RAID Questions... Doesn't anyone know anything about RAID 5?

[Ilmater]

Some easy RAID questions for anyone who knows more than I do about RAID. Last time I posted these questions I got no responses, so I'm hoping to get a little more this time. What can I say, I'm an optimist. Anyway, I'd like to set up a RAID 5 array, but I need to know a few things.

• Can a RAID 5 partition be bootable?

• Is it a good idea?

• Which file system is best? Do you have to use NTFS? Do I have to use FAT32? I use NTFS currently and GREATLY prefer it.

• How many drives are common/possible for this setup?

• Assuming 4 is an acceptible number of drives, how much room would I have left with 80GB hard drives?

• Would it make much difference going with regular 7200 RPM WD's (800BBs) rather than 800JBs with the 8MB cache?

• Would it be better to go with smaller or larger drives?

• Recommendations on stripe size?

• Recommendations on partition size?

• Recommendations on a good controller? Promise? I don't think Highpoint makes a RAID 5 controller.

By the way, I'm not Ted Turner, so I have no intention of using SCSI in case that makes any difference in answering any of the above questions. I really need to figure these things out so that I can get buying, so all of your help is greatly appreciated.

 

[Jmmsbnd007]

Originally posted by: Ilmater
Some easy RAID questions for anyone who knows more than I do about RAID. Last time I posted these questions I got no responses, so I'm hoping to get a little more this time. What can I say, I'm an optimist. Anyway, I'd like to set up a RAID 5 array, but I need to know a few things.

• Can a RAID 5 partition be bootable?

• Is it a good idea?

• Which file system is best? Do you have to use NTFS? Do I have to use FAT32? I use NTFS currently and GREATLY prefer it.

• How many drives are common/possible for this setup?

• Assuming 4 is an acceptible number of drives, how much room would I have left with 80GB hard drives?

• Would it make much difference going with regular 7200 RPM WD's (800BBs) rather than 800JBs with the 8MB cache?

• Would it be better to go with smaller or larger drives?

• Recommendations on stripe size?

• Recommendations on partition size?

• Recommendations on a good controller? Promise? I don't think Highpoint makes a RAID 5 controller.

By the way, I'm not Ted Turner, so I have no intention of using SCSI in case that makes any difference in answering any of the above questions. I really need to figure these things out so that I can get buying, so all of your help is greatly appreciated.

I'm no RAID expert, but I'll try to answer some of these. A RAID 5 partition should be able to be booted from. I don't see why it wouldn't be a good idea. NTFS should work just fine. I'd go with the 8MB cache ones, although I haven't heard how they perform in RAID. I'd go with large drives, as you have plenty of redundancy. Now... answer some of mine What is a stripe? And why did you choose RAID 5 over 0+1? /me is sort of a RAID n00b...

 

[GoSharks]

>Can a RAID 5 partition be bootable?

yes, but you will have to setup your bios so that it boots from an external source instead of the onboard ide controllers. usually it is the scsi choice, or raid choice if you are using built in raid on the mobo.

>Is it a good idea?

depends on what you are using it for. do you need fast writes? if so, i would look towards raid 1, but you would need more drives to have the same amount of space.

>Which file system is best? Do you have to use NTFS? Do I have to use FAT32? I use NTFS currently and GREATLY prefer it

you can use raid with any filesystem you wish.

>How many drives are common/possible for this setup?

common? probably 3? not sure. 4 is fine.

>Assuming 4 is an acceptible number of drives, how much room would I have left with 80GB hard drives?

when using raid5, you lose one drive in capcity, (n-1) where n is the number of drives you have in the array. with 4 80gb drives, you will have 3*80gb, or 240GB.

the other questions are better left to the others...

 

[amdskip]

here's a good link!

 

[FluxCapacitor]

Ilmater:

I can tell you all about RAID5, but the first question I have to ask is, why?

RAID5 controllers are NOT cheap, NOT exceptionally fast (compared to an individual disk or RAID 0), and require you to purchase RAM (normally) in order for them to work. What the ARE good for is redundancy and data accessibility, meaning time lost during a hardware failure is much less. We're not talking about software RAID here either (although it is possible). RAID 5 is normally hardware based. I wouldn't recommend it unless you're running a server type setup where you need a high degree of redundancy in case of disk failure. Such as, you have 1000 users on your business network that can't wait around for you to rebuild the server if a disk crashes. Now keep in mind RAID 5 is not bulletproof. You can STILL lose data on the array through a virus, massive disk failure (more than 1), hardware failure, etc... although this possibility is greatly reduced when using RAID 5.

But if you still have your heart set on RAID 5, here's the answers to your questions:

Can a RAID 5 partition be bootable?
Yes, a RAID5 partition can be bootable, just like any other RAID partition.

