We all know that the number of actuators is important in Power for System i for performance.
But what if I changed for an existing external storage the 21 disks of 300 G Bytes 15 KRPM in Raid-10 by 4 SSD of 1,6 T Bytes in Raid-5? Well we could have the same capacity with a much faster response time!
Does it needs to be a Flash Storage? A V3700 with SSD is an alternative. The financial side is + 50K for disk but less expensive controllers on the Power side.