How do I Defrag/Optimize a Windows 8.1 Volume which has no Drive Letter? Does it matter?


I have a Dell Inspiron Ultrabook running Windows 8.1 (64-bit). In File Explorer, I click on Drive C Properties -> Tools -> Optimize. There I see 4 drives listed as follows:

  • OS (C:) -- OK (0% fragmented)
  • PBR Image -- OK (0% fragmented)
  • WINRETOOLS -- OK (0% fragmented)
  • \\?\Volume{6e84d74b-fb3c-4a0e-9662-694d4192fb09}\ -- Needs optimization (94% fragmented)

If I select the "...{6e84d74b..." drive volume, and click the Optimize button to try to run Defrag on it, nothing happens except that an error appears in Event Viewer -> Windows Logs -> Application Log. The error that gets logged there is as follows:

Error, Event ID 257, Source: Defrag, The volume \\?\Volume{6e84d74b-fb3c-4a0e-9662-694d4192fb09}\ was not optimized because an error was encountered: The parameter is incorrect. (0x80070057)

Note that this system has two entries in Device Manager under Disk Drives as follows:

  • SSD PM830 mSATA (Disk 1, with 1 volume listed)
  • ST500LT012-9WS1 (Disk 0, with 5 volumes listed)

Unfortunately, I don't know how to tell if the "...{6e84d74b..." drive volume resides on the SSD (Disk 1) or the HDD (Disk 0). If there's a way to figure that out, I'd like to know.

So, I actually have several questions here:

  1. What is this drive volume used for; and does it really matter that it's fragmented?
  2. If it does matter, then how can I go about defragging it?
  3. In the logged error event, exactly which "parameter" is incorrect?
  4. How can I tell which physical drive this volume is located on?
asked on Super User Sep 19, 2015 by Tom-T • edited Sep 19, 2015 by Tom-T

1 Answer


1. What you see there is just an unmounted partition. Easier said, a partition without a drive letter, so we don't know what it's used for. Maybe it is a recovery partition.

2. Right click on your windows icon and open Command prompt (Admin). Type mountvol J: \\?\Volume{6e84d74b-fb3c-4a0e-9662-694d4192fb09}\. Only use J: if it isn't used already. This command will mount the partition and you will see it in the explorer. Now you can try to defrag again.

3. I don't really know. Maybe because it tries to access the partition through \\?\Volume{6e84d74b-fb3c-4a0e-9662-694d4192fb09}\ and not through a drive letter like J: and that is causing the command to fail

4. Open Disk Management after mounting the partition and you will see to which hard drive the partition belongs.

answered on Super User Sep 19, 2015 by schacker22 • edited Sep 19, 2015 by schacker22

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