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On my work computer I have two USB hard drives that I use rarely (only for backups). They have a power save mode that sends them into sleep after a couple of minutes of them being idle. But whenever I open a context menu on a file, the drives are woken up (most likely caused by the "send to" handler). This causes a delay that gets really annoying really fast.

So I was wondering, is there a way to just unmount the drives and then remount them later on when I actually need them? I'm looking for a solution for Windows 7 (Ultimate if it makes a difference).

When I eject the drive, I can't find a way to get it back, other than unplugging and replugging it in.

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2 Answers 2

up vote 11 down vote accepted

Remove the drive letters using mountvol or diskmgmt.msc. Without a drive letter, they won't appear under Computer or Send To.

mountvol Q: /d

Reassign when needed, using the volume ID printed by mountvol:

mountvol Q: \\?\Volume{1be3da43-6602-11e0-b9e6-f11e1c50f5b5}\

You can also mount the volume on an empty folder (Unix style) using the same tools:

mkdir fs\backup-disk
mountvol fs\backup-disk \\?\Volume{1be3da43-6602-11e0-b9e6-f11e1c50f5b5}\

All these operations require Administrator privileges.

(In fact, you might even be able to directly use the volume ID in your backup scripts, without having to mount it anywhere. For example, \\?\Volume{1be3da43-6602-11e0-b9e6-f11e1c50f5b5}\projects instead of Q:\projects.)

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@OliverSalzburg: The volume GUID is tied to that specific volume, and persists after reboots. (It has to, in order for persistent drive letter assignments and filesystem mounts to work.) But unfortunately it's local to the machine. (As far as I know, Windows has no way to reference volumes by label or filesystem UUID yet.) –  grawity Jun 12 '11 at 8:39
@OliverSalzburg: Although if you browse the Object Manager using WinObj, you'll find more symlinks pointing to the same \Device\...: for example, to access my iPod I can use E:\Music or \\?\STORAGE#RemovableMedia#7&bec343e&0&RM#{53f5630a-b6bf-11d0-94f2-00a0c91efb8b}‌​\Music... But again, those appear to be variable between machines. –  grawity Jun 12 '11 at 8:50
Is this really the same as unmounting in UNIX? On a UNIX box, once the volume is umounted, it's safe to rip it out of the computer. (Maybe it'll make your SATA bus upset, if you don't have the appropriate hardware support for that, and you might need to reboot, but you won't lose any data.) If you can still access the disk as \\?\Volume{...}, doesn't that mean the filesystem is still available to the OS, and therefore might have unflushed data in write cache and so on? –  Glyph Feb 8 '13 at 6:22
@Glyph: UNIX is dead – better compare this to Linux or another modern operating system. On Linux, a single fs can be mounted on multiple places, usually using "bind mounts", and all of them must be unmounted to detach a filesystem. On Windows, you could also say that the OS has a few automatic mountpoints (\\?\Volume{…}), and the mountvol command manages additional mountpoints. So the filesystem remains attached as long as there is at least one mountpoint – even when you remove all user-facing mountpoints from mountvol's list, you still have the internal \\?\Volume{…} one. –  grawity Feb 8 '13 at 11:29
@DavidBalažic: /D only removes the drive letter (or path) assignment. Dismounting means detaching all such assignments, as well as closing the filesystem itself. Remember that Windows mounts all filesystems by default on the \\?\Volume{…} paths, and therefore regular mountvol usage only adds/removes additional ones (like mount --bind /x /y on Linux). –  grawity Nov 22 '13 at 16:11

The correct answer is using the /P parameter to mountvol (see the comments in the accepted answer to understand why /D is not enough) but that only applies to recent windows versions (NT kernel version 6 and up).

The devcon utility as described in this answer works across all NT versions

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