance in different ways and to different degrees, but all improve it in some way. See this full discussion of RAID performance issues for more.

If you want more, Go here----> http://www.storagereview.com/guide2000/ref/hdd/perf/raid/whyCosts.html

[Larry Hamilton]

thank you ralph, pearls!

[Larry Hamilton]

there is another concern. Mean Time Between Failures.

If you have 2 identical hd's running in series (Raid 0) the time is calculated by dividing by 2.

Raid 0--no negative effect, potentially infinite mean time. (with the ability to replace while running)

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performance story: My brother uses the Power Quest Drive Image to copy an image and replace boo-boos. Since the program runs in dos, and because he uses it frequently, he tells me that Raid 0 is approximately 500% times faster moving data to and from hard drives.