Basil -

I would be very careful with choosing in this case.  FlexPool may be marginally more expensive but seeing as how the 8020 only has two PCIe slots adding a FlashCache module will severely limit your expansion options.  If that other slot is occupied by another 10GbE card you'll be limited to one SAS stack (10 shelves).  Furthermore, per best practices, mixing SAS/SATA drive types on the same stack is not encouraged (although it can be done), so you're essentially limiting yourself to one drive type.  On the other hand, if the other slot is occupied by a SAS card then you're limiting your connectivity options.  If you're running CDOT you're already going to be giving up two 10GbE onboard ports for the cluster interconnect so effectively you have two 10GbE/FC ports per controller.  If in the future you decided you wanted to add a tape drive (FC) or more 10GbE ports you'd be out of luck.  

Regarding performance, PCS doesn't really differentiate, and to be honest for most real world situations I've seen it's a wash.  The ability to have write caching via FlashPool is very helpful for random overwrite workloads.  'wafl awa' can help you determine the impact adding cache of either kind will have on writes/reads and how much optimally you would need.  It is important to run it at a peak time to see what the recommendations are, as running it during a relatively low activity period won't give much useful information. 

Anthony Bar
650.207.5368

On Jul 3, 2015, at 10:03 AM, Basil <basilberntsen@gmail.com> wrote: