Can someone explain how to enable RAID and what purpose it has?

[mr. nails]

i searched these forums and most info about RAID is over 1 year old and i know RAID has come up in the world since then. i also googled for info on RAID and that info is over 2 years old. can someone explain the different types of RAID (1-5 or whatever) and then explain the purposes behind them? i have never did RAID be4 and am considering doing so in my next build. granted that i find it necessary. do you still need a floppy drive for the installation of RAID? i will be using a MB with RAID onboard with SATA. pretty much all i know about RAID at this time is that it's enabled from within the BIOS and one of the RAID's config is 2 drives seen as 1 for performance or something and then 3 drives mirroring or what not. lol. that's about it. thorough explaination is GREATLY appreciated. thx!

[1Bullet]

RAID, or Redundant Array of Inexpensive Disks, is a technology that uses multiple hard drives to increase the speed of data transfer to and from hard disk storage, and also to provide instant data backup and fault tolerance for any information you might store on a hard drive.

The hard drives are joined in an array (a single logical drive, as far as the operating system is concerned) and all disks share the data written to them in some form. There are several different implementations, or 'levels' of RAID, ranging from RAID 0 to RAID 53.

The common factor that all RAID levels share is the use of a hardware or software RAID controller that intercepts data intended for storage on the logical hard drive. "Logical" being the hard drive space that the operating system sees as a drive letter, C:\ for example.

This data is then either duplicated by the controller for storage on multiple drives in the array at once ('mirroring'), or broken down into smaller chunks which are then divided between the available drives in the RAID array ('striping'). The terminology that is going to be important to understand from here on in is:

RAID array: A group of hard drives linked together as a single logical drive. Must be connected to one or more hardware RAID controllers, or be attached normally to a computer using a RAID capable operating system, such as Windows XP Professional.

Striping: A procedure in which data sent to a RAID array is broken down and portions of it written to each drive in the array. This can dramatically speed up hard drive access when the data is read back, since each drive can transfer part of the data simultaneously.

Mirroring: A procedure in which data sent to a RAID array is duplicated and written onto two or more drives at once.

By breaking down the data and sharing it amongst two or more drives, higher performance can be achieved, especially when reading data back, as each drive can transfer its portion of the required data simultaneously. Of course, striping data on two or more drives actually reduces reliability, since if a single drive in the array fails, all data is lost as each physical hard disk only contains a fragment of the data which is useless without the rest. To combat this problem, a third RAID technology is used called Parity.

RAID 1: Mirrored Disk Array A mirrored disk array is composed of a set of two physical hard drives, each of which contains a full copy of all data sent to the logical drive that represents the array. This has a couple of advantages; first of all, any data stored on a RAID 1 array is completely and automatically backed up, and in the event of the failure of one drive, the other can be substituted without a hitch. Secondly, data can be read from both drives simultaneously.

RAID 5:stripes both data and parity information across three or more drives. It is similar to RAID 4 except that it exchanges the dedicated parity drive for a distributed parity algorithm, writing data and parity blocks across all the drives in the array. This removes the "bottleneck" that the dedicated parity drive represents, improving write performance slightly and allowing somewhat better parallelism in a multiple-transaction environment, though the overhead necessary in dealing with the parity continues to bog down writes. Fault tolerance is maintained by ensuring that the parity information for any given block of data is placed on a drive separate from those used to store the data itself. The performance of a RAID 5 array can be "adjusted" by trying different stripe sizes until one is found that is well-matched to the application being used.

RAID 6 can be thought of as "RAID 5, but more". It stripes blocks of data and parity across an array of drives like RAID 5, except that it calculates two sets of parity information for each parcel of data. The goal of this duplication is solely to improve fault tolerance; RAID 6 can handle the failure of any two drives in the array while other single RAID levels can handle at most one fault. Performance-wise, RAID 6 is generally slightly worse than RAID 5 in terms of writes due to the added overhead of more parity calculations, but may be slightly faster in random reads due to spreading of data over one more disk. As with RAID levels 4 and 5, performance can be adjusted by experimenting with different stripe sizes.

