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I accidentally marked my external hard drive partition as active in disk management. I meant to change the drive letter but hit the wrong button. Whoops. What are the consequences of having done that and is it possible for me to undo it? Below is a screenshot of my drives. My internal laptop HDD has C: (Windows 7 OS) and D: (extra data partition). This is regarding my other disk: Disk 1 G:

enter image description here

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up vote 9 down vote accepted

The active partition is the one used when booting from that disk. This is why your system partition on your first disk is active. It doesn't affect anything else.

If you still want to remove it, open a command prompt with Administrator privileges and start diskpart.

Step by step instructions from here:

Type SELECT DISK n (with n being the number of the external disk)
Type SELECT PARTITION n (where n is the number of the active partition you wish to make inactive)
Type EXIT to exit DISKPART
Type EXIT again to exit the command prompt

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Exactly what I needed -- worked perfectly! – Mark Mar 5 '11 at 18:29

If you get a read-only error, do this first:

select disk X
attrib disk

You should see some results like below (my test disk was boot disk)

Current Read-only State : No
Read-only : No
Boot Disk : Yes
Pagefile Disk : Yes
Hibernation File Disk : No
Crashdump Disk : Yes
Clustered Disk : No

if your disk is set to ready only use the similar command for volume on your disk.

attrib disk clear readonly
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