Explain raid to an idiot
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RAID: Redundant array of independent disks. It's a way of making several hard drives work together, either to act as one big hard drive, or to create duplicate copies in case one fails. There are several different setups to use, and it can be fairly easy or fairly difficult depending on the hardware you use. More info on the Wikipedia page:
http://en.wikipedia.org/wiki/RAID
http://en.wikipedia.org/wiki/RAID
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Hmm. How a hard drive works is considerably more complex than RAIDing them together...
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Wikipedia is a good place to start, but even more simply you can look at RAID as a way to overcome some of the disadvantages of hard drives. You use different levels (or types) of RAID to overcome different disadvantages, and each level has it's own pros and cons.
Very briefly, the common levels:
RAID0 - writes little bits of data to more than 1 disk in turn. As a result you get higher speeds, as you read/write data simultaneously to multiple disks. You also get higher capacity, as you get multiple disks presented together as 1 drive.
The disadvantage is the higher failure rate - one disk dies, everything goes.
RAID1 - mirrors 2 drives so both hold the same data. Main advantage is you keep your data if one drive fails. Disadvantage is it costs twice as much (have to buy 2 disks) for no increase in capacity and no real performance change.
RAID10 - a combination of RAID1 and RAID0. Needs 4 disks, offers the advantages and disadvantages of each.
RAID5 - Writes chunks of data to each disk as in RAID0, but now also writes a little bit of data that can be used to recalculate any of the other bits in each chunk. Means if a disk fails you can still use the array. Often seen as a 'best of both worlds' between RAID0 and RAID1, as you get better performance, some failure tolerance and still retain high capacity, although in reality it is much more complex than this. You get the capacity of all but one of your disks added together. The main disadvantage is the high cost of the controller and high overheads for certain operations.
RAID6 - like RAID5, but can survive 2 disk failures, but at the capacity loss of 2 drives.
That will do for starters, you are better off reading wiki and asking some more specific questions than having people try and explain RAID entirely...
Note that this quick post ignores things like using different sized or mismatched disks and doesn't really go into all the pros and cons for each level, but is just a quick intro...
(Note also that RAID0 is not really a RAID level at all - see the above post for the RAID definition - no redundancy here, so not really RAID at all, but it's the most common level you will see on this forum at least...)
Originally Posted by james...  Assume I know nothing about raid. Obviously I know how a hard drive works, so you can assume that. 
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Wikipedia is a good place to start, but even more simply you can look at RAID as a way to overcome some of the disadvantages of hard drives. You use different levels (or types) of RAID to overcome different disadvantages, and each level has it's own pros and cons.
Very briefly, the common levels:
RAID0 - writes little bits of data to more than 1 disk in turn. As a result you get higher speeds, as you read/write data simultaneously to multiple disks. You also get higher capacity, as you get multiple disks presented together as 1 drive.
The disadvantage is the higher failure rate - one disk dies, everything goes.
RAID1 - mirrors 2 drives so both hold the same data. Main advantage is you keep your data if one drive fails. Disadvantage is it costs twice as much (have to buy 2 disks) for no increase in capacity and no real performance change.
RAID10 - a combination of RAID1 and RAID0. Needs 4 disks, offers the advantages and disadvantages of each.
RAID5 - Writes chunks of data to each disk as in RAID0, but now also writes a little bit of data that can be used to recalculate any of the other bits in each chunk. Means if a disk fails you can still use the array. Often seen as a 'best of both worlds' between RAID0 and RAID1, as you get better performance, some failure tolerance and still retain high capacity, although in reality it is much more complex than this. You get the capacity of all but one of your disks added together. The main disadvantage is the high cost of the controller and high overheads for certain operations.
RAID6 - like RAID5, but can survive 2 disk failures, but at the capacity loss of 2 drives.
That will do for starters, you are better off reading wiki and asking some more specific questions than having people try and explain RAID entirely...
Note that this quick post ignores things like using different sized or mismatched disks and doesn't really go into all the pros and cons for each level, but is just a quick intro...
(Note also that RAID0 is not really a RAID level at all - see the above post for the RAID definition - no redundancy here, so not really RAID at all, but it's the most common level you will see on this forum at least...)
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These videos sum it up quiet nicely
http://www.professormesser.com/free-...g/220-701/raid
http://www.professormesser.com/free-...g/220-701/raid
This site has pretty animations and explanations that make it simple to understand any raid level;
http://raid.com/04_00.html
http://raid.com/04_00.html
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Not true.
Raid 0 is great for getting the best performance out of a set of drives. I use it on all of my gaming rigs and have never had any issues. I have also used it on many SW build systems to help with compilation times.