Is it a good idea?
It is neither a good nor bad idea. It makes no difference. If you're using RAID 5 though, it doesn't make any sense to have a non-RAID 5 partition running.... it basically negates the purpose of having the array to begin with. (Unless you used it for backup, but most people with RAID 5 arrays use tape drives for backup, as it keeps your information seperate in case of lightning, theft, virus, etc)

Which file system is best? Do you have to use NTFS? Do I have to use FAT32? I use NTFS currently and GREATLY prefer it.
A RAID array does not care what file system you use on it, just like your individual hard drive doesn't care what file system you use. If you prefer NTFS, go for it.

How many drives are common/possible for this setup?
Minimum required is 3, up to a maximum supported by the controller (often 4 or 6 for ATA controllers)

Assuming 4 is an acceptible number of drives, how much room would I have left with 80GB hard drives?
Array size on RAID 5 is (number of drives - 1) x (size of smallest drive in the array)

In your example it would be (4-1) x 80GB = 240GB

Basically, in a RAID 5 setup, having more drives is better than less, as your total wasted space is smaller.

Would it be better to go with smaller or larger drives?
Makes no difference. My answer to the last question pretty much covers why.

Recommendations on stripe size?
Not a real big issue. Most RAID 5 controllers don't have a lot of options anyway from what I've seen. You're probably better off sticking with the default, although I'm sure some people would agrue otherwise.

Recommendations on partition size?
I think you're confused between "array size" and "partition size"

Creating an array is not like creating a partition using fdisk or disk manager. For instance, I could create a 200GB RAID 5 array, using your example above of 4 80GB drives. As far as my operating system is concerned, I now have a 200GB hard drive that (Windows sees it as 1 single drive) that I can partition into as many logical drives as I want to. I could make it into 4 50GB partitions if I want. It makes no difference to the RAID array.

Where you might be confused: You can't pick a portion of a drive to add to the RAID 5 array, which is what you might be thinking. It's all or nothing, as in "do I want this 80GB drive to be part of the RAID array or not". You can't split a hard drive up between different RAID arrays. Also, it would make no sense to have more than 1 RAID 5 array unless you had seperate controllers running seperate arrays because you maxed out the capacity of the one controller.

Recommendations on a good controller? Promise? I don't think Highpoint makes a RAID 5 controller.
Well, first off, RAID 5 cards are quite expensive. Both Promise and Adaptec have RAID 5 IDE cards, but both are over $350, not including any RAM you may need to buy for the controller. And no, that's not a lot for a RAID 5 card. HighPoint does not have any IDE RAID 5 controllers.

Well, there you go. Hope that helps. Anymore questions, just ask.

 

[Zugzwang152]

Might also want to check out the AT FAQ section. There's good descriptions of IDE-RAID solutions, and you might find something that will work better for you.

 

[Ilmater]

First off, thanks again for the replys. The reason I'm going with RAID 5 is basically reliability with the added speed on the side. My friend was running on an 80GB IBM Deskstar that crashed a couple of months ago. He lost the 50GBs of "files" on his hard drive. That problem was actually compounded by the fact that the 80-some-GB of "files" that he had backed up were the ones I already had. Thus, the two of us lost those files for good. I don't want that to happen to my stuff, as I currently have 300GB of hard drive space that is starting to fill up. I can't possibly count the months that it took to pull all of these "files" together and definitely don't want to lose them all. BTW, "files" includes MP3s, every Family Guy episode, a growing collection of Simpsons (which will go away as soon as the DVDs all come out), various CD images that I've backed up in case they get scratched beyond repair (I try to keep them clean, I really do)... all kinds of stuff. I would back them up to a cd, but as I just mentioned, I don't want to lose information to scratches and simple wearing-out. I backed up 37 CDs worth of my MP3s (all legitimately copied from CDs I paid for, I swear) before and, when I bought a new hard drive and decided to store them there instead of separate CDs so that I could easily choose one album or another, I found that many were terribly scratched and about half-a-dozen had labels that were peeling off! I lost a lot of music that took months to get back and I don't want to think about what might happen if my hard drive crashes.

Now that that's been said, I understand that RAID 5 isn't 100% fool-proof, but I don't see it being neccessary to prepare for what would happen if more than one hard drive went out at once. 0 + 1 is nice, but it means I'd have to up the count to 8 drives to get the same amount fo storage I currently have. My only other option would be to use 4 drives, and that would mean one of two things: I'd only have 160GB of space, or I'd have to switch to 120GB hard drives and still only have 240GB of space. If there were a good, alternative source of backup, I'd be there. However, with tape drives being way too small, I don't have that option. CD's would be nice, but I'm not sure what I'd do if my Jimi Hendrix or Black Sabbath collections (both as extensive as they come) suddenly didn't work. Therefore, a RAID 5 array was the only real choice for me.

