RAID Explained...

[SMOKKINU]

I had a PM from a new member here, asking me about my RAID 0 setup with my two velociraptor HDD setup...i figured I would shaire my response with the rest of the forum, to explain what RAID 0 and RAID 1 is, and help you to decide what is right for you if you decide to attempt a RAID setup on your own computer.


Foregive my grammar, lack of punctuation, etc...but I believe i put it in leymans terms, so everybody can understand it

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RAID 0 basically makes 2 (Identical, they MUST be identical hard drives, model number and all) work in tandem... data, that is written, and read off of the drive, is written in 128kb "stripes", though you can change the stripe size to 64kb, or even 32kb... 64kb is probly the fastest, but i am running at 128kb stripe size...

anyway, say you have a 1gig file, in RAID0, that file is stored on both HDD, in tandem, written in 128kb chunks back and forth. thus making each HDD, only having to write 500mb, vs. the same HDD by itself, having to write the entire 1gb. so you cut the read/write time by essentially almost half...but not really... there is some latency involved, but RAID0 def beats out a single HDD.

If you got the money, go grab yourself two velociraptors, and run those in RAID0, its nice ;-)

Now, the other advantage to RAID0, is your essentially taking 2 hard drives, and creating one single large HDD. so windows see's my two 300gb raptors, as a 600gb HDD.

Then, there is RAID 1, raid 1, is a "Mirror" and is excellent for data security...if 1 hard drive fails, all of your data is still mirrored on the other, and you lose nothing. there is no performance increase, and you also do not gain any HDD space either...so if you take two 500gb HDD, and run them in RAID 1, your system still only has 500gb Hard drive space...it's just copying every single file, twice. It doesnt make it slower, it just makes it more secure if you are the type of person who values the files on their computer.

There is other RAID types, which essentially combine RAID 0 and RAID 1, but those setups require multiple Hard Drives of the identical model, and can get pretty pricey, unless you got the dough.

 

[SMOKKINU]

Oh, one thing to note, creating a RAID setup, of any type, you WILL need to start fresh, so backup any files/folders that are important before attempting such a setup, because a format, of both HDD is required to create a RAID Array.

 

[Ex_Brit]

Thanks. I may be old fashioned but I would prefer not to use RAID at all, but I see many PC vendors now don't give you any choice, it's either RAID 0 or 1...or nothing. Alienware's top of the line model ALX X58 for instance, which I have my eye on.

 

[H2SO4]

I had a PM from a new member here, asking me about my RAID 0 setup with my two velociraptor HDD setup...i figured I would shaire my response with the rest of the forum, to explain what RAID 0 and RAID 1 is, and help you to decide what is right for you if you decide to attempt a RAID setup on your own computer.


Foregive my grammar, lack of punctuation, etc...but I believe i put it in leymans terms, so everybody can understand it

-------------------------------------------------------------------------------

RAID 0 basically makes 2 (Identical, they MUST be identical hard drives, model number and all) work in tandem... data, that is written, and read off of the drive, is written in 128kb "stripes", though you can change the stripe size to 64kb, or even 32kb... 64kb is probly the fastest, but i am running at 128kb stripe size...

anyway, say you have a 1gig file, in RAID0, that file is stored on both HDD, in tandem, written in 128kb chunks back and forth. thus making each HDD, only having to write 500mb, vs. the same HDD by itself, having to write the entire 1gb. so you cut the read/write time by essentially almost half...but not really... there is some latency involved, but RAID0 def beats out a single HDD.

If you got the money, go grab yourself two velociraptors, and run those in RAID0, its nice ;-)

Now, the other advantage to RAID0, is your essentially taking 2 hard drives, and creating one single large HDD. so windows see's my two 300gb raptors, as a 600gb HDD.

Then, there is RAID 1, raid 1, is a "Mirror" and is excellent for data security...if 1 hard drive fails, all of your data is still mirrored on the other, and you lose nothing. there is no performance increase, and you also do not gain any HDD space either...so if you take two 500gb HDD, and run them in RAID 1, your system still only has 500gb Hard drive space...it's just copying every single file, twice. It doesnt make it slower, it just makes it more secure if you are the type of person who values the files on their computer.

