Performance depends heavily on the controller and what the array will be used for, but generally speaking, RAID 5 will provide superior performance to RAID 4 as most controllers can write the parity faster. I'm a big fan of RAID 6 if the controller supports it.
RAID 4 uses a type of parity that takes longer for most controllers to write and this is exacerbated by the fact that RAID 4 uses a dedicated parity disk instead of distributed parity, as seen in RAID 5. On an array that gets hammered on a regular basis, you will always be waiting on the parity drive. This can be offset if you have a controller that can use a separate high speed RAID array as the parity drive, but you're still faced with higher controller load for the parity writes.
In closing, no one uses RAID 4 any more. Seriously.
Ah... RAID. Just when you think you have it understood, Icrontic is here to pile on another lifetime of education. So much to learn so little life to live. Thanks for stopping in, Dunul. Stick around and you'll find us a great bunch.
Mas0n, good info... how about info on RAID 6 over RAID 5 or even RAID 1+0/0+1.
I prefer RAID 6 over RAID 5 or even RAID 5 with a hot spare because it reduces the risk of data loss in the event that you have 2 simultaneous drive failures or a second drive failure before you have replaced the original failed disk or before the array has finished rebuilding to the hot spare. I mainly feel this way because it has happened to me. Had good backups, so no real problems, just lost time rebuilding the array and restoring from tape.
The catch is obviously that it's more expensive to implement as RAID 6 requires an additional disk and typically a more expensive controller. Whether the additional cost is worthwhile is IMO determined by the amount of data to be stored and the level of activity expected of the array as these factors will determine the length of time required to rebuild the array in the event of a drive failure. In the situation I referenced above, there was a second drive failure while the array was still rebuilding to the hot spare. This was 22 hours after the initial failure. I now have this client on a RAID 6 array.
I can't really speak much to 0+1/1+0 other than hard facts as I have no personal experience with them. The controllers are typically more expensive and RAID 5 or RAID 6 work well for the size businesses I support.
I run RAID 1+0 in my desktop at home. Since I'm using a software RAID controller, not a true hardware controller, I end up getting better performance than I would running RAID 5 on the same hardware. Of course if you are using a true hardware RAID controller you are better off going with 5 or 6.
Comments
What will the array be used for?
I just thought in general who has the better performance...
But I still don't understand why does RAID 5 will provide superior performance?
In closing, no one uses RAID 4 any more. Seriously.
Thanks!
Mas0n, good info... how about info on RAID 6 over RAID 5 or even RAID 1+0/0+1.
The catch is obviously that it's more expensive to implement as RAID 6 requires an additional disk and typically a more expensive controller. Whether the additional cost is worthwhile is IMO determined by the amount of data to be stored and the level of activity expected of the array as these factors will determine the length of time required to rebuild the array in the event of a drive failure. In the situation I referenced above, there was a second drive failure while the array was still rebuilding to the hot spare. This was 22 hours after the initial failure. I now have this client on a RAID 6 array.
I can't really speak much to 0+1/1+0 other than hard facts as I have no personal experience with them. The controllers are typically more expensive and RAID 5 or RAID 6 work well for the size businesses I support.