Raid 0 is NOT good for fault tolerance.
Originally Posted by lblitzer Raid 0 is almost never a good idea. |
Raid 0 is great for getting the best performance out of a set of drives. I use it on all of my gaming rigs and have never had any issues. I have also used it on many SW build systems to help with compilation times.
Raid 0 is NOT good for fault tolerance.
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this just isn't true.
Originally Posted by lblitzer Raid 0 is almost never a good idea. |
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I think thats what he meant, or if he didnt, than this is what is actually true.
Raid is simply; using multiple drives as one "virtual" one, with different types of uses, RAID0 being "faster", Raid 1 being fault tolerance, so on so forth. wiki has good explanation of that part. What the raid controller is hardly worthwhile to memorize, but maybe you want to, unfortunatly i too know nothing of this.
Originally Posted by airbozo Not true. Raid 0 is great for getting the best performance out of a set of drives. I use it on all of my gaming rigs and have never had any issues. I have also used it on many SW build systems to help with compilation times. Raid 0 is NOT good for fault tolerance. |
Raid is simply; using multiple drives as one "virtual" one, with different types of uses, RAID0 being "faster", Raid 1 being fault tolerance, so on so forth. wiki has good explanation of that part. What the raid controller is hardly worthwhile to memorize, but maybe you want to, unfortunatly i too know nothing of this.
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Unless you like working with much higher risks than any of the other solutions. A lot of people also think that double the drives means double the performance. Really it just doubles the risk of failure.
Now don't get me wrong it does in fact increase performance, it's not worth it if you're not willing to have that chance of a drive failing, having to purchase another one, losing your information, and having to rebuild your array.
So yes, fault tolerance.
Originally Posted by DuckieHo You're backing up that statement with what? 
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Now don't get me wrong it does in fact increase performance, it's not worth it if you're not willing to have that chance of a drive failing, having to purchase another one, losing your information, and having to rebuild your array.
So yes, fault tolerance.
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I used Raid 0 for over 3 years with out any issues.
Though I would only use Raid 0 on a gaming PC, and not on a work PC with important documents.
Though I would only use Raid 0 on a gaming PC, and not on a work PC with important documents.
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RAID0 does increase sequential performance nearly linearly. It also does improve IOPs.
The risk of a failure is NOT doubled. The risk of failure is now just dependent on the drive that fails first. That would be the probablity of mostly independent events (mostly because of bad batches or PSU failure is possibility).
Worth is subjective. If the odds of failing are say 1% over a year, then it may be worth it to the enduser for the improvement in specific applications.
Fault tolerance is not a requirement for every single use.
Originally Posted by lblitzer Unless you like working with much higher risks than any of the other solutions. A lot of people also think that double the drives means double the performance. Really it just doubles the risk of failure. Now don't get me wrong it does in fact increase performance, it's not worth it if you're not willing to have that chance of a drive failing, having to purchase another one, losing your information, and having to rebuild your array. So yes, fault tolerance. |
The risk of a failure is NOT doubled. The risk of failure is now just dependent on the drive that fails first. That would be the probablity of mostly independent events (mostly because of bad batches or PSU failure is possibility).
Worth is subjective. If the odds of failing are say 1% over a year, then it may be worth it to the enduser for the improvement in specific applications.
Fault tolerance is not a requirement for every single use.
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Any body who is running without backups (whether your data is primarily on single disks, RAID0 arrays or on some form of redundant arrays), you should be expecting to lose some data sooner or later.
RAID in any form is no substitute for backup, but neither is running single disks. If you run 2 full drives of the same size together in RAID0 you are just increasing the chance you will lose everything rather than just half of your data - not really a good arguement that RAID0 is bad because of the data loss risk, as both scenarios involve losing information if it's not stored elsewhere.
Originally Posted by lblitzer Unless you like working with much higher risks than any of the other solutions. A lot of people also think that double the drives means double the performance. Really it just doubles the risk of failure. Now don't get me wrong it does in fact increase performance, it's not worth it if you're not willing to have that chance of a drive failing, having to purchase another one, losing your information, and having to rebuild your array. So yes, fault tolerance. |
RAID in any form is no substitute for backup, but neither is running single disks. If you run 2 full drives of the same size together in RAID0 you are just increasing the chance you will lose everything rather than just half of your data - not really a good arguement that RAID0 is bad because of the data loss risk, as both scenarios involve losing information if it's not stored elsewhere.
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Maybe not double but further increasing your chances for your array to fail. If one drive fails, then the entire array is gone.