There is other RAID types, which essentially combine RAID 0 and RAID 1, but those setups require multiple Hard Drives of the identical model, and can get pretty pricey, unless you got the dough.

Great post. Have rep

Depending on the implementation, disks don't have to be identical to function in a RAID 0 set.

Also, RAID 1 does confer a performance advantage. There are now two disks containing the same data, and one of them will have its head assembly closer to the target track and sector than the other one. Hence, seek time and rotational delay will be reduced somewhat.

 

[Dane]

Hi

I was told ones that you should be careful with "Raid 0" since a failur on one of the diskes destroys all the data on both diskes, and that failurs occur more frequently in "Raid 0" then they would in non Raid setups. Also if a normal disks fails you have a chance to recover the data with some software, this is not true for the raid setup... Or am I wrong?

Is there not a setup where you run two diskes like in "Raid 0" and have one extra disk for mirroring? Maybe Raid 2 or something...

Thanks for a great post by the why :D

 

[H2SO4]

I was told ones that you should be careful with "Raid 0" since a failur on one of the diskes destroys all the data on both diskes, and that failurs occur more frequently in "Raid 0" then they would in non Raid setups.

If the likelihood of a given disk model failing within the year is say 10%, then using two of them in a RAID 0 stripe set increases the failure risk to 19% ( 1 - [0.9]^2 ). Three of them in the stripe set, and the risk goes up to 27.1, and so on...

Strictly speaking, RAID 0 is not RAID at all. There is no Redundancy in that configuration.

Also if a normal disks fails you have a chance to recover the data with some software, this is not true for the raid setup... Or am I wrong?

In both cases, it depends on what exactly failed. If it's a complete failure at a hardware level, recovery software ain't gonna help either way. If the partition definition is somehow damaged, or the file system metadata, then assuming there's nothing wrong with the underlying hardware the data is potentially salvageable in both instances.

Is there not a setup where you run two diskes like in "Raid 0" and have one extra disk for mirroring? Maybe Raid 2 or something...

Sure, you can mirror two RAID 0 sets, and that goes by a variety of technically-incorrect names

Most larger hardware RAID arrays use RAID 5 as the basic building element. Again, it's a stripe set, except that for any given stripe across the disks one of the disks contains only parity information which can be used to reconstruct the original data should any single disk fail. The setup is truly "redundant" in the sense that it is fault tolerant. With massive hardware controllers it can come close to providing the speed of RAID 0 while still being as safe as RAID 1 - two disks must die (without replacement) before the data is completely lost.

 

[Thealien]

I am fairly new to all of this but my present computer came with two 500gb drives configured in a RAID O. They benchmark pretty fast and they have not failed (yet). A friend of mine has been experimenting with both Software based Raid O & 5 And the same with a PCI RAID controller. In his testing there seems to be a bottleneck at the PCI limiting his read/write speeds. Same drives in the same setup can achieve faster read/write speeds with the software based RAID (mostly when using 3 or more drives). It seems 150MB/s is the max on his PCI where he was able to get up to 240MB/s with 4 drives in a RAID 0?

I repeat I am new to all this so please correct me on anything I am saying. My thoughts are there are no real advantages with the RAID 0 (striped) because you are limited by what you are writing to or from. I understand if you were copying to or from multiple sources (I do have 2 external ESata ports) the RAID may handle the faster read/write in that situation. Most of the time I am only writing to a single non raid hard drive (either internal or external) and am limited by that drives read/write speed?

What advantage does the speed of RAID 0 have, what uses or aplications for the average user would this benefit. If I ever have to do a fresh install I am considering not going with RAID the next time around unless I am missing something?

 

[Dwarf]

Here is a link that you might find useful. RAID - Wikipedia, the free encyclopedia

 

[Dane]

Thanks for your input guys... I now have a better understanding then I did before...

