Three is min, 4x would be better. Best still would be to get the stacking cable so you can leverage the 10GbE. But with a single array not as critical. If you expand arrays and servers that's something to consider.
Sounds like you're off to a GREAT start!!
I think you're REALLY going to enjoy SANHQ. The latest version, 2.2, has a "Live information" feature so you can monitor a volume or member in real time. Plus there are some great reports and even a RAID evaluation tool that will show you based on past loads what different RAID types would do in your environment.
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