Something strange with the EMC Symmetrix DMX4

There is something really strange in the numbers for the EMC Symmetrix DMX4. A colleague gave me this hint. Just look on the specification sheet. They state on page 2 that this system can house up to 2400 disk (albeit they restrict that in the footnote by writing that more than 1920 drives are just available on RPQ). But that´s not the point. Just look at the numbers at system capacity on page 3: They state on this whitepaper, that you can plug 1920 1 TB hard disks into the system. Okay …. let´s take the example for RAID 5 with 7+1. You could cut 240 of this RAIDs out of 1920 disks (1920/8). 240 multiplied with 7 Terabyte is 1680 Terabyte. But the maximum system capacity is stated by EMC with 585.91 Terabyte. WTF ?!?!? Where is the missing Petabyte? The first approx. 670 1 TB disks in your DMX4 gives you capacity, the other approx 1250 disks gives just heat dissipation and some nice blinking lights. I don´t really think, that there is an error in my calculations . Why? When you calculate this for 73 GB you get 122 Terabyte … almost the system capacity number stated on the specification sheet(you have to deduct some of the storage for internal usage, so it´s slightly less). I smell a architectural weakness here. Something like “640 Kilobyte is enough for everyone” decision … just on a larger scale ;)