 

[Ex_Brit]

Do you think they'd laugh at me if I asked for a non-RAID setup when ordering a machine from Alienware?
(It isn't an option when ordering online but I would imagine one could get it by phoning instead).
The reason I'm cagey about RAID is that I read so many tales of misery when people are trying to reinstall or repair their systems and some RAID driver or other is missing that has to be installed first. Plus with RAID 0 an HDD or RAID controller failure causes a total loss of data.
I would just like what I have now. Plain old SATA HDD's whose total capacity is available to me whenever.

 

[CyberZeus]

I was told ones that you should be careful with "Raid 0" since a failur on one of the diskes destroys all the data on both diskes, and that failurs occur more frequently in "Raid 0" then they would in non Raid setups.

If the likelihood of a given disk model failing within the year is say 10%, then using two of them in a RAID 0 stripe set increases the failure risk to 19% ( 1 - [0.9]^2 ). Three of them in the stripe set, and the risk goes up to 27.1, and so on...

Strictly speaking, RAID 0 is not RAID at all. There is no Redundancy in that configuration.

Also if a normal disks fails you have a chance to recover the data with some software, this is not true for the raid setup... Or am I wrong?

In both cases, it depends on what exactly failed. If it's a complete failure at a hardware level, recovery software ain't gonna help either way. If the partition definition is somehow damaged, or the file system metadata, then assuming there's nothing wrong with the underlying hardware the data is potentially salvageable in both instances.

Is there not a setup where you run two diskes like in "Raid 0" and have one extra disk for mirroring? Maybe Raid 2 or something...

Sure, you can mirror two RAID 0 sets, and that goes by a variety of technically-incorrect names

Most larger hardware RAID arrays use RAID 5 as the basic building element. Again, it's a stripe set, except that for any given stripe across the disks one of the disks contains only parity information which can be used to reconstruct the original data should any single disk fail. The setup is truly "redundant" in the sense that it is fault tolerant. With massive hardware controllers it can come close to providing the speed of RAID 0 while still being as safe as RAID 1 - two disks must die (without replacement) before the data is completely lost.

With RAID 5, assuming n as the number of drives involved and size as the size of the smaller disk, you have (n - 1) * size space for data. By the way, parity information isn't contained in only one disk, but in every 1 / n portion of every disk. So if you have 3 disks, every third of every disk contains parity information.

 

[Martee]

Hello Exbrit,

Do not worry about the RAID0 setup, I'm running it without any problem. I guess the important thing is to create raid with two brand new drives, not just to add the new one to old drive and make them run in raid.
Btw, you can always break the raid setup and set your disks in the conventional one, if you worry about your data and the Alienware sell machines with raid, only. The most important thing when you have the RAID0 is to make the frequent backup.

 

[Ex_Brit]

Hello Exbrit,

Do not worry about the RAID0 setup, I'm running it without any problem. I guess the important thing is to create raid with two brand new drives, not just to add the new one to old drive and make them run in raid.
Btw, you can always break the raid setup and set your disks in the conventional one, if you worry about your data and the Alienware sell machines with raid, only. The most important thing when you have the RAID0 is to make the frequent backup.

Thanks, I guess I should "go with the flow", as they say, and adopt RAID. With RAID are there any things one has to be aware of if one is repairing or reinstalling Vista?

 

[H2SO4]

...
Most larger hardware RAID arrays use RAID 5 as the basic building element. Again, it's a stripe set, except that for any given stripe across the disks one of the disks contains only parity information which can be used to reconstruct the original data should any single disk fail. The setup is truly "redundant" in the sense that it is fault tolerant. With massive hardware controllers it can come close to providing the speed of RAID 0 while still being as safe as RAID 1 - two disks must die (without replacement) before the data is completely lost.

With RAID 5, assuming n as the number of drives involved and size as the size of the smaller disk, you have (n - 1) * size space for data. By the way, parity information isn't contained in only one disk, but in every 1 / n portion of every disk. So if you have 3 disks, every third of every disk contains parity information.

I normally love being out-nitpicked

However, in this case we both said the same thing - for any given stripe one of the disks contains parity info.

