The limitation is 2TB for PHYSICAL disks. There is no 2TB limitation on VIRTUAL disks. 4.5TB is simply the total of "supported" (tested/validated) hard drive sizes multiplied by the maximum number of drives supported in the 2950. To find the maximum for your 2950, multiply the number of drive bays by 2TB to find your maximum. If you have an 8-bay 2950, then it is 16TB in RAID 0, but don't use RAID 0 - you are likely looking at a RAID 10 for reliability / performance, giving you 8TB of space ... 6TB if you have a 6-bay 2950.
I note the Hardware specs of the Poweredge 2950 suggests maximum of 4.5tb storage. My current server has 136GB drive in RAID and 4 x1tb(4gb) in RAID Is there a capability to increase HDD in excess of 4.5Tb?
Poweredge 2950 storage