We have a short whitepaper "White Paper: An Introduction to EMC CLARiiON CX4 Disk-Drive Spin Down Technology — Applied Technology" that could influence your decision, and if you do choose to enable it discusses how to manage it, explanation of the algorithm that decides what defines is "idle", best practices, etc:   From PowerLink, the breadcrumb trail is as follows:  Home > Support > Technical Documentation and Advisories > Hardware/Platforms Documentation > CLARiiON CX4 Series Systems > CLARiiON CX4-120 > White Papers   In summary, the main considerations with spin-down are:  1) Reliability due to spin-up/spin-down cycles There is a section: "Reliability" which discusses the testing EMC performed, and also the proactive measures that are performed by Navisphere/Unisphere to verify that a drive will, in fact, spin-up as noted in the "Ongoing processes that ensure reliability" section.  2) Inherent latency as the drive needs to first spin-up before being written from/to As noted, backup and archiving is a work-load profile that is a "natural fit"; for other applications keep this in mind.  There is, of course, compromises (power savings vs. latency).  3) Also, FLARE limits the number of drives that can spin-up simultaneously in the same enclosure (DAE) thus adding to the overall possible latency: a) Up to four at the same time b) Waits 12 seconds before spinning up the next set of disks   Finally note there are restrictions enforced by Navisphere/Unisphere (cannot use with layered applications and cannot be enabled on the first five system drives): [IMAGE]
I really like the option to be able to spin down the spindels that are unused to save power on the Clariion system but wanted to see what the caveat would be. I guess my question is why would someone not enable this option?  Thanks. 
Storage system power saving