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Windows 7: Dual Boot – 1st OS partition not accessible from 2nd OS

09 Mar 2014   #1

Microsoft Windows 7 Home Premium 64-bit 7601 Multiprocessor Free Service Pack 1
Dual Boot – 1st OS partition not accessible from 2nd OS

The Problem: Dual boot Win7 – but OS on one HHD can’t access OS partition on 2nd HDD

Both HDD’s installed: When I boot to HDD2 with the cloned OS (it’s Disk 0 – C:) I see & can access both drives & all partitions). So I set up dual boot with EasyBCD. But I couldn’t get original OS - on HDD 1 - to boot; finally got it after more manipulations. However, HDD2 wasn’t seen – had to add a drive letter to “Backup Storage” partition on Drive 0.

But I can’t add/change a drive letter to the HDD2 - OS partition – W on Drive 0. How do I correct this?

Mgt Console - HDD2/Drive 0 - no problems

Mgt Console - HDD1/Drive 1 - can't change "W" letter

Mgt Console - HDD1/Drive 1 - attempt to change drive letter

attempt to access the files

Here’ how I got to this point:
A new SSD is coming tomorrow and I want to add it to an existing multi-HDD Dual Boot array (I have several existing setups). In the past, I’ve done clean installs to each HDD or SSD and used EasyBCD to setup the drive boot priority.

This time I want to clone an existing OS to the SSD and avoid the lengthy OS install/settings and tweaks. So I thought I’d do a dry run on a couple of existing systems before the SSD gets here.

Practice #1:
I used Clonezilla & everything worked out (had to run Startup Repair and use Partition Wizard & Paragon Rescue to assign drive letters & repaired boot mgr from command line) and got a successful boot then reinstalled the original HDD, booted then setup dual boot with EasyBCD.

Practice #2:
The second attempt on another PC – I ran into additional problems. After Startup Repair I was getting “autock program not found – skipping autocheck” which I eventually fixed by a regedit editing DosDevices\C: at startup/command line. I finally got the cloned OS to boot so I took out HDD 2 and installed the original HDD. I used Startup Repair & command line but still nothing – looked at disk structure and noticed Clonezilla had removed the drive letter from original HDD (which hadn’t happened in Practice #1). Fixed that then had the Autock not found – and fixed that. I got a good boot with the original HDD1 so I installed the HDD2 with cloned OS.

(PS - practically all my skills & tools/utilities have come from this forum - thanks!)

My System SpecsSystem Spec
09 Mar 2014   #2
Microsoft MVP


You may not change an OS drive letter. When you correctly install Win7 from boot media, it will always see itself as C when booted.

The letter of the other drive is inconsequential and only used to access data on it. Just accept whatever letter it gives and be done with it.

The best method with multiple HD's is to unplug the other HD when you install. Then choose which drive you want to boot via BIOS Boot order priority or the one-time BIOS Boot menu key. If you don't like this arrangement then add the other OS using EasyBCD. This leaves both HD OS's independently bootable. The way you've done it the W: drive Win7 is dependent upon C to boot.

W should also not be marked Active unless it's intended to boot an OS and it isn't now. If you wanted to make it independently bootable you would unplug the other HD and run Startup Repair - Run 3 Separate Times to write the boot files to the Active partition until it boots and holds the SYstem flag signifying it is booting Win7.

Does this answer your questions? If not ask back. Your description is a bit cloudy and too long to parse easily. But just keep asking questions until you are clear on what you need to do. We have answered these questions literally hundreds of thousands of times here.
My System SpecsSystem Spec
10 Mar 2014   #3

Microsoft Windows 7 Home Premium 64-bit 7601 Multiprocessor Free Service Pack 1

"The best method with multiple HD's is to unplug the other HD when you install."

I did this, that's why I can boot to either independently with the other unplugged. Here's the Mgt Console pics:

No. 1 HDD

No. 2 HDD

Changing the letter of the drive is not the key - I was using that as a symptom of another problem (I didn"t make myself clear).

When I boot into "New Win 7" I can access the files of "Ruds Win 7" in Explorer.

When I boot into "Ruds Win 7" I can't access the files of "New Win 7" in Explorer. For example, if I'm working in one OS and download an item to the desktop; I want to be able to retrieve it the other OS.


My System SpecsSystem Spec

10 Mar 2014   #4
Microsoft MVP


In the screenshot from your first post where both drives are attached it shows W booted, as signified by the Boot flag and correctly lettered C. However if you'll notice the new Win7 is still labeled System meaning it is booting both OS's in that screenshot.

It isn't until you unplug each HD in the latest screenshot that we see that Ruds Win7 drive become System. This is not normal. It's also likely the reason why you can't change it's drive letter. To resolve this try running Startup Repair on Rud's when it is plugged in alone to see if it finds anything to fix, then again when both are plugged in, to check over the Dual Boot configuration.

Next if necessary access EasyBCD in whichever OS you installed it to create the Dual Boot. On Edit OS tab delete the other OS listing to remove the Dual Boot menu, try booting your choice via the BIOS to see if this resolves the problem. You can always restore the Dual Boot using EasyBCD.

The inability to see the files on the other OS is anomalous so may or may not be resolved by these efforts. If not then try running Disk Check on both drives, if necessary from the System Recovery Options Command Line. Establish a Clean Boot and test both HD's from the Troubleshooting Steps for Windows 7. There are also other fixes to be found by googling the error text you posted, as there may be likewise working through repeat error messages in logs as shown in that tutorial.

If you'll report back results as you go, we may have other suggestions.
My System SpecsSystem Spec
11 Mar 2014   #5

Microsoft Windows 7 Home Premium 64-bit 7601 Multiprocessor Free Service Pack 1

Well after a bit more effort I was able to fix this problem. It was either the utility I used (or my handling of it) to change the drive letters at startup somehow locked the W partition.

I released all letters on both drives with Paragon Rescue Kit and re-assigned the C's and everything is back to normal.

Then I used Macrium to image the OS on my other PC and installed and set up the new SSD with the image. And made sure to clean up the registry drive letters before installing & it went without a hitch.
My System SpecsSystem Spec

 Dual Boot – 1st OS partition not accessible from 2nd OS

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