We currently have a cascade of two MSA50 arrays connected to a P600 controller. Is it possible to add a MSA60 array to the cascade? HP documentation states that MSA60 is compatible with P600.
From a P600 (or a P800 for that matter) you can only have two disk enclosures per external channel - i.e. a primary MSA then a secondary one daisy-chainedp600. That said you can mix MSAs, primary can be a 50, secondary can be a 60 or 70 etc. Obviously you won't be able to effectively create an array combining the disks from both a 50 and 60 due to the slight differences in disk sizes (2.5 vs 3.5 inch disks) but you'll be able to have two arrays.
edit - be careful with the SAS cables you use by the way, there's two connector types and it's easy to get the wrong ones :)