So, having said that, let's back to my original quesitons. Most were answered by people here, and the stripe size question was answered by amdskip's link. The only questions I have left are:

• What is the best partition size for my array? I understand that I have to use entire drives, but I understand that how I partition those drives is important in determining how fast they operate, which brings me to my next question...

• Assuming that I keep these drives defragmented, how much performance difference would I get from partitioning? I'd rather just use one big partition if the performance gains aren't large enough.

• Are thre alternative methods to backing up all 300GB of data that don't include CDRs? How big are tape drives nowadays?

• The last (and most obvious) question: is there much of a performance gain/loss from RAID 5? Does it have much higher CPU utilization than a single drive?

 

[Mavrick007]

It's true that Raid 5 must have a minimum of 3 drives to implement. Here is a good site on Raid 5, as well as the other types of Raid available. It tells you Pros/Cons to each setup.

Tape drives are getting pretty large now and you can find some that will do 100Gigs of data backup or more. I would suggest either tape drives, or possibly getting some hard drives and copying everything over onto them and then just storing them out of the case in a safe, clean and dry area. It will cost you less than the Raid 5 card and setup alone and you'll have less confusion as well as redundancy in case something goes down.

These are just some ideas, but then again you could always buy a dvd burner and store even more per disk so that the cost goes down and you could always make a couple of copies (1 to use and scratch up and 1 as a master to make copies from).

 

[DaveSimmons]

Cost-wise it seems better to go with no RAID at all, and use one IDE channel (or buy a cheap non-RAID IDE controller) together with removable HD trays. One "holder" in your tower could be used with an unlimited number of trays, swap in 1, fill up 120 GB of files, swap it out for another one, stack them up on a shelf. Cost-wise you get the first 240 GB for less than the price of the RAID controller, even before you buy the RAID parity and mirror drives.

 

[Ilmater]

I disagree. A RAID 5 setup with a total of four (I already own one) WD 80GB special edition hard drives would cost $596 shipped (don't question my math, just trust me, straight from Pricewatch). The only other two realistic options would be to get 4 80GB hard drives (I have 300 GB to back up) for $336, or get a DVD burner and discs for about $304. The DVD burner is just ridiculous, as it would take at least 64 discs to burn and that takes WAY too long. The 4 80GB hard drives take more money and give me no increase in speed (just like the DVD burner).

 

[Alkali]

I would like to expand my present setup into a RAID 0+1 or RAID 5 setup using 5 WD800JB's (for usable 320GB space). Reason for my only having one drive at the moment is that all my other data is stored over the LAN while I'm upgrading this machine

Can I just ask, If you have either RAID mode enabled, does EVERY RAID controller automatically rebuild a lost HDD's data on the fly using the remaining discs (or later when you replace it)? - In other words, I am far from a RAID expert, want RAID, but am very unsure of the technology if I've got to do lots of configuring and command line rubbish...

Regards...

 

[Alphazero]

Originally posted by: Ilmater

• Can a RAID 5 partition be bootable?

Yes, just like any RAID array.

• Is it a good idea?

Depends on whether you need it. If you do need redundancy and better performance, RAID 5 is generally better than 0+1, but redundancy takes a hit because only one drive can fail.

• Which file system is best? Do you have to use NTFS? Do I have to use FAT32? I use NTFS currently and GREATLY prefer it.

Boxers or briefs? NTFS will offer you compression, encryption and security options. Generally better, but not necessary if you already have FAT32 (and don't need those features, of course).

• How many drives are common/possible for this setup?

3 or more.

• Assuming 4 is an acceptible number of drives, how much room would I have left with 80GB hard drives?

3x80 = 240GB

• Would it make much difference going with regular 7200 RPM WD's (800BBs) rather than 800JBs with the 8MB cache?

Not much, but it may be noticeable.

• Would it be better to go with smaller or larger drives?

Many small drives will be faster, but more expensive and more prone to failure.

• Recommendations on stripe size?

RAID 5 is done bit by bit.

 

[Ilmater]

Wait a minute, I'm pretty sure that that's wrong. RAID is done block by block. RAID 3 is byte by byte. RAID 4 goes up to block by block. Then, RAID 5 steps up to moving each parity section across the drives.

However, that's not my real problem. My problem now is, what partition sizes should I use?

 

[Alkali]

I read the links you guys gave above, but I'm still not sure if RAID 0+1 or RAID 5 is my best choice... The thing I'm most worried about is loosing a drive, and it messing everything up - I heard a long time ago, that the controller cards can rebuild 'on-the-fly' if you have a redundant drive.

If a disc fails, will any controller that supports these RAID levels use a redundant drive (if I used the 5th drive as such) to rebuild the lost drive?
Which RAID level (from 0+1 or 5) is best suited to rebuilding easily upon a single disc failure?

Regards