Is the EMC product with two storage controllers? The Promise item has only one, with no options to add more.
I would load up the EMC with Seagate Cheetah 15K.7 drives (they come in sizes up to 600GB http://www.seagate.com/www/en-us/products/servers/cheetah/cheetah_15k.7/) and really not worry about it. Each drive is rated at a sustained data rate of 171MB/sec. They are listed in the EMC tech spec's sheet (3.5" 600GB 15K RPM SAS drives). That would give you about 3.6TB of usable space (under RAID 10 of 12 drives)... How much space do you really need?
Since the Promise only has a single controller, I suspect that's one of the reasons it's almost half the price.
EMC does have a proven track record of quality products in the storage space. Especially when performance, and reliability, is necessary/critical.
I would also say to look at the EqualLogic solutions. I would go with SAS drives there too, in either one of the PS6000X/6000XV or PS6500X series arrays.
Both the EMC and EqualLogic arrays have much better expansion options compared to the Promise unit (another factor, I'm sure, in the lower price).
If you really do need high IOPs for the environment, then you'll need to spend the funds to get it. Don't expect the cheapest solution to perform to the same level as the big boys. See if you can get some customer contacts from both manufactures to get real world feedback on either product line.
VMware VCP4
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