Planning a RAID

If you are planning a new RAID, you need to get several factors right.

Protection against drive failures.

It is important that RAID is not a substitute for a backup. RAID can not save you from operator errors or fire, tornado. Anyway, certain RAID levels would keep you in business when one of the member disks stops working. here we speak about RAID1, RAID 10, RAID4, RAID 5, RAID 6, and exotics like RAID5E, RAID 5 EE, and RAID-DP. There is much speculation on RAID5 reliability supported by calculations concluding that high-capacity RAID5 is flawed. These calculations are based on vendor-specified Unrecoverable Error Rate values, which can be shown to be way off-base.

Capacity.

The size of the RAID limited by the maximum disk size you want to use, number of ports available on the RAID controller, and the capacity needed for redundancy . Should you want a simple calculation of the array capacity, have a look at free RAID Calculator.

Speed requirements.

From all the really redundant RAID levels, those using mirroring, namely RAID1 and RAID10 are the preferred on random write access. If the array is mostly used for reads (similar to a media library), or a write-once-read-never pattern (e.g. a backup storage), then RAID5, RAID6, and combinations of them are fine. Should you want fast random writes, choose RAID10. To quickly learn about speed, cost, and redundancy for different RAID types, look at the “RAID triangle“. Take into account that no RAID does in fact decrease random access time. For small random access times, try SSD.