The purpose of any storage array is to serve and accept data as quickly as possible. The fastest way for an array to accept data is to do something called "full stripe write", as a "full stripe write" doesn't add any overhead to the write operation. A "full stripe write" means that the array is able to write a full stripe of data in a single operation. When using RAID5, all writes, unless they are "full stripe write", carry an overhead of 4 operations, meaning that for a single write, 4 IOPS have to happen.  Over the years, EMC has done extensive testing around how to maximise the occurrence of "full stripe writes" and has found that RAID5 4+1 and 8+1 are the RAID levels where "full stripe writes" happen the most often, partly because the number of data drives in the stripe is a power of 2. This doesn't mean that it won't happen if you use 5+1 or 6+1 or 7+1, but if you want the best performance, you will more than likely get it using 4+1 or 8+1.  I hope this helps, Bertrand.
Hi,   I know that EMC recommends using (4+1) or (8+1) configuration for RAID5 for Perfomance tire   I do understand the minimum recomendation (4+1) - in order to achive good perfomance and get more usable space  I do understand the maximum recomdation (8+1) - it's mainly due to availability risks  But why the configurations in between - (5+1), (6+1), (7+1)  is not recommended  Can anyone explain ?
VNX 5200 RAID5 configuration for storage pool