Hello pdkilian,  Providing update here in addition to the Ask The Expert discussion:  I have contacted Engineering directly to provide information in response to your question:  EMC would recommend that, rather than moving more luns and filesystems onto a single 10+1 disk RAID5 group, that two 4+1 RAID5 groups be used. This gives better protection against a dual drive failure without sacrificing performance. I don't have hard performance numbers to post, but we expect the two 4+1 and the 10+1 configurations to deliver about the same performance. The 10+1 (plus one hotspare) will give you a little more available space but exposes more data to dual drive issues.  Kind Regards  Graeme
I noticed that in MR4, there is a new RAID configuration option of RAID 5 (10+1).    I currently have 10 SAS drives in my performance pool set up as RAID 5 (4+1) plus a hot spare and an unused drive for a total of 12 drives.  Because I am not a storage specialist, I am wondering if the new RAID configuration would make any appreciable difference in IOP's?  I think that by moving to the new RAID configuration, I would gain one drive, but I'm not sure how to figure out the performance difference of moving from two parity drives in my current setup to one in the new configuration.   Best Regards.
MR4 New RAID Configuration