2011-02-23

Fix "This disk is offline because it has a signature collision with another disk"

I try to be diligent about backing up my data. After all, there are only tow types of computer users:

  1. Those who have lost data
  2. Those who will lose data

I’m occasionally not as systematic about it as I would like, but that’s changing.  I just finished my first complete data backup in some time -- all personal computers, network drives, and external USB drives. It turns out I have about 1.6 TB of data.

Phase 1 was to consolidate what I could to minimize duplication, and to back up everything to a single USB 2TB hard drive. It took about a week.

Phase 2 was began today.  That’s the phase where I copy everything on that 2TB USB HDD to another 2TB USB HDD and send it out of state.  This gives me off-site back up.  After all, all the backups in the world won’t do me any good if they are sitting in my apartment if disaster strikes.  Off site backup is an important part of any backup strategy.

The two 2TB drive that I’m using are identical models, and that’s where the problems came up.

I plugged the first one it, and it was fine.  I plugged the second one in, and it never came up in “My Computer.” Windows 7 did not appear to see it.  It tried rebooting, swapping the ports and still had the same problem.

So I dove deeper into the Windows setting. A word of caution here:  these tools give you the opportunity to really screw things up if you’re not careful.  Make sure you protect your data before getting into this.

A great tool to use when you have disk problems is the Disk Management tool. To access it in Windows 7, click the “Start” button, and type “Disk Management” in the search box.  When the option comes up, click “Create and format hard disk partitions.”

While the “My Computer” windows gives you access to the data on your drives, and to the drive letters (which may or may not reflect physical drives), this utility gives you access to the drives themselves. It tells you which physical drives are installed, and how those drives are divided up.

In my case, it showed both of my 2TB drives, but one was showing an error message:

“This disk is offline because it has a signature collision with another disk"

Windows identifies each drive based on a signature related to the physical components of the drive.  Because my two 2TB Seagate drive were both the same model, size, speed, and part number, they had the same signature.  Windows could not tell them apart.

The solution to that problem was to change the signature on one of the drives.  I found out how to do that at HowToHaven.com.  Their article on how to identify and change the drive signature is here.

The instructions are well written and easy to follow.  They do involve using the command line in Administrator Mode, and since you are messing with deep settings, it’s important to be careful.

Since one of my drives was blank, that’s the one I changed the signature on.  That way I didn’t risk any data loss if I screwed it up.

But the process worked fine.  I had no trouble.  I followed the instructions, exited the utilities, hooked up all the drives again, and everything appeared in “My Computer” just as it should.  And right now that computer is busily copying 1.6 TB of data from 1 USB drive to another.

The lesson here?

  • Back up your data
  • Learn to use diagnostic tool that come with Windows
  • Google error messages
  • Back up your data.

Those steps can help solve a heck of a lot of problems.

8 comments:

Bernie said...

After installing a second drive, Windows Explorer does not see the new drive because of Signature Collision.

Solution which worked for me: (type without these marks "")

Start >> Run >> type "Diskpart" and OK

This brings up the CMD window
1. Type "List Disk"
(This will show you which disks can by physically seen, offline and online)
2. Type "select disk X" (Where x is the number of the disk you want to make online)
3. Type "online disk" (This should bring you a message saying your disk is now online)
4. Type "Exit" This takes you back to windows and you should now see your disk through Windows Explorer.

erik said...

Bernie's solution helped me. However after I onlined the disk, Windows assigned it to the G: drive, which was reserved for another drive that was not connected at the time, so it didn't show up in Explorer yet.

To get it to show up, I followed Bernie's steps 1-3, then:
4. Type "List Volume"
5. Type "Select Volume X" where x is the letter that was assigned to your new disk
6. Type "Assign Letter=X" where X is an unused drive letter


After that, it showed up in Windows Explorer. I was also able to unplug the drive, change USB ports, and Windows recognized it when I plugged back in.

Anonymous said...


Do not try to "change signature"
Full backup before you made - to two hard disks

Important: WD warn that all of your information can go - without the ability to return
If during the attempt to create a signature change - there is a problem

The process will need to make every computer will need to connect the two drives - simultaneously
All these changes - more than once, greatly increase the risk that any business information
Lose

Work on disks with "signature collision" after the amendment of the "windows"
Not recommended, System Restore and other actions below may also cause future
Lose all your data

Anonymous said...

Just right click and tell it to go online. This worked for me - both externals finally appeared in my computer

ryan javier said...

this is very helpful.....thank you.....

ryan javier said...

this is very helpful...thank you.....

Country Boy said...

very helpful. Excellent. thank you very much.

Anonymous said...

I also just right clicked on the "offline" statement and chose go online and tada...worked perfectly