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I have successfully built and configured a Windows Home Server 2011 instance, where the system drive is 300g and there are two 1.5TB drives for storage. I intended the two large drives to be mirrored, and that is being done through WHS.

I have a 3TB external hard disk to be the server backup. But attempting to configure this always fails with a message that the greatest volume cannot exceed 2TB. Admittedly, the two mirrored drives account for 3TB but doing so would mean duplicate data. The backup system should see that as one 1.5TB drive, right?

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Is it not complaining that the destination volume is greater than 2TB? you're using a 3TB volume on a server that only supports 2TB. its still a volume wether its the backup source or the destination. –  user98471 Oct 20 '11 at 12:53
I thought of that, myself, and reconfigured the 3TB drive to be two volumes (each under 2TB). Made no difference. –  Michael Broschat Oct 20 '11 at 17:12

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It turns out that this is a common complaint. Answers from some technical folks agree with some Microsoft support documentation, and find the problem to be in the sector size of the drive one is attempting to use for backup. It is common for modern drives to move to a sector size of, say, 4K. Traditionally, sector size has been 512. Evidently, the backup utilities supplied by Microsoft still require that 512 sector size.

I think you can reformat such a drive to the extFAT format (which allows a sector size of 512--NTFS only allows 4k minimum). Unfortunately, my attempt to do this was foiled by a physical accident so I can't follow through. A 2TB drive also from Seagate works just fine (and confirms the 512 sector size), so I'll replace the now damaged 3TB with one of those.

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