The amount of space isn't so impressive, but the physical size and number of spindles.
I worked at one place that had 3 100tb disk arrays, each one was spread over 15 racks, giving 3gig a second throughput. (in 2007)
Now, 170 tbs, and a server fit in 5u. 60 disks give 2gigs(bytes) a second throughput. 2.5 racks gives you 5.5PBs and ~60gigabytes/second peak (25-8 sustained)
I worked at one place that had 3 100tb disk arrays, each one was spread over 15 racks, giving 3gig a second throughput. (in 2007)
Now, 170 tbs, and a server fit in 5u. 60 disks give 2gigs(bytes) a second throughput. 2.5 racks gives you 5.5PBs and ~60gigabytes/second peak (25-8 sustained)