Will a SATA III Hard Drive work on a Mac Pro 2,1 (2008)

It may, but I would not take the risk unless the vendor has a good return policy. That model supports 1.5 or 3.0 Gb/s SATA drives. Some 6.0 Gb/s SATA drives will operate on the lower speed bus while some may not. You must look at the mfgr.'s specifications to find out for sure.

Typically WD Caviar models will work in Mac Pros.

It works perfectly fine!!!!

There is no issue with it or any WD SATA III on SATA II. HUGE number of users even with more current systems use SATA 2 for data and don't have SATA 3 ports.

SAS is another matter. Require something like ATTO SAS/SATA RAID controllers.

Sonnet has a PCIe SATA 6G card but may not work properly in pre-2008 but is used to mount one or two SSDs for 500-900MB/sec.

Apple Pro RAID card is not compatible with 3TB drives and never will be it now seems. It also lacks any real performance and is destined where RAID 5 is a must.

SSDs are a more interesting matter in choice and support... but not traditional platter type drives.

I use SSD for system now 100% on multiple systems, 10K WD VR ($200 for 1TB / 180MB/sec and variety of WD blacks and Green.

2008 has some interesting stuff, PCIe mix and support and booting, but more choices in GPU. Runs best with all 8 DIMM slots filled. Was the first to have UEFI to support 64-bit kernel but does not support industry standard enough to support Windows 8 UEFI.

Storage market would be a total mess like it was back in 2004 when SATA 1.0 moved to 2.0 and lots of problems. SATA 1.0 in early G5 was just PATA with an SATA interface chip slapped on and not "native" SATA. THAT is where the "will the IBM Hitachi or Seagate or Maxtor" really did require research. Not with Mac Pro line 2006 and on.

Yes, SATA 3 drives will work.

I have a late 2007 Mac Pro upgraded to early 2008 2,1 status via a processor upgrade.

I'm currently running OS 10.7.5, with the original graphics card.

I've recently installed a 1Tb Seagate Barracuda drive, a SATA 3 drive, as my primary hard drive. Runs great, and since it replaced a SATA 1 drive, the speed improvement was very noticeable despite only connecting at SATA 2 speed. I think the extra headroom provided, plus the 64 Mb cache helped out too.

I then installed a similar Seagate drive, only in 2 Tb size, as the Time Machine drive. It's running fine as well, replacing a 320 Gb SATA 1 drive.

Everything is reported correctly in About This Mac.

Considering a SATA 3 Seagate 1 Tb drive can be purchased for less than $80.00, it's a pretty cost effective upgrade.

the biggest boost I got was adding / replacing an older 2010 SSD with the Samsung 840 and now system response is phenominal Even though it is only on SATA2 also and 'only' gets 260MB/sec in tests I did.

other changes: photo library of 100K is on its own SSD (on Sonnet Tempo SSD card) and iPhoto Library is on a 10K WD VR drive - reading from A and writing to B made a real difference. All my media and data is on 10K drive otherwise. So the system while it does have my ~/Library does not have anything else, meaning only 30GB out of 120GB is used.

The WD 10K now out (250, 500GB) are close to 175MB/sec in reads and writes and none of the possible issues with SSDs, TRIM. So you don't get quite the same IOPS but you get 2x for same $100 or $150.

2,1 is Mac Pro and cannot use Harpertown 5400's, only 53xx and would still only be able to use EFI32 (and no update from Apple beyond Lion).

The WD RED 3TB drive $118 and excellent for backup, NAS and RAIDs.

Apparently there are ways to install OS 10.8 if you want it. You will have to upgrade your graphics card, a HD 5770 will work and will run on a 2,1.

http://www.jabbawok.net/?p=47

I think this is the same method as above, or similar.

http://forums.macrumors.com/showthread.php?t=1550560

A video:

http://youtu.be/FPL5nko7Lz8

I haven't done this yet, I'm using 10.8 on my MacBook Pro Retina and I'm not particularly happy with it.

Although it is possible to install 10.8 using that and similar methods, it is not simple enough for "the rest of us". You need to be knowledgeable enough that if you have any problems, you can solve them yourself, since there is no one to provide support.

In addition, it uses some precious RAM memory, which also makes it less attractive.