The 2TB Barrier

Pretty much all HDDs (and SSDs) are addressed using a scheme called Logical Block Addressing (LBA). The method is very, well, logical. Storage is addressed linearly, regardless of how the hardware itself is accessed. You start at LBA 0 and you go all the way up to the last address in your device. The number of LBAs you can address is a function of your hardware and the style of partition you’ve applied to your drive.

Master Boot Record partitioning is by far the most common on PCs today. LBA 0 contains the Master Boot Record (MBR) and your BIOS looks at the contents of LBA 0 to determine how and what to boot.

Now LBAs under MBR partitions are addressed using 32-bit values, the maximum of which is 2^32 or 4294967296. Each LBA on a hard drive corresponds to a 512-byte sector value (even on current 4K advance format drives, they still appear as 512-byte sector drives to the OS), so the largest partition you can have in a MBR partitioned drive is 4294967296 * 512-bytes or 2,199,023,255,552 bytes.

Hard drive manufacturers define 1TB as 1 trillion bytes. If we use that definition then the largest 32-bit MBR partition would be 2.199TB (2,199,023,255,552 bytes / 1,000,000,000,000). If we define 1TB as 1024^4 bytes (TiB) then the largest 32-bit MBR partition would be 2TiB (2,199,023,255,552 bytes / 1,099,511,627,776). Either way, with a 3TB drive there’s no way we’re getting a single 3TB partition using MBR.

In use on all Itanium and Intel based Macs (among other systems) is GPT (GUID Partition Table), and a feature of GPT is 64-bit LBA support.

With 64-bit LBAs the largest 512-byte sector drive we can address is 9.4ZB (Zettabytes - 10^21 or 2^70 bytes depending on if you’re counting in base 10 or 2). That’s an absurd amount of data.

GPT drives are supported as data drives in all x64 versions of Windows as well as Mac OS X and Linux. Below we have some screenshots of creating a GPT drive in Windows and OS X:

GPT Partition in Windows 7

GPT in Mac OS X

You’ll note that I said data and not boot drives. In order to boot to a GPT partition, you need hardware support. I just mentioned that your PC’s BIOS looks at LBA 0 for the MBR. Your BIOS does not support booting to GPT partitioned drives. GPT is however supported by systems that implement a newer BIOS alternative: Intel’s Extensible Firmware Interface (EFI).

Intel based Macs don’t use a BIOS and instead have an EFI which allows them to boot to GPT drives. Most PC motherboards however do not have EFI support, and those that do may have bugs associated with the implementation.

Case in point is Intel’s DX58SO, which just happens to be my default storage testbed. The good news is that Intel has deployed EFI on many of its motherboards. The bad news is the DX58SO (and potentially other models?) has some serious issues when you enable EFI.

The biggest problem I had was USB support dropping out completely when I enabled EFI on the Intel board. This is apparently a known issue and doesn’t affect all USB peripherals, but it prevented my keyboards and mice from working - which also meant that I couldn’t install Windows.

To make matters worse, even with EFI disabled I couldn’t get a 2TB partition created and installed to. The Windows 7 installer would simply complain that it couldn’t be installed to that drive.

There’s an odd bug with the DX58SO that lets you create a single 3TB partition with the SATA controller in Native IDE mode, and with that you can complete a full Windows 7 install. Note that in Native IDE mode you lose performance benefits like NCQ so it’s not ideal, but it’s the only way to get the drive with Windows installed on it.

Intel is aware of the bug and is working on a solution. Apparently the DP55KG board should work perfectly fine but that didn’t help me in this situation. Update: Intel has since sent me a beta BIOS that addresses a number of these issues, I'm playing with it right now but it didn't make the cut for use in this review. Thankfully it looks like Intel is aware of the problem and is actively working on a solution. I've also asked Raja to pay closer attention to EFI support in his motherboard reviews going forward.

