Drive letter for EFI system partition?


  1. Posts : 42
    Win 10
       #1

    Drive letter for EFI system partition?


    In Macrium Reflect (free), a Dell Optiplex 3046 running 6.3.1835 on Win 10 64 Pro, returns a
    Cluster run error Cluster run short error 21
    when performing a backup that includes the EFI system partition. Macrium's suggested solution is to assign a drive letter to that partition. The EFI partition is required for a disk image.

    Before I assign a drive letter I'd like to understand what risks there are in the assignment.
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  2. NavyLCDR's Avatar
    Posts : 15,508
    Windows 10 Pro
       #2

    The only risk is that it will give the user and programs access to the EFI System Partition through the drive letter to make changes. I doubt that assigning a drive letter will fix the issue because we do backups all the time with no drive letter assigned to the EFI System Partition, but you can try, and just remove the drive letter after the backup is done.

    The good news is that it is extremely easy to rebuild the EFI System Partition.
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  3. Posts : 42
    Win 10
    Thread Starter
       #3

    I've finally gotten around to assigning drive letters - to no avail. chkdsk /r did not help.

    More detail:
    One of the partitions in the attempted image is display in red in Reflect:Drive letter for EFI system partition?-red_image.jpg

    There is nothing of note when viewing the disk in either Disk Management or diskpart.

    Still stuck. Is there a Macrium solution (so we can keep its installation) or should we go elsewhere?
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  4. Word Man's Avatar
    Posts : 1,562
    Windows 10 Pro
       #4

    The red coloration just means the partition is nearly full. Did you run chkdsk /r on every partition or only the EFI system partition? Or do you know the error is being thrown while imaging the EFI system partition rather than another?
    Last edited by Word Man; 26 Oct 2017 at 06:43. Reason: Typos
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  5. NavyLCDR's Avatar
    Posts : 15,508
    Windows 10 Pro
       #5

    It's pretty easy to rebuild the EFI System Partition. You just have delete the corrupt one. Create a primary partition where it used to be, format it as FAT32, assign it a drive letter. Run the command:

    bcdboot C:\Windows /s F: /f UEFI

    Make sure the drive letter in Red is the drive letter currently assigned to the Windows partition, and the orange drive letter is the letter assigned to the new EFI System partition.

    Then remove the drive letter from the EFI Partition and change the partition ID to: c12a7328-f81f-11d2-ba4b-00a0c93ec93b

    All of that can be done in an admin Command Prompt with diskpart commands (and exit diskpart to run bcdboot command).

    If you know what you are doing, takes less than 2 minutes to accomplish.
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  6. Posts : 42
    Win 10
    Thread Starter
       #6

    @Word Man:
    "Did you run chkdsk /r on every partition or only the EFI system partition? Or do you know the error is being thrown while imaging the EFI system partition rather than another?"

    I did not run chkdsk /r on every partition - I only ran it once, assuming that it ran on the entire disk. This sounds like in inaccurate assumption. Does chkdsk need to be run against every volume?

    @
    NavyLCDR:

    I may eventually get to rebuilding EFI once I learn where the error is. That appears to be the harder part right now.
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  7. Word Man's Avatar
    Posts : 1,562
    Windows 10 Pro
       #7

    geoB said:
    @Word Man:
    ...
    I did not run chkdsk /r on every partition - I only ran it once, assuming that it ran on the entire disk. This sounds like in inaccurate assumption. Does chkdsk need to be run against every volume?
    ...
    Well, you need to know which partition/drive the error occurred on to correct the error. I imagine chkdsk without a drive letter specification just runs on the system drive (c: in your case), it runs on a specified volume/partition not across an entire physical disk.

    I know that there is a thread at the Macrium support forum discussing the case where a cluster error occurred processing the EFI system partition (ESP) - was that perhaps your reference to "Macrium's suggested solution"?

    If nothing wrong with your ESP, chkdsk on that with a drive letter assigned would come up good and you would still be looking for the error.

    So, perhaps you need to run "chkdsk d: /r" (substitute the target drive letter for d: ) on each partition to find out which is bad - i.e., if the Macrium error message during the backup dialogue doesn't indicate which partition it is.
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  8. NavyLCDR's Avatar
    Posts : 15,508
    Windows 10 Pro
       #8

    Macrium Reflect will tell you which partition it is failing on. One thing you can do is to select the option to image one partition only. Start with your smallest partitions and work your way up in size. Then you know for sure which partition is failing.
    Last edited by NavyLCDR; 26 Oct 2017 at 14:44.
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  9. Posts : 42
    Win 10
    Thread Starter
       #9

    The procedure that enabled creating a system image:

    With diskpart, selected disk and volume containing the ESP partition. Assigned a drive letter with assign letter=E. Exited diskpart and opened an admin shell. Called chkdsk E: /r. Declined to dismount and accepted running chkdsk on restart. Restarted. Opened Reflect and successfully created a system image. Interestingly, the drive letter assignment disappeared.

    Thanks to Word Man & NavyLCDR my wife can now image and back up her system.
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