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Why raid?

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August 16, 2006 10:59:21 PM

If I have two 300gb HD's in RAID 0 then my system looks at it as one 600gb drive, right? I forget what raid 1 and 2 are, but my question is this: What is the advantage in a RAID setup as opposed to installing the drives and have one as your "c" drive, and the next as a "d" drive, etc, like we did before raid?

Thanks!

Eddie

More about : raid

August 16, 2006 11:44:33 PM

Don't anyone DARE waste a single minute providing detailed answers to Mr. I-can't-use-Google.

For goodness sake man, there are literally HUNDREDS and probably THOUSANDS of pages which have EXTEMELY detailed information about RAID and how it works, along with pros and cons of each RAID mode.

In my opinion, RAID can NEVER be justified on a desktop PC. In a workstation, perhaps, in a server: definitely.

However, in your case, you are too stupid and too lazy to be trusted with something like RAID. So just give it up, OK?

If you want faster drives, buy Raptors, and save yourself from a nightmare.
August 17, 2006 12:24:35 AM

There's a RAID FAQ along with many threads on the subject in the Hard disk forum. That should get your started.
Related resources
August 17, 2006 2:22:32 AM

You're being quite harsh, Mobius. I did google about RAID and also went to wiki. My question is why? If you have 2 drives in RAID 0 and one crashes, you lose data on both drives. From what I read RAID 1 automatically copies your data from one disk to the other...correct? But my question is what is the advantage of having your two 300gb drives acting as one 600gb drive instead of having 2 different drives?
August 17, 2006 3:06:23 AM

Quote:
In my opinion, RAID can NEVER be justified on a desktop PC.


And you have a right to your opinion, no matter how screwed up it is.

Fortunately, I don't have to look to you to approve the setups I choose for my own rigs.
Anonymous
a b G Storage
August 17, 2006 3:19:20 AM

your theoretical setup of two 300g drives when used as Raid 0 provides a total of 600gb of storage, with a mibor imrovement in I/O performance, better speed, but not significant. This is accomplised by Raid deciding which drive to write to or read from based on which one can access information faster. Your correct, one dies, both are dead, because date is files are split into chuncks of data sent to the first available drive.

Raid 1 would only provide a total of 300g because both drives are mirrored (exact copy of each other). So if one drive fails you do not lose any data.

So unless you want a minor increase in speed or don't want to lose data, raid is not your solution. Stick with 2 IDE or SATA drives.

There are other combinations of raid, such as 0+1, 5, 10.

Bottom line, if your not serious enough to do the research to determine if Raid meets your needs, Don't waste your time.
a b G Storage
August 17, 2006 3:59:10 AM

Quote:
Don't anyone DARE waste a single minute providing detailed answers to Mr. I-can't-use-Google.

For goodness sake man, there are literally HUNDREDS and probably THOUSANDS of pages which have EXTEMELY detailed information about RAID and how it works, along with pros and cons of each RAID mode.

In my opinion, RAID can NEVER be justified on a desktop PC. In a workstation, perhaps, in a server: definitely.

However, in your case, you are too stupid and too lazy to be trusted with something like RAID. So just give it up, OK?

If you want faster drives, buy Raptors, and save yourself from a nightmare.


Wow, now there's a friendly reply if I ever heard one. Since Google is so great, and we can find facts about everything we ever need to know already somewhere on this forum, they should just shut down all new posting and and label it "Toms Hardware Database"
Then no one will ever again feel compelled to answer all these petty questions.
If ya don't want to answer someone's question or think it's stupid because you already "know everything", then just move on to the next thread. No one is bending your arm and forcing you to type.

Yeah, and I have RAID 0 on my machine. I happen to think it was well worth the time and money to set it up. Would never go back to a single drive.
I figure your valuable opinion is worth about 2 1/2 cents. You got change for a nickel?
August 18, 2006 3:07:02 PM

A RAID 0 Win2k software configuration will make the transfer rate significantly higher. If you have each drive running as master on separate channels, you can expect an 70-80% increase in data transfer rates.

