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?

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.