I have two sata hard drives configured as RAID1 that I am using as a data drive in my Win7 system. The OS is installed on a non-raid SSD drive.

After installing the OS and starting Win7 for the first time, the raid drive was not shown in My Computer. In Drive Management, the drive was listed like it should be, just without a drive mapping. I added one and the drive became listed and accessible in My Computer.

Since the drive was given a mapping after everything else was done auto, the drive now had a mapping later in the alphabet, so I rearranged the mappings so that this raid drive for data was listed right after my OS drive.

Now, whenever I restart, the drive loses its mapping. It is always listed in Disk Management, and I can always manually add a drive letter to it. However, with each reboot, this needs to be redone. I'd like to point my library folders (Pictures, Docs, Downloads, etc) to this drive instead of it being on C:\, so losing the mapping on every restart would be quite painful there.

In researching this, I was led to looking at mountvol and editing the registery. While this makes me nervous, the values don't quite seem to fit.

mountvol output: mountvol output

  • A: Floppy (don't even have one)
  • C: OS drive
  • E: Backup OS drive
  • F: CD/DVD drive
  • G/H/I/J: USB slots
  • Q: Backup Data drive

The first volume listed with no mount points I presume is my missing D:\ data drive. Note that this drive is currently mapped and showing in My Computer when I ran mountvol to get the output.

I've seen it suggested that \HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices can be edited to include the appropriate mountvol, but things don't seem to match up.

mounted volumes in registry (click for larger view)

So, there's a lot of extra stuff here, the first item listed being the volume without a mount point from the first image. There's also a K:\ drive which doesn't appear in the cmd output. Mapping my data drive to K:\ and restarting doesn't result in the drive being auto-mapped.

So, do I just need to add \DosDevices\D: with a value of 'c4 e9 85 18 00 00 10 00 00 00 00 00'? It is almost like each drive is listed at the top as a \??\Volume{blah-blah-blah} and then in the lower section as \DosDevices\, but not all of them match exactly like that.

I'd rather not just start dumping random values into the registry, so I'm hoping for more authoritative guidance then "hey, let's try this random thing!" (:

  • Do you have any data on the RAID array now? Would you be willing to destroy and then recreate the array? That way we could be sure it's not a fluke with a poorly built array or something like that. Random bugs unfortunately do happen once in a while. – Nick2253 Feb 8 '12 at 22:50
  • There's data, but nothing that can't easily be pulled from a source control repository again. – Rebecca Chernoff Feb 8 '12 at 23:16
  • Then I'd recommend recreating the array, and trying the two solutions in my answer. – Nick2253 Feb 8 '12 at 23:57

I have two possible solutions. Hopefully one will work:


This user has nearly the same problem you do, except it's with a single drive as opposed to your RAID array. This user was able to solve the problem by zeroing the entire volume, and then Windows was able to hold the assigned drive letter.


This user was unable to assign drive letters at all (which is slightly different then your problem). It was discovered that the issue for this user was a conflict with iTunes. By editing the registry, the user was able to assign drive letters once again.

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  • So, manually adding the drive letter when I reboot (which isn't often) finally annoyed me enough that I took the time to deal with this. I had to zero fill both of the drives. Not just the first and last, but the entire drives. I've rebooted several times since creating the array again and it's been mounting with the drive letter just fine! Thanks! (: – Rebecca Chernoff May 15 '12 at 1:43
  • The first link in your answer appears to be out-of-date; you may want to update the link or include the relevant information directly in the answer. – Sean Mickey Jan 22 '15 at 17:20
  • @SeanMickey The solution is already posted below (see zeroing the volume). You can also always check the Internet Archive if you want to see the thread directly. – Nick2253 Jan 22 '15 at 17:38

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