So if your working with gigabyte files all the time (media files), then RAID 0 is ideal. The disadvantage is that if one drive fails, then all your data is lost. If you want speed and performance, you'll need RAID 5 or RAID 10.

Without RAID, if your C drive dies, then you still have everything in your D drive.

For everyday work where you deal with small to medium sized files, I don't see any advantage of using RAID 0.
August 18, 2006 3:42:49 PM

To me a desktop is the ONLY place RAID 0 can ever be justified.

Servers should be using RAID 1, 0+1, 3, 5, 6 only.

I have three 120GB sata disks on a RAID 0 array as my C drive. They have been there years. None of them have broken (though they are well cooled).

Even if one did die, I'd reduce the array to 2 disks and spend some time reinstalling windows, then reinstall the other programs I want from my storage drive.

It really wouldnt be the end of the world to me, and modern hard disks have a massive MTBF if cared for properly.
August 18, 2006 4:21:19 PM

Quote:
your theoretical setup of two 300g drives when used as Raid 0 provides a total of 600gb of storage, with a mibor imrovement in I/O performance, better speed, but not significant. This is accomplised by Raid deciding which drive to write to or read from based on which one can access information faster. Your correct, one dies, both are dead, because date is files are split into chuncks of data sent to the first available drive.

Raid 1 would only provide a total of 300g because both drives are mirrored (exact copy of each other). So if one drive fails you do not lose any data.

So unless you want a minor increase in speed or don't want to lose data, raid is not your solution. Stick with 2 IDE or SATA drives.

There are other combinations of raid, such as 0+1, 5, 10.

Bottom line, if your not serious enough to do the research to determine if Raid meets your needs, Don't waste your time.


The speed increase from RAID 0 is actually significant. about 50-80% depending on read or write.

RAID 0 is striping, it doesn't randomly send data to one or the other, it splits data up into "chunks" which are sent in an orderly fashion to one disk or the other, and this is faster because as one drive is reading or writing, the other drive is either receiving, preparing, or also reading and writing at the same time. A lot of the speed increase is due to being able to use 2 read/write heads simultaneously. It's not a 100% increase in speed because there is some processing overhead at the controller

If you lose a drive, yes you lose all your data. And technically the risk is higher than a single drive because simply, there are 2 drives that might fail. But statistically, the MTBF on hard drives is so high, it's virtually not a factor. Think 300,000 hours on a single drive. With 2 drives, the risk doubles, and MTBF drops to 150,000 hours (a little over 17 years). That's still a damn long time.

Is RAID 0 overkill for desktops. I dont' think so. It is undeniably significantly faster than a single drive. And the risk is fairly small, even if you expect your drives to last 5-8 years, which I do.

RAID 1 is mirroring, meaning all data is written to both drives identically. This one is far less common than RAID 0 because it's expensive (need 2 drives and you get only half the total nominal storage) and because most people don't have a need to store data that securely. Most COMPANIES don't have a need to store data that securely (and if they did, they'd probably be using RAID 5 anyways).

For a consumer, the two flavors of RAID that are really useful in my opinion, is RAID 0 for the speed, and RAID 5 for the increased speed (not as fast as RAID 0) and redundancy (pretty safe but not exactly as good as RAID 1).

You'll need to read up on the technical details on RAID 5. I don't think anyone will want me to write up that level of detail here. Suffice to say RAID 5 is also known as Striping with distributed parity.
August 18, 2006 4:33:49 PM

One of the other important aspects to recognize about RAID is that RAID is (generally) all about improvement in transfer rates or hardware redundancy (or both), however it doesn't do anything to make Windows any more stable or reliable. As many here have stated before, RAID-0 will provide you with faster access, but if either drive fails, you're dead in the water. RAID-1 will provide you with a second copy of your drive (mirroring) so that way if one drive fails, you have all your data on a second drive and can recover quickly enough. And there are plenty of additional RAID types and levels (0+1, 3, 5, and so on) that provide various types and levels of transfer rate increase, data redundancy and/or data parity.