 

[CyberZeus]

...
Most larger hardware RAID arrays use RAID 5 as the basic building element. Again, it's a stripe set, except that for any given stripe across the disks one of the disks contains only parity information which can be used to reconstruct the original data should any single disk fail. The setup is truly "redundant" in the sense that it is fault tolerant. With massive hardware controllers it can come close to providing the speed of RAID 0 while still being as safe as RAID 1 - two disks must die (without replacement) before the data is completely lost.

With RAID 5, assuming n as the number of drives involved and size as the size of the smaller disk, you have (n - 1) * size space for data. By the way, parity information isn't contained in only one disk, but in every 1 / n portion of every disk. So if you have 3 disks, every third of every disk contains parity information.

I normally love being out-nitpicked

However, in this case we both said the same thing - for any given stripe one of the disks contains parity info.

Not exactly: a part of all disks contains parity info.
Sorry, I didn't want to out-nitpick you...

 

[H2SO4]

I normally love being out-nitpicked

However, in this case we both said the same thing - for any given stripe one of the disks contains parity info.

Not exactly: a part of all disks contains parity info.
Sorry, I didn't want to out-nitpick you...

No need to be sorry at all. If someone is wrong, the technical mistake should be pointed out - it's a technical forum and reliability of info is important. Hence, please don't ever be bashful about correcting mistakes in anything I've written

Now to clarify why I think we're saying the same thing...

A "stripe" in this context means a linear path across all disks in a RAID0/5 array whose width is implementation-specific. For example, if the implementation relies on 64KB chunks, a "stripe" is comprised of 64KB on disk 0, 64KB on disk 1, 64KB on disk 2, and 64KB on disk N. In a RAID 5 array, one of the disks contains parity info for each stripe but that doesn't mean it's always the same disk for all stripes. (In fact, that would make it RAID 3 which has some advantages but that's a different story).

Collectively, all of the "stripes" are known as the "stripe set" but those two names (in quotes) are not synonymous. I think you may have read "stripe set" into my use of "stripe".

 

[Martee]

Hello Exbrit,

Do not worry about the RAID0 setup, I'm running it without any problem. I guess the important thing is to create raid with two brand new drives, not just to add the new one to old drive and make them run in raid.
Btw, you can always break the raid setup and set your disks in the conventional one, if you worry about your data and the Alienware sell machines with raid, only. The most important thing when you have the RAID0 is to make the frequent backup.

Thanks, I guess I should "go with the flow", as they say, and adopt RAID. With RAID are there any things one has to be aware of if one is repairing or reinstalling Vista?

There is nothing to worry about. The Raid setup is treated the same as the single drive, you can partition it the same way, installing or repairing operating system is the same. Once the ride is made you can forget about it and enjoy it. It's faster then the single hard drive in reading and writing data.

I created four Raid Volumes. The first one for the Operating System, Documents, and Programs. The second is used for Recovery, I store the image of the OS over there. The third and fourth partition is for my data, media including pictures, music, videos and such.
The first Volume I set to Raid 0, Stripe Size: 16kb, it's about 50 GB large. The rest Volumes are set to Raid 0, Stripe Size: 128kb, the recovery is 17GB large and the rest two partitions is about 432GB each.

 

[Ex_Brit]

I can see that I'm going to have to do a lot of reading about this. Thanks for the information. Is the speed gain really worth all this fuss?

 

[Martee]

I can see that I'm going to have to do a lot of reading about this. Thanks for the information. Is the speed gain really worth all this fuss?

I'm not the expert, but I think so. What I can say, it's really fast when I convert the audio or video files to another formats.

 

[Ex_Brit]

I guess it depends what one does the most on the machine. I'm thinking of an Alienware machine for reasons other than gaming and music/video processing, although I will be doing some of that. I have a lot of CPU intensive shared computing applications which, at the present time, have to throttle back when I'm doing other things. On a Core i-7 rig it should be a breeze to do a lot more simultaneously. Plus I have work that I do that is also resource hungry.
Plus their machines are extremely well put together if not slightly overpriced.