RAID 7 isn't an open industry standard; it is really a trademarked marketing term of Storage Computer Corporation, used to describe their proprietary RAID design. (I debated giving it a page alongside the other RAID levels, but since it is used in the market, it deserves to be explained; that said, information about it appears to be limited.) RAID 7 is based on concepts used in RAID levels 3 and 4, but greatly enhanced to address some of the limitations of those levels. Of particular note is the inclusion of a great deal of cache arranged into multiple levels, and a specialized real-time processor for managing the array asynchronously. This hardware support--especially the cache--allow the array to handle many simultaneous operations, greatly improving performance of all sorts while maintaining fault tolerance. In particular, RAID 7 offers much improved random read and write performance over RAID 3 or RAID 4 because the dependence on the dedicated parity disk is greatly reduced through the added hardware. The increased performance of RAID 7 of course comes at a cost. This is an expensive solution, made and supported by only one company.

Redundancy Technique: Mirroring vs. Parity

The technique used to provide redundancy in a RAID array is a primary differentiator between levels. Redundancy is provided in most RAID levels through the use of mirroring or parity (which is implemented with striping):

Mirroring: Single RAID level 1, and multiple RAID levels 0+1 and 1+0 ("RAID 10"), employ mirroring for redundancy. One variant of RAID 1 includes mirroring of the hard disk controller as well as the disk, called duplexing.
Striping with Parity: Single RAID levels 2 through 7, and multiple RAID levels 0+3 (aka "53"), 3+0, 0+5 and 5+0, use parity with striping for data redundancy.
Neither Mirroring nor Parity: RAID level 0 is striping without parity; it provides no redundancy
Both Mirroring and Striping with Parity: Multiple RAID levels 1+5 and 5+1 have the "best of both worlds", both forms of redundancy protection.
The exact way that striping with parity is implemented depends on the particulars of the level as well. Some levels involve striping of individual bytes or sectors, while others use larger blocks; in the latter case, the size of the blocks is controlled by the stripe size of the array. RAID 2 uses a special form of striping with parity that is actually more like the ECC encoding used to protect data on various computer devices.

sorry if this is out of order cause I cant remember what it type before.

Most servers will be set up to use a form of raid with hot swap hard drives, that right they can remove a hard drive and if they using raid 6 they would not loose any data because the remaining hard drive by striping with parity would have the data on them from the failed hard drive. Loose 2 hard drives you will loose data.

You wouldn't you raid to back up everything only major important data, example the operating system, payables account receivables personal files all confidential files.Depends on the number of servers a company is running.

Everything else would be handled thru weekly to daily backups with one of three types of back ups.


If you were going to use raid it would be poinless unless you where using raid 6 with a minimum of 3 hard drives.

[1Bullet]

If you are still reading why would you want to use raid ? Because you can't afford to loose your Data.

How to set up on a pc. Buy a mother board that supports serial ata and set one hard drive to mirror the other one. Then if one fails then you have a back up of the orginal drive. You may(most likely) have to load a raid driver prior to installing windows. Windows is stupid when it comes to raid.

I do this for a living, and my PC has serial ata ,but I don't mirror my other drive.
I just back up important things onto DVD's or CD's.

If your still thinking of raid look into a hot site that way you will never loose your data.

[mr. nails]

lol, a good read, but most of what i read is over my head. is it possible for someone to break down what each RAID lvl does simplified? parity? redundancy? stripes? where's RAID 0?

RAID 1 = 2 HDD's mirroring each other (2x200gb = 200gb) so if u lose one hdd just slap in another and no problem? also, this is like hyperthreading? 2 HDD's acting like 1 HDD for faster performance?

thank you for this info as i'm trying to figure this out. lol, maybe easier to get hands on. which i would if i had a practice pc.

