Hard drive size limit in Mac Pro Early 2008?

Any SATA desktop 3.5" drive you can buy today will work fine in your Mac Pro 65lb tower. Install as many of whatever size you please. You can install 4 @ 4TB drives if you choose to. (And up to two more if you really, really want to.)

The only restriction is if you are using the Mac Pro RAID card, it can only access the first 2.2TB of each drive.

Apple only recommends what they test, and generally only tests what they sell. So if you look only to them for giudance, they will be way too conservative.

If you choose to install 2.5" laptop drives or SSDs, mounting them on the standard sleds is difficult. The left side of each drive (as mounted on the Mac Pro sled) must line up with the left side of the sled to allow the connectors to mate. In that position, only one of the screw holes will line up, and they require a different screw (3mm Optical drive mounting).

@Grant, that is not what I have found. I have an early 2008 Mac Pro/Mavericks and when I installed Western Digital 3 TB drives they are incorrectly reported in Disk Utility as ~870 GB. However, I have not had any trouble with 2 TB drives from Hitachi, Toshiba, Seagate or Western Digital.

2 TB appears to be the limit per drive. That said, you can install more than one drive of the same size and use Disk Utility to combine them as either striped RAID or concatenated disks to create a larger logical volume, e.g. 4 TB or 6 TB.

Also, I've discovered that the Mac does recognize the full 3 TB space of the WD drives if I install them in an external drive housing and connect them with a USB cable. Unfortunately, the speed of the USB 2.0 port is a poor choice for a backup solution. I determined that backing up 6.4 TB of data with Time Machine takes an estimated 31 days. If you take the path of installing external disks, then you may want to purchase a USB 3.0 adapter card. The only product that I know currently advertises Mavericks compatibility is the Sonnet Allegro.

Highpoint Technologies makes some cards that are popular, but they don't advertise that their products work with Mavericks yet. There is another thread where the issues with the Highpoint cards are discussed.

In t he YEAR since Grant posted, bugs were introduced into 10.8.4 and above that interfere with formatting drives larger t han 2.2TB. (It was to help iMacs with 3TB Fusion drives and with Boot Camping Windows). Very disconcerting that it is a) known for months and months and b) remains even as Mavericks is a whole new foundation and has a lot better software RAID features.

Also, there have always been people with trouble - but not all - with WD Green 3TB drives.

It is not a limit to GUID or EFI or to the SATA II controller.

Once you return t he 3TB drive from its place in a USB case or dock it will still be 3TB and work just fine.

I did pick up Sonnet USB3 PCIe 2-port card. It does not support hubs or smart devices like the ones I use on Windows. I would assume in time CalDigit would update their PCIe offerings.

Are you running 10.8.4 or 10.8.5?

There is a known bug in those versions that precludes correct formatting of drives over 2.2TB as INTERNAL drives.

Apple has suggested a work around: If you initialize those drives in an External enclosure, then move them to an Internal drive bay, they will operate correctly. [Just don't re-Initialize them internally.]

They also said that the bug appears to have been introduced when making modifications to support large Windows drives (so Windows drives over 2.2TB may work fine!)

EDIT: While I was composing, The hatter has provided some of the same information and additional insight. My post was not intended to dimish anything he says -- it was not there when I started writing.

Here is the manual page for a Mac Pro early 2008.

Installing Internal Storage Devices

Your Mac Pro has room for six internal drives: two optical drives and four hard disk

drives. In most configurations, a single hard disk drive occupies the first hard drive bay

and an optical drive is located in the top optical drive bay.

You can add up to three additional Serial ATA (SATA) hard disk drives to the empty hard

drive bays or up to four Serial Attached SCSI (SAS) drives. The drives must meet these

specifications:

• Type: SAS or SATA 3 Gb/s
• Width: 3.9 inches (102 mm)
• Depth: 5.7 inches (147 mm)
• Height: 1.0 inch

Important: To install SAS drives in your Mac Pro, you must also install the optional

Mac Pro RAID Card.

For more information about requirements or devices supported, visit an Apple

Authorized Reseller, the Apple Store at www.apple.com/store, or the Mac Pro Support

site at www.apple.com/support/macpro.

Installing SAS or SATA 3 Gb/s Hard Disk Drives

Your Mac Pro can accommodate up to four internal 1-inch-high SATA or SAS 3 Gb/s

hard disk drives in the hard drive bays. If your Mac Pro comes with a single drive

installed, it’s in the first bay. You can install drives in the second, third, and fourth hard

drive bays.

My own experience with backups is miserable:

Initially, I used a 1 TB backup disk in an Airport Extreme.

That disk only lasted 18 months.

I bought a second Airport Extreme recently and that internal disk has failed in only a month !

I have had nothing but disappointments installing external hard drives (2 and 4 TB).

I used the G-Drives and and a non-name drive holder and firewire 800 connections

The check out (I always check them with Disk Utility and TechTool) for read/write or h/w errors.

All looked good. I ran Time Machine to back-up a 500 MB and a 200 MB on a secondary 1 TB disk. (700 MB backup)

Each one ran about a week and then the disk drive failed.

On the 4 TB, I was able to erase it and reformat it, but it failed again in two days time.

So, I'm determined to back-up to an internal disk and I'm thinking about 2 TB WD because it's a bit faster (the external drives were using 5400 rpm seagate drives).

I plan to use the Mac Pro as a backup device, once I replace it.