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raid5 or mirroring
- Thread starter JCROCCO
- Start date
spikespiegal
Golden Member
Not true.
Depending on your controller Raid 5 might cause a performance hit because of overhead processing parity logic.
I avoid RAID at all costs now - even on servers. Storage is cheap, and with RAID 1 a malfunction with my controller won't kill all the data on three drives. RAID 5 striping errors are catastrophic. They aren't with RAID 1.
Depending on your controller Raid 5 might cause a performance hit because of overhead processing parity logic.
I avoid RAID at all costs now - even on servers. Storage is cheap, and with RAID 1 a malfunction with my controller won't kill all the data on three drives. RAID 5 striping errors are catastrophic. They aren't with RAID 1.
Though I would disagree with this assessment...to each his own.
In answer to the OP: Either mirroring or Raid 5 will help protect against data loss if one hard drive fails. One thing that's very important is not to confuse a raid array with backups. A raid setup is simply for data redundancy. Nothing protects data like a good backup strategy!
Hard drives fail and there isn't much you can do to protect yourself from that but backups protect the data.
JCROCCO, you say:
"Not too concerned about down time."
RAID, fundemantally, is a technology that is used to increase performance and/or availability of a set of inexpensive disks. If you're comparing between RAID 5 and RAID 1 (mirroring), then you're pretty much looking at differences in RAID levels that exist to increase your availability. But if you aren't concerned about down time, you don't need RAID to (maybe) increase your availability. RAID adds complexity to the overall system. While RAID increases availability in the face of drive failures, it creates new things that could fail and new ways you as the sysadmin could accidentally screw things up.
I think you should instead focus on your backup solution.
FWIW, when it has to stay up and cost is not a big concern, I use RAID mirroring. When I need a more cost-effective solution is required, and/or a lot of storage, I use RAID 5 or 6.
Aside: There's a great Intel presentation floating around that shows you how RAID 5 doesn't scale to really big arrays so well - you need to use RAID 6. The key observation is that RAID 5 array rebuilds crank the drives really hard... which makes the odds pretty good that you're going to lose a drive during that process. Which increases your number of failed drives to two, which RAID 5 can't help you with. Obviously at some level, they're pushing RAID 6 because it's a cool-new-feature that sells stuff. But anyone around here who's managed a bunch of RAID 5 arrays will tell you that rebuilds are a stressful operation.
"Not too concerned about down time."
RAID, fundemantally, is a technology that is used to increase performance and/or availability of a set of inexpensive disks. If you're comparing between RAID 5 and RAID 1 (mirroring), then you're pretty much looking at differences in RAID levels that exist to increase your availability. But if you aren't concerned about down time, you don't need RAID to (maybe) increase your availability. RAID adds complexity to the overall system. While RAID increases availability in the face of drive failures, it creates new things that could fail and new ways you as the sysadmin could accidentally screw things up.
I think you should instead focus on your backup solution.
FWIW, when it has to stay up and cost is not a big concern, I use RAID mirroring. When I need a more cost-effective solution is required, and/or a lot of storage, I use RAID 5 or 6.
Aside: There's a great Intel presentation floating around that shows you how RAID 5 doesn't scale to really big arrays so well - you need to use RAID 6. The key observation is that RAID 5 array rebuilds crank the drives really hard... which makes the odds pretty good that you're going to lose a drive during that process. Which increases your number of failed drives to two, which RAID 5 can't help you with. Obviously at some level, they're pushing RAID 6 because it's a cool-new-feature that sells stuff. But anyone around here who's managed a bunch of RAID 5 arrays will tell you that rebuilds are a stressful operation.
Stressfull isn't the word for it! I agree with this statement above and use the same thought pattern. Just want to add, when you are buying SCSI drives for your server, using straight 1 doesn't work out when you want larger containers. 1+0 is just way to expensive on a large scale, and RAID 5 is a good mix of risk management and fault tolerance.
I also agree that RAID doesn't sound like it is for you, but a good back up plan.
RebateMonger
Elite Member
I like simplicity. So, where I can, I use RAID 1. It has the same performance as a single drive, can use inexpensive RAID controllers, and is the simplest system to manage and to recover.
