4kB Sector sized disks and the Seagate FreeAgent GoFlex

Hi everyone,

For some time, the Microsoft Block Level Backup engine has had difficulties backing up to 4kB sector sized disks. The VHD libraries that it uses rely on 512B sectors on the backup disk.

The short story: please avoid the Seagate FreeAgent GoFlex disks. A full explanation is below. We are also looking out for reports of other incompatible hardware.

The long story:

For many months I have been trying to find 4kB sector disks so we could produce a KB article of incompatible hardware. However it has not been that straightforward. I have learnt the following:

  • Most, if not all disks nowadays have physical 4kB sectors, BUT the on-disk controller emulates it as 512B sectors
  • Therefore, at the SATA interface, computers will see most (if not all) disks as having 512B sectors

So if I were to draw a diagram, it would be:

Physical disk platters [4kB sectors] <=  Controller [512B sector emulation ] <= SATA Interface – sees 512B sectors

  • I have been unsuccessful in finding a disk that actually looks like it has 4kB sectors.
  • In my travels, I have encountered only 2 devices that report 4kB sectors
    • A very early Samsung 2.5″ 640GB USB 2.0 hard drive, probably about 2 years ago. Unfortunately this drive died early and I discarded it before I could do proper testing on it.
      • Subsequent Samsung 2.5″ USB drives don’t suffer from this problem. We bought (this year) a 640GB drive that at the SATA interface had 512B sectors.
      • The actual hard drive itself doesn’t seem to suffer fro the problem. I plugged a 640GB drive into a SATA interface and it reported 512B sectors
    • The Seagate FreeAgent GoFlex interface (SATA -> USB 3.0) which is available for purchase now and I actually bought two last month when I was in Vegas.
      • If you plug a 3TB drive in there, it looks as if the drive has 4kB sectors
      • If you plug a 1TB drive in there, it looks as if the drive has 512B sectors!
      • The conversion from 512B to 4kB sectors is done in the SATA -> USB 3.0 controller itself, NOT in the drive. For example, I plugged in a Hitachi 3TB disk into the interface and got 4kB sectors. But when plugged straight into SATA, it looks like it has 512B sectors.
      • The reason why the controller does this is because:
        • Windows XP only supports MBR partition tables, not GPT
        • As such, it can only address a limited number of sectors, and with a 512B sector size, this equates to an addressable space of about 2.2TB
        • However, if you use 4kB sectors, this expands 8 fold!
        • So Seagate’s controller emulates 4kB sectors so that Windows XP can address the full 3TB disk with the MBR partition table
        • This emulation is not needed in Vista / 2008 / 7 / 2008 R2, BUT Seagate wanted to support XP so they did it anyway
        • The downside is that backups don’t work to the device on Vista / 2008 / 7 / 2008 R2

So a similar diagram is:

Physical disk platters [4kB sectors] <=  Controller [512B sector emulation ] <= SATA Interface <= SATA to USB Interface on GoFlex [4kB sector emulation] <= USB Interface sees 4kB sectors


  • Avoid the Seagate FreeAgent GoFlex hardware
    • It’s not the hard drive, but the interface, that causes the problem
  • Please be on the lookout for other incompatible hardware and post a reply to this blog article. Our resellers have asked us to start a website of backup hardware reviews, and that’s something I’ll look at doing in the coming months.

Thanks all, and I hope this helps everyone understand this problem better.




12 thoughts on “4kB Sector sized disks and the Seagate FreeAgent GoFlex”

  1. Thank you Neil for letting me know. I’ll buy one of these drives here in Australia and we can use it for testing.

    Just letting you know that we are working on a workaround for this issue (and have been for 6+ months) – we have designed it and I believe it should work great, but we’re having problems with the prototype at the moment. It’s probably about 6 months away from release, but we are working on it so this problem won’t be a “problem” forever.



  2. Hi Linus,
    We have had excellent results across a broad range of customers with the Samsung Story range of drives.


  3. I took this issue up with Microsoft Australia on twitter (@MSAU) and they recommended using Seagate Constellation SATA drives (3.5″) in Welland USB enclosures. Yes, they do work but are a lot more bulky than the 2.5″ USB drives. I had to turn to these as the Iomega Ego, Samsung S3, and Seagate GoFlex drives had all failed to work correctly.
    There is a Microsoft technet page IIRC that details which drives work and don’t work but I can’t seem to find it right now.

  4. Does this only apply to the GoFlex 2.5″ drives or the 3.5″ drives also? Because I have been successfully using the GoFlex Desk drives with the USB3.0 interface at two sites for over a year now.

    • Hi Ben,

      I think it happens when the drive size is over 2TB. As an experiment I put in a 500GB disk into the GoFlex 3.5″ connector and it came up with 512 byte sectors. But I connected a 3TB disk to the connector in the same way and it came up with 4kB sectors. That was using the GoFlex USB 3.0 dock.

      Hope this helps!


  5. The Microsoft KB can be found on <a href=”http://blogs.technet.com/b/filecab/archive/2011/04/26/using-4k-sector-and-advanced-format-drives-in-windows-hotfix-and-support-info-for-windows-server-2008-r2-and-windows-7.asp” title=”this technet article”>

  6. Hi Linus,
    We bought 12 Western Digital MyBook Essential 3TB external drives (3,5″) and cannot use them because of the same issue.
    Windows Server 8 is supposed to support 4k sektors with the new .VHDX standard but is still a long time away from release.
    A integrated solution in BA would be ideal! Keep up with the good work!

  7. Would this issue also means that Win7 will not recognize the partition if the drive is taken out of the USB3 controller and connected directly as internal drive (drive was formatted through the USB3 controller)? If so, it is terrible! Imagine one day if the USB3 controller dies, you have to find another controller in order to read the data off the drive!

  8. Exactly true. 3TB drives are completely incompatiable between naked SATA and that USB interface. It will not be readable if you switch the interface.


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