[1Bullet]

mirroring is 2 hard drives,(or more, or server to server ,one server mirrors another) one is active and one is mirroring. you loose the first harddrive and the second is switch to be active.the faulty hard drive is replaced and the mirrors the active hard drive.

stripping is for example 3 harddrives (you must have 3 or more),and lets say they are 300 Gb. A portion of each hard drive 100 GB is partitioned, all are active and receiving parts of the data on the 200 GB partition.The more hard drives the smaller the stripe (6 harddrives would only be 50 Gb)
So we have harddrive #1,#2 and #3.
#1 and #2(in there 100Mb partion) a have the data thats is on #3, #2 and #3 have the data that is on #1. So you have a total of 900 Gb of hard drive, but you are only able to use 600 mb for active storage. the other 300 Gb is only for back up.
If you lost #2 hard drive, replace it and the data on #1 and #3 would rebuild # 2. Loose #1 and #2 your out of luck unless you were mirroring with another server. And it would only be mirroring the 600 Gb.

parity refers to the checking whether data has been lost or written over when it's moved from one hard drive to another or when transmitted between computers.

here is a list of RAID
Level 0 -- Striped Disk Array without Fault Tolerance: Provides data striping (spreading out blocks of each file across multiple disk drives) but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost.
Level 1 -- Mirroring and Duplexing: Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks.
Level 2 -- Error-Correcting Coding: Not a typical implementation and rarely used, Level 2 stripes data at the bit level rather than the block level.
Level 3 -- Bit-Interleaved Parity: Provides byte-level striping with a dedicated parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely used.
Level 4 -- Dedicated Parity Drive: A commonly used implementation of RAID, Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails, the parity data is used to create a replacement disk. A disadvantage to Level 4 is that the parity disk can create write bottlenecks.
Level 5 -- Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.
Level 6 -- Independent Data Disks with Double Parity: Provides block-level striping with parity data distributed across all disks.
Level 0+1 – A Mirror of Stripes: Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. Used for both replicating and sharing data among disks.
Level 10 – A Stripe of Mirrors: Not one of the original RAID levels, multiple RAID 1 mirrors are created, and a RAID 0 stripe is created over these.
Level 7: A trademark of Storage Computer Corporation that adds caching to Levels 3 or 4.
RAID S: EMC Corporation's proprietary striped parity RAID system used in its Symmetrix storage systems.

How you determine what raid level to use is usually by how much money you have, again not common on PC's but on servers. We would not be talking about 300GB hard drives but 1 terabyte hard drives.

[1Bullet]

By the way lets keep Hyper Threading out of it . In my opinon it was a farse done by Intel. Anyone using it with Xp home that say it is great, is full of it, because it is not supported.

Just read your post again.

Raid is all about protecting the data (Fault Tolerence), not about performance. Your raid level will be based on the amount of money you have to protected the data from being lost.The more money you spend will improve the performance protecting the data.

If you are planiing on building a pc and you are thinking of using Serial ATA Hard drives you will not be intrested in doing any of the above. You will load your Raid driver from a floppy prior to your software install. with serial ata on your motherboard you will have the option now to having 4 IDE drives and 2 SATA drives.

[mildthrill]

Wow bullet, that pretty much blew my mind! Very Nice. Here's what I found in a recent article at Tom's Hardware (plus my own interpretations). It's only a few explained but I think any of the others would be irrelevant to a home build.

