The two choices you are considering - FAS2552 and FAS8020- are significantly different from one another. At a rough level, the 8020 is four times "bigger" than a 2552 in terms of compute (internal processor capability), memory, I/O connections, potential total storage, size of the storage units you can create (aggregates), etc. You can get all those from the NetApp Hardware Universe, which I'm guessing you've done.
Performance, like IOPS, is harder to pin down, because there are a lot of variables. You mention this is for SAN loads - iSCSI? FC? Got enough ports? Going to be all high performance disk or mixed performance/capacity? What's the I/O pattern? Going to go all out on cylinders (like a mass of 600GB disks for higher total I/O) or going to use fast but big (same capacity but 1.2TB performance disks - half total I/O potential for instance). Going to want some internal FlashCache for read acceleration - need the 8020. Going to want some SSD for read and write acceleration? Again you'll want the 8020 as the 2552 only supports the one disk loop. How much total capacity do you want? Going to replicate that data somewhere? Load going to get bigger anytime soon?
All of these items go into any generalization. If you have a good model of the workload desired of course your NetApp reps can model that workload into tools for recommendations on platform with a prediction of how much of the compute would be used at a given load level. But, that depends on you really knowing your I/O load - including read/write mix, block size patterns, latency target, etc.
All platform IOPs performance claims are suspect because of the variability involved. Within a given class of platform, for instance disk based SAN, bad design can make a supposedly "good" system go way slower than a "bad" system. Leverage your reps to help you make the best decisions. Ask your reps (vendor partner and/or NetApp direct) for the performance modeling outputs for potential solutions under consideration.
If a FAS2552 meets your current and projected needs, it's certainly a lot cheaper if you need just the one (or one HA pair). I'd expect that 4x2552 is cheaper than 2x8060 which might give you more options on how to place storage loads, so that also has to be taken into consideration, if you have more load than 2x2552 can handle but don't need what 2x8020 could provide.
Hope this helps you
Bob Greenwald
Lead Storage Engineer, Huron Legal
Huron Consulting Group
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