My experience with the Intel board and installing Windows with this 3TB Seagate drive pinpoints why we don’t have an internal drive option for the 3TB Barracuda XT: the hardware isn’t ready for it yet. Consumers are used to buying a new hard drive and just sticking it in their system. With the requirements for EFI and GPT, we’re going to need a lot more effort from the motherboard manufacturers and clear messaging from the drive makers to avoid a lot of confusion in the marketplace.

Not Just Another Upgrade 3TB Internal Drive Performance - Nothing to Get Excited About Yet


View All Comments

  • zdzichu - Monday, August 23, 2010 - link

    In first performance table you switched results for SATA and USB3.0 of 3TB drive. Reply
  • oc3an - Monday, August 23, 2010 - link

    The maximum integer which can be represented with 32 bits is 4294967295 i.e. 2^32 - 1 which allows for 4294967296 values. The article is worded incorrectly. Reply
  • mino - Monday, August 23, 2010 - link

    " the largest partition you can have in a MBR partitioned drive is 4294967296 * 512-bytes or 2,199,023,255,552 bytes..."

    Are you sure that is an incorrect wording?
  • mino - Monday, August 23, 2010 - link

    BIOS does support booting from GPT.
    It is the Windows boot loader that cannot boot from GPT on BIOS systems.

    As a matter of fact I am writing this from Gigabyte 780G board running Ubuntu 10.04 on top of GPT(on top of LVM on top of MD on top of GPT).
  • yuhong - Monday, August 23, 2010 - link

    To be more precise, all that BIOS does is read the first sector of the drive, check for the signature at the end, and if it matches, then it jumps to the real mode x86 code at the beginning. It is actually partition scheme agnostic. Now some BIOSes are not quite partition scheme agnostic and will rely on the contents of the first sector being in the MBR format, luckily GPT support a protective MBR. Reply
  • baker269 - Monday, August 23, 2010 - link

    I would love to see what the Ethernet speeds are like. Not that great I would guess since it's not a true NAS, but still would be nice. Reply
  • mindless1 - Monday, August 23, 2010 - link

    ?? It doesn't have an ethernet interface does it? Speeds would be similar enough to any current-gen 7200 RPM drive already in a system on your LAN. Reply
  • baker269 - Tuesday, August 24, 2010 - link

    From the forth paragraph of the article.

    "The drives themselves are standard 3.5” hard drives in a plastic enclosure designed to mate with GoFlex Desk adapters that add USB 2.0, USB 3.0, FireWire 800 or Ethernet connectivity to the drive."

    It"s not as easy as just plugging in a hard drive with a RJ45 to a router, there needs to be some kind of CPU in between the two. NAS performance through Ethernet varies greatly.
  • derkurt - Monday, August 23, 2010 - link

    Is it such a big deal that Windows doesn't boot from GPT drives if the BIOS is not EFI-capable? Whoever spends 400+ USD on a drive probably just needs lots of storage space for plain data. It's unlikely that there is no fast boot drive present in any system this drive is plugged into. Actually, since the first expansive 3 TB drives are bought by enthusiasts, chances are that the customers are already using an SSD as a boot drive.

    That said, in a realistic setting for a performance workstation with Windows 7 x64 installed on a 80+ GB SSD, there won't be a problem. You can connect the drive to the internal SATA connector, partition it with GPT and start using it, while your BIOS doesn't need to know anything about EFI or GPT. The heat issues might also look better when using the drive internally.

    I don't understand why Seagate is holding back with selling the internal model. An estimated 95% of users will never even try to boot from it, and for the rest (who do want to boot from it but don't know about the 2+ TB issues), there could be a red warning note inside the box explaining the juicy details. After all, those who spend such an amount of money on a hard drive are not exactly the kind of people who have no clue about hard drives at all.
  • dryloch - Monday, August 23, 2010 - link

    One of Seagates biggest advantages has been that their external hard drives come with a 5 year warranty. Why would they go to a two year warranty on the most expensive drive they sell? If anything they should have at least gone with three years. If they don't even trust this drive then I sure won't. I'll be waiting for Western Digital to have their drive out. Reply

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