• RAID 0 (striping) divides data into chunks that are spread across two (or more) drives at the same time, providing up to double the transfer rate and the combined capacity of both drives. The major drawback is that if either hard drive fails, then you just lost everything. (Essentially, nothing is backed up, it just goes faster and you keep all your storage space, 2x200gb = 400gb! Beware if one drive dies).
• RAID 1 mirrors two (or more) drives so that if one fails, data can be recovered from the other. The major drawback here is that because both drives store the same data, the available capacity is half of the total capacity of the drives. (Like you were saying before, 2x200gb = 200gb, and there's no performance gain, it's all about security).
• RAID 0+1 allows four (or more) drives to be set up as a mirrored set of striped drives. If one striped set fails, data can be retrieved from the other, but total capacity is still limited to that of one striped set. (the speed of RAID 0 and security of RAID 1 together, but you need four hard drives!$! 4x200gb = 400gb)
• RAID 5 creates parity bits (which requires processing power and can slow down your computer!) for data recovery. Data and parity bits are distributed across all drives, increasing transfer rate, while sacrificing only the amount of space required to store the added parity bits (the capacity of one drive in the set)... Here's how my simpleton mind wraps itself around this one: The raid controller compresses your shit to fit on one hard drive as back up and all the other drives work together sorta like a RAID 0. So you'd need at least 3 drives, 3x200gb = 400gb. The bad part is when you're writing to the hard drives it eats up computer resources 'compressing' down stuff (see: creating parity bits) to go on the one backup drive. But while reading, it should be faster.

So that's pretty much the way I understand it... and bullet, feel free to to clarify if I've screwed it up.

As far as swapping out failed drives, I couldn't answer that since I've been lucky enough in my limited RAIDing experience to never have one fail. And yeah, the whole floppy routine during installation still applies. Not quite sure if that's changed any with vista.

For the record, I roll with a RAID 0 and manually backup music, pictures and the such on a third external drive.

[mildthrill]

lol! Looks like bullet beat me to the punch and published another RAID manual while I was trying to stumble through my comparatively meager thoughts on the subject. Oh well, maybe it'll be of some use, haha!

[mr. nails]

thx guys. a lot of my questions have been answered and i appreciate it. i just like to know stuff like this my my own info and it's good to know just in case u actually have to do it later down the road for some reason. u guys keep saying RAID is for protection and business' and stuff. why do so many of these ppl on this forum use RAID on their home systems then? same as stated above? lol, i really never saw a reason for myself to ever use RAID, but need to do it a couple of times so i can say i can do it and have. dito? any more valuable info out there plz share with us! thx.

[lynx]

Now for the KISS explanation of the most common types.

Raid 0 - striping.
Minimum requirement 2 drives.
Data is stored on each drive in turn, so large blocks of data can be recovered from multiple drives at the same time.
Advantage - performance.
Disadvantage - lose one drive and you lose ALL the data.

Raid 1 - mirroring.
Minimum requirement 2 drives, drives in pairs.
An exact copy of the data is stored on each of a pair of drives so if one drive fails a new copy can be built from the remaining drive.
Advantage - security.
Disadvantage - lose half the total drive capacity.

Raid 0+1 - striping and mirroring.
Minimum requirement 4 drives, drives in pairs.
As it suggests, the striped drives are mirrored.
Sometimes misnamed raid 10.
Advantage - performance and security.
Disadvantage - lose half the total drive capacity.

Raid 5 - striping and parity.
Minimum requirement 3 drives.
Data blocks are striped as in raid 0, with a parity block on the extra drive.
Works on the principle that A⊕B(⊕C⊕D...)=X, where A, B etc are the data and X is the parity. The ⊕ symbol means XOR. If you do not know any one of A, B (, C, D) or X you can work it out from the others because A=B(⊕C⊕D...)⊕X, B=A(⊕C⊕D...)⊕X, etc.
Calculation of the parity is done in HARDWARE (the XOR logic gate is one of the simplest gates there is) so there is no processor hit.
Each drive takes it in turn to have the parity block, so that if one drive fails the system doesn't have to do the recovery calculation for each read and the resultant performance hit until the drive can be replaced is minimal.
Advantage - performance and security.
Disadvantage - lose capacity of a single drive, potential performance loss on very large writes, but usually done in the background so not seen.


If anyone suggest that you should use anything other than the above in anything less than an extreme security environment, simply tell them to go boil their heads.

Explanation - Raid 10 - mirrored striping.
Minimum requirement 4 drives, drives in pairs, controllers in pairs.
Subtly different from raid 0+1, theoretically gives slightly better performance in some instances, but requires a controller for each side of the mirror therefore more expensive.