As stated above, however, RAID does not protect against Windows doing something screwy. For example, let's say you have a RAID-1 setup (mirroring). Again, this means you have an exact copy of your drive. However if Windows decides to destroy its registry (which has actually happened to me before), it will wreak that havoc on BOTH drives, meaning NEITHER of them is now bootable. Yeah, you can still get the data off of them by slaving them to a clean drive, but the point of that redundancy is now lost because it wasn't the hardware that failed you but the operating system. RAID controllers are not smart enough to know "Hey, that's a really dumb thing the OS is doing to itself, I'm not going to let it do that to the mirror drive."

So even in the case of RAID 1 or 5 or any other mirrored/parity level, you cannot protect against Windows doing something universally stupid--and this may come as a shock to you, but Windows has been known (once or twice) to do something like that.

I've spent money on reasonably good consumer-level RAID cards (including caching controllers) as well as motherboards with high-end RAID chipsets integrated onto them, good stable RAID drivers and so on. It is certainly true that selecting the right RAID chipset or RAID card can absolutely improve performance and reliability, even those dollars won't make Windows less likely to mess itself.

When I think about the number of hard drives I've actually had fail me versus the number of times I've seen Windows destroy itself in one way or another, I would guess that Windows is far more likely to "fail" before a hard drive will bite the dust. Not that hard drives don't die, mind you, just that they are less likely to die before Windows does something colossally moronic to itself.

As I build systems today, I look at RAID, smile at it, even wave to it as I piece my new systems together, but I skip using it if I am building a desktop machine. Servers, certainly (RAID-0 for the OS/boot drive, RAID-1, -0+1, or -5 for the data drives, depending on number of drives/amount of data/size of data), but not desktops. In my own opinion, the benefits of using RAID on desktops--while measurable--do not outweigh the disadvantages (or more precisely the potential downfalls).
August 18, 2006 4:39:29 PM

Okay, let's be clear:
1) Physical drives are not partitions and are not logical drives
2) RAID while the first letter means Redundant isn't really Redundant in RAID 0

With those out of the way, let's cover a few basics:
1) RAID 0 is great if you need high performance, but have backups incase any of your drives crash (RAID 0 is not limited to 2 drives, but can be more depending on your drive controller)
It basically works by alternating storage on the # of drives you have. 10 drives mean each drive gets 1/10th the data in alternating fashion. So a 1MB file is stored on 10 drives (could be different depending on the size of the alternating chunks, but just keep the example simple)
2) RAID 1 is great if you need good read performance, write performance can be lower depending on bus saturation, and the controller. It gives the benefit of a single drive failure can be repaired by simply swapping out the failed drive (sometimes the machine must be powered off for the swap). Reason why you get better read performance is the data is stored 2x and can be read from both places
3) RAID 0+1/1+0 are striped mirrors, or mirred stripes. Basically, a combination of the above 2. If you have enough bus speed, and drive controller speed, you basically have the fastest configuration you can get, while getting redundancy.
4) RAID 5 - Parity raid. Alternating sections of parity (checksum) data is stored on each drive in different sections. If a drive goes down, the data either exists for real, or the parity does, in which case it can be repaired. Because of the parity, only 1 drive worth is used for redundancy, but the XOR feature lowers performance somewhat. Also drive performance usually suffers alot when a drive is down. Two drives and you are toast.
5) JBOD - 2 or more drives concatenated (one added to the end of the other) to make more storage. Other than extra storage, you don't get much benefit.
6) Hot spare - empty drive to jump into a RAID when one fails. Won't help RAID 0, but can help other kinds.

There are other raids, but I don't figure you need them since you seem more enthusiast level.

Even with redundancy, your backup liability is not removed!

In addition, there are caveats, like your system must have drivers for your raid controller installed to be able to boot off it. Sounds wierd that it can read the drivers off the drive that it needs the drivers to boot from, but that's Windows for you. In any case, if you have a regular Windows XP setup, you will basically need to add the drivers into the system at install time, or prior to your upgrade. If you don't know how to do this from experience, be prepared for potential frustration.

Hope this helps,

John
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