When I switched on today my second hard drive I had the following issue displayed
The disk is offline because it has a signature collision with another disk that is online
Running Diskpart as administrator proved that it was the issue
As you can see disk 2 and disk 4 both have the 00024A91 signature hence the collision.
Following the advise here, I changed the signature of the drive decreasing from 1 unit.
Than I brought back the disk online using Disk Management
And everything went back to normal
原文地址：http://www.laurentkempe.com/post/Windows-7-Disk-is-offline-because-it-has-a-signature-collision.aspx
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