ReadyNas 3200 OS6 Maximum Storage on Drive bays 1 through 4

Yes, you can install 10TB drives with no problem.

Since the 4200V2 uses a motherboard that is similar to the 3200/4200V1 but has an LSI 2008 based SAS controller to handle drive bays 5-12 instead of a Broadcom 1068E, I have wondered if it is possible to install an LSI 2008 based card in a 3200 or 4200V1, turn off the Broadcom controller, and see if the NAS will then use the LSI just like it would on a 4200V2, so those drives could also exceed 2TB.  The OS has to have a driver for the LSI to work with the 4200V2.  The LSI controller would likely need to be in "IT mode" (non-RAID) since te ReadyNAS needs to see individual drives to create its software RAID.

You'd need a couple CBL-0288L-01 SFF to SCSI cables, too.

Before you decide to get even more clever and replace the whole motherboard with the generic X8SI6 the 4200V2 is based on, it doesn't work.  I tried to see if one could be used as a replacement part on a 4200V2, and it didn't boot the OS.  I assume the OS looks at something in the BIOS to see it's a Netgear OEM version of the board.