Choosing between RAID 1 and striped arrays (RAID 5 or 6) is usually based upon two other factors:
1) Space efficiency - You lose 50% of your drive capacity with RAID 1. You lose 33% (or less) of your drive capacity with RAID 5, depending on how many drives are in the array. Unfortunately, as soon as you go to RAID 6, you start losing capacity again.
2) Expandability - You can keep expanding a RAID 5 or 6 array. That's the good news. The bad news is that you'll eventually end up with a slew of obsolete, low-capacity drives, as hard drive capaciities continue to expand. You won't be able to take advantage of the new drives in your RAID 5 (or 6) array, since the drive usage will be limited by the size of the original three drives in the array.
If you want to add capacity to a RAID 1 system, you just create another RAID 1 array with two more drives. You can buy newer, larger drives and take full advantage of them.
There's no right/wrong answer to all this. It really depends on the degree of complication that you are willing to live with, how you plan on expanding capacity in the future, and, sometimes, how much room you have for additional hard drives in your system.
Choosing between RAID 1 and striped arrays (RAID 5 or 6) is usually based upon two other factors:
1) Space efficiency - You lose 50% of your drive capacity with RAID 1. You lose 33% (or less) of your drive capacity with RAID 5, depending on how many drives are in the array. Unfortunately, as soon as you go to RAID 6, you start losing capacity again.
2) Expandability - You can keep expanding a RAID 5 or 6 array. That's the good news. The bad news is that you'll eventually end up with a slew of obsolete, low-capacity drives, as hard drive capaciities continue to expand. You won't be able to take advantage of the new drives in your RAID 5 (or 6) array, since the drive usage will be limited by the size of the original three drives in the array.
If you want to add capacity to a RAID 1 system, you just create another RAID 1 array with two more drives. You can buy newer, larger drives and take full advantage of them.
There's no right/wrong answer to all this. It really depends on the degree of complication that you are willing to live with, how you plan on expanding capacity in the future, and, sometimes, how much room you have for additional hard drives in your system.
RAID 1 (mirrored) is faster than RAID 5 for reading. So if most of your computer usage is *reading* data, such as playing games or loading applications or playing music/videos, then you might want to consider RAID 1.
Most RAID 1 controllers are smart enough to realize that the same data is mirrored to both drives, so when you read data from the drive, the controller pulls data from both drives at the same time, one piece from one drive while the other drive is pumping out the other piece. Almost twice as fast for read operations.
Most RAID 1 controllers are smart enough to realize that the same data is mirrored to both drives, so when you read data from the drive, the controller pulls data from both drives at the same time, one piece from one drive while the other drive is pumping out the other piece. Almost twice as fast for read operations.
RebateMonger
Elite Member
I tend to forget that you can do a RAID 1 array with more than two drives.
bigshooter
Platinum Member
Raid 5 is usually faster than Raid 1 for reading. Writing is slower because of parity calculations. Since Raid 5 is striped across more than just 2 disks you can read a piece of the file from each of the drives. Raid 1 is faster for writing since you are not calculating any parity.
Raid 10 is probably the best of both worlds for read and write performance, but you lose more space than you do with raid 5.
If downtime is not a concern, then drop the idea of RAID and use the second hard drive as a backup.
400gb -> 400gb online/live backup (pref in another machine) -> offline off site(or at least in a fire proof safe) backup like optical, tape or a rotataion of 400gb drives.
and once you have a backup plan in place then test recovering something. Nothing hurts more then needing to restore data and finding out your backup solution was faulty in some minor way.
RAID is purely for hardware redundancy and uptime.. it is not a good means of protecting your data from yourself and your users, only from hardware failure.
if you can afford the downtime of swapping out a drive, i'd rather have an imaged or ghosted drive ready to swap in.
QFT
If your not running a online transaction based application, and/or you business is not dependent on time sensitive data then just develop a robust backup plan, you'll get more use out of it, and be a hero when someone asks for the file they deleted/overwrote 3 months ago and you have it.
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