You should have no problem. I think the max hard drives supported right now are 64. The size of the drives doesn't matter.

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@sunbound - Brandon is right, and theoretically 6 TB would work. Keep in mind, however, that you'd be potentially trying to move a ton of data through that little box, and the performance would likely not be optimal. I have a device here with 2 TB drives attached, and it works just fine, although initial setup (scanning drives, parsing metadata, generating thumbnails and video transcodes, etc) took a very long time - over a week, I believe.