I'm currently re-organising our disks on our VNX to distribute some load and I figured I take a closer look at our FAST Cache disk layout.

I initially came up with the following configuration...

Configuration 1 - The RAID1 is split over bus 0 and 1 and all the primary's on bus 1 (as per FAST Cache white paper)

naviseccli -h cache -fast -create -disks 1_0_0 0_1_0 1_0_1 0_1_1 1_0_2 0_1_2 1_0_3 0_1_3 -mode rw -rtype r1

I then realized with the nature of RAID1, when data is read, it's only read from the primary, however, when data is written, it's written to both primary and secondary. Thus the primary drive would be generating more traffic on a bus than a secondary would. So I came up with Configuration 2. According to http://support.emc.com/kb/82823 and I quote...

Existing best practices documentation for Enterprise Flash Drives (EFDs) states that for optimal performance, EFD RAID groups should be spread across enclosures or buses or both.

It doesn't mention if the primary and secondary drives should be evenly distributed as well.

Configuration 2 - The RAID is split over bus 0 and 1 and the primary's are split over bus 0 and 1

naviseccli -h cache -fast -create -disks 1_0_0 0_1_0 0_1_1 1_0_1 1_0_2 0_1_2 0_1_3 1_0_3 -mode rw -rtype r1

So my question is, does it matter where the primary and secondary drives are located on the bus's? Which configuration is preferred or does it not matter?