Why your new 2TB or 3TB drive will not work with Windows Backup

When Windows Vista and Server 2008 were released, Microsoft turned its back on tape backup. The built-in backup utility only backs up to hard drives. Windows 7 and Server 2008 R2 continue this policy. The recommended strategy for Small Business Server 2008 and 2011, for example, is to have a bunch of external USB drives and to use them in rotation.

Windows Server Backup, and its command-line version wbadmin, work well enough, but users with growing storage requirements have been buying larger external drives. That seems fine: external USB drives with 2TB and 3TB capacities are now commonplace. Except that they often run into problems when used with Windows Server Backup. You might see error 2155348010 or 0x8078002A, or “The request could not be performed because of an I/O device error”, or some other error.

The reason is that most of these large drives have a 4K sector size, rather than the older 512 byte sector size. You can get a patch for Windows 7 and Windows Server 2008 R2 that fixes most problems, but it does not fix the backup issue.

The further reason is that Windows Server Backup uses VHD virtual drives as its file format. The VHD format presumes the use of 512byte sectors, and the drivers that read and write data are optimised for this. You cannot create or mount VHDs on a disk with 4K sectors.

Microsoft has more information here and here.

Some drives have a firmware option to emulate 512byte sectors. These drives work, but with a performance penalty. Western Digital is one such, and you have a WD drive you may be in luck. See this post for details.

What is disappointing here is that these drives are mostly sold without any warning about these compatibility issues. The drive vendors will say that Microsoft should update its backup software; this is correct, but since the problem seems to be inherent to the VHD format it is not trivial to do so.

Another problem is that discovering whether or not the drive you are about to buy has a 4K sector size is not easy. Once purchased, you can find out by attaching the drive. opening an administrative command prompt, and running:

fsutil fsinfo ntfsinfo x:

where x is the drive letter of the target drive. This will show the sector size, and may even include the words “Not supported” in the output.

Windows Server 8 introduces the .VHDX format which both supports larger drives, and also fixes the issues with 4K sector sizes.


4 thoughts on “Why your new 2TB or 3TB drive will not work with Windows Backup”

  1. Have you tried running the backup executable from 2012 on a 2008 box to see if you can replace the system backup?

  2. The real kicker ,is that MS knew this was coming,and pretty much did a lousy job of even acknowledging the problem.

    I hang out over at Experts Exchange and have pointed folks to your website as reference for this issue,as MS has begun supporting this backup like an ugly stepchild.

    Good job and good references.

  3. This is too bad. Windows 7 is still very new (at least to me it is) and I prefer it over Windows 8. You would think if they can make this work in Windows 8, surely it wouldn’t be too difficult to also bring 4k support to Windows 7. I know of the workarounds but I still need my drive to work on XP. As such, I’m now looking for a different backup solution… :/

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