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I have en external HD that I use with OS X. When I bought it, it was formatted for Windows (NTFS). I deleted the NTFS partition and created a new HFS+ partition. Then I copied 500 GB of material over.

Everything works fine when the external HD is directly connected to a Mac, but if I want to share the external HD by connecting it to a Time Capsule, I get an incorrect error message about the HD needing repair.

The problem is that the partition MAP is still in Windows format. For Time Capsule to recognize the disk, the partition map has to be in Guid Partition Table (GPT) format.

To do this, I have to delete the existing partition map. Will this also delete the underlying partition contents?

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Partition table formats are either MBR or GPT. There is no "Windows format." MBR is the older format which is still current an in use today, while GPT is the newer format that provides more flexibility and is where the industry is headed. – Randolf Richardson Mar 7 '11 at 11:35
Older versions of Windows (before Vista SP1 maybe?) will not detect GPT and work with it correctly and that's the reason why windows uses MBR. It's possible to have MBR and GPT coexist fine,if the drive has less than 4 partitions, but I can't be bothered to look it up at the moment and provide detailed explenation. – AndrejaKo Mar 7 '11 at 18:04

It's difficult to know for sure. Even if software promises not be destructive when changing the partition table, I still wouldn't take the chance without having a full backup of the drive first. Especially with a major operation such as change the partition table format, I'd worry that there's an even greater chance of data loss.

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To do this, I have to delete the existing partition map.
Untrue. One can convert from the MBR partition table scheme to the EFI partition table scheme non-destructively using appropriate tools.

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GUID is the new partition scheme and MBR is the old one

try to use this link

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