3 TB drives

Mac Pros can, but I read recently that 2.1TB was the limit for HFS+, but this article disagrees...

http://support.apple.com/kb/HT2422?viewlocale=en_US

Maximum number of volumes (all Mac OS X versions)

no limit
Maximum number of files (or files and folders) in a folder (all Mac OS X versions)

up to 2.1 billion (2)
Maximum volume size and file size (Mac OS X 10.0 - 10.1.5)

2 TB (1)
Maximum volume size and file size (Mac OS X 10.2 - 10.2.8)

8 TB (1)
Maximum volume size and file size (Mac OS X 10.3 - 10.3.9)

16 TB (1)
Maximum volume size and file size (Mac OS X 10.4 or later)

close to 8 EB (1,3)

I wouldn't trust an article written before 2.5TB drives existed, all theory, like the one from OS 7.5 as well.

2TB was mentioned back in OS 7.5.2 days:
http://support.apple.com/kb/TA27115

Hard to imagine WD and others selling any drive that does not work in systems today and we find support from 10.4.6 and later. One reason for Apple moving away from APM.

WD Support 2TB+

WD Advanced Format (you didn't say what drive so assume WD or similar issue).

Mac OS version 10.4 onwards (Tiger, Leopard and Snow Leopard) can use the GUID Partitioning Table scheme (GPT) which will align an Advanced Format drive correctly. Mac OS versions using Apple Partition Manager (APM) will not align partitions correctly and will not provide optimum performance.

New drives from WD are optimized for operation with... Mac OS X Tiger, Leopard, Snow Leopard.

http://www.wdc.com/en/products/products.aspx?id=120

To change partition format
http://support.apple.com/kb/TS1550

Apple Partition Map does have limitations.
http://developer.apple.com/technotes/tn2006/tn2166.html

Any Macintosh computer running Mac OS X 10.4 and later can mount GPT-partitioned disks.

Intel-based Macintosh computers can boot from GPT. By default, the internal hard disk is formatted as GPT.

IMPORTANT: While Intel-based Macintosh computers can boot from GPT and APM, Apple only supports booting Mac OS X on these machines from GPT. Apple's GUI tools, like the Installer, will prevent you installing Mac OS X for an Intel-based Mac on non-GPT disks.

with Mac OS X 10.4.6, PowerPC-based computers as well), Disk Utility has full support for GPT.

...
For big disks, we always create a 200 MB EFI system partition (ESP) (see ESP Explained) as the first partition on the disk. We also leave 128 MB of free space after each partition (not including the ESP).

From Microsoft some more up to date information about GPT and UEFI
http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx
http://support.microsoft.com/kb/302873

From Intel (UEFI and GPT support on Intel RAID)
http://www.intel.com/support/motherboards/server/sb/CS-031158.htm

Hitachi 3TB Deskstar 7K3000
http://macperformanceguide.com/Storage-Drive-Hitachi-7K3000-3TB.html