But again, it's just the risk of doing Raid 0. I have yet to see a reason for me or anyone I know to use it (even gamers), but to each their own. I certainly don't have a problem waiting for programs to load because I grew up on old 300mhz systems that took anywhere from 30 seconds to 5 minutes to load a heavy program. :\\
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Exactly. I use Raid 1 as a backup right now and even then I've still got my more important data on a 3rd drive.
When I did field tech work, I couldn't stress to people how important it was to buy 2 or 3 more drives as backups because you can't put a price on their information.
Originally Posted by DuckieHo The risk of a failure is NOT doubled. The risk of failure is now just dependent on the drive that fails first. That would be the probablity of mostly independent events (mostly because of bad batches or PSU failure is possibility). |
But again, it's just the risk of doing Raid 0. I have yet to see a reason for me or anyone I know to use it (even gamers), but to each their own. I certainly don't have a problem waiting for programs to load because I grew up on old 300mhz systems that took anywhere from 30 seconds to 5 minutes to load a heavy program. :\\
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Originally Posted by the_beast RAID in any form is no substitute for backup, but neither is running single disks. If you run 2 full drives of the same size together in RAID0 you are just increasing the chance you will lose everything rather than just half of your data - not really a good arguement that RAID0 is bad because of the data loss risk, as both scenarios involve losing information if it's not stored elsewhere. |
When I did field tech work, I couldn't stress to people how important it was to buy 2 or 3 more drives as backups because you can't put a price on their information.
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You grew up walking from place to place too. Ever use a car now? Why? Surely walking is fast enough, since it was the only option you had when you were 10.
Why not get as much performance as possible if that is your goal?
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If you worked as a tech you should probably know the difference between RAID1 and backups then. They are not the same thing, and RAID1 does not protect like a proper backup scheme.
Originally Posted by lblitzer But again, it's just the risk of doing Raid 0. I have yet to see a reason for me or anyone I know to use it (even gamers), but to each their own. I certainly don't have a problem waiting for programs to load because I grew up on old 300mhz systems that took anywhere from 30 seconds to 5 minutes to load a heavy program. :\\ |
Why not get as much performance as possible if that is your goal?
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Originally Posted by lblitzer Exactly. I use Raid 1 as a backup right now and even then I've still got my more important data on a 3rd drive. When I did field tech work, I couldn't stress to people who important it was to buy 2 or 3 more drives as backups because you can't put a price on their information. |
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Which is why I said "to each their own".
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Not really when you're selftaught, have no background experience, and your job is replacing hardware and basic troubleshooting to the general population.
Originally Posted by the_beast You grew up walking from place to place too. Ever use a car now? Why? Surely walking is fast enough, since it was the only option you had when you were 10. |
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Originally Posted by the_beast If you worked as a tech you should probably know the difference between RAID1 and backups then. They are not the same thing, and RAID1 does not protect like a proper backup scheme. |
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...and that's not a reason NOT to use RAID0 if you understand the inherent risks.
Also, you're not screwed if you have backups/archives or don't care about the data that much.
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Yes, you do increase the probablity of failure but you can come close to doubling the performance in some cases. Why would you wait 5 mins when it could load in 3mins? If you save few minutes everyday for a year and you have backups/don't care, then cost-benefit says you SHOULD utilize RAID.
My first PC was 8MHz with 16 MHz Turbo Mode so I remember the old days.
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Originally Posted by 88EVGAFTW If one drive fails or get errors, you're screwed. |
...and that's not a reason NOT to use RAID0 if you understand the inherent risks.
Also, you're not screwed if you have backups/archives or don't care about the data that much.
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Originally Posted by lblitzer Maybe not double but further increasing your chances for your array to fail. If one drive fails, then the entire array is gone. But again, it's just the risk of doing Raid 0. I have yet to see a reason for me or anyone I know to use it (even gamers), but to each their own. I certainly don't have a problem waiting for programs to load because I grew up on old 300mhz systems that took anywhere from 30 seconds to 5 minutes to load a heavy program. :\\ |
My first PC was 8MHz with 16 MHz Turbo Mode so I remember the old days.
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RAID, Technology developed over 20 years ago primairly for use with servers and their data storage problems. RAID was a way to deal with ever failing hard drives. The technology is still in use today (even though drive quality has greatly improved) and has seen a new customer, people who wish the same benifits offered too servers for their home PC's
I bought a Dell Optiplex 330, it had two drives and they were in a RAID configuration.RAID was not developed for PC's with 2 drives, it has been co-opted for this application.Never did me any harm or any good.
I bought a Dell Optiplex 330, it had two drives and they were in a RAID configuration.RAID was not developed for PC's with 2 drives, it has been co-opted for this application.Never did me any harm or any good.
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