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I've started using TrueCrypt to encrypt a partition on an external USB hard drive. I've opted for using a raw partition as opposed to a file container.

But here's the annoyance. Whenever I connect this drive to a computer running Vista or Windows 7, I get the message popup "You need to format the disk in drive J: before you can use it".

The default option is "Format disk", and I'm afraid one of these days I'll accidentally trigger it.

Is there any way to disable this message?

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Note there are two great answers here: The answer by Snark is great if you only want to solve to problem for one host computer and/or have added the truecrypted partition as a Favorite on any computer. The answer by SylikC solves the problem even for computers who haven't seen your USB drive before, but it (kind of) breaks adding that USB drive to TrueCrypt Favorites. – Jonas Heidelberg Aug 30 '11 at 15:02
I'm having the same problem with W7 wanting to format a BTRFS partition on my Android whenever I plug it in to charge... Windows = data loss by design – Mark K Cowan Aug 13 '14 at 12:56
up vote 34 down vote accepted

Try to go to the Control Panel - Administrative Tools - Computer Management. In the Disk Management part, remove the drive letter for the raw partition.

It should prevent Win7 from asking you to format the partition, while letting you mount the partition in TrueCrypt.

If it doesn't work, you could try this suggestion, which is to use Autokey to automatically dismiss the messagebox when it appears.

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+1 that does work, i'm using the same trick for my 'truecryped' sticks – Molly7244 Oct 1 '09 at 12:42
I believe the OP is looking for a solution that will work on any computer. Software installation is not then an option. – harrymc Oct 1 '09 at 13:10
Thanks! That did the trick. – Joe Attardi Oct 1 '09 at 15:07
A quicker way to open "Disk Management" is to Press Ctrl+R and type "diskmgmt.msc" :-) – Jonas Heidelberg Aug 30 '11 at 14:29
@msorens: no it won't; Windows identifies the USB hard drive through an ID written to its boot sector, so it will only ignore the partition from that specific hard drive. – Jonas Heidelberg Jan 10 '12 at 20:56

I have finally found a solution. I've tested this on Windows XP and Windows 7.

When you create a raw partition with TrueCrypt, it specifies it as partition type 0x06. This is a FAT partition, and Windows will always try to mount it.

Using a utility such as Beeblebrox (or your favorite RAW partition editor), change it to something else. I chose 0x64 which (based on the partition lists available) is a "PC-ARMOUR encrypted partition".

After changing it and then unplugging and replugging your device (power cycle), Windows will treat this partition as foreign and will not attempt to mount it. I will test it on Linux later, but I believe that'll prevent Linux from mounting it as well.

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Beeblebrox seems a bit outdated (last update of the Windows version in 2002) and I couldn't get it to run under Win7x64; under Linux you can change the partition type with fdisk (t option); in Windows 7 the build-in diskpart can do it with set id=64. – Jonas Heidelberg Aug 30 '11 at 14:19
This solution will solve the problem for that disk no matter what computer you connect it to, which is great :-). – Jonas Heidelberg Aug 30 '11 at 14:23
Only ceveat is that afterwards TrueCrypt doesn't recognize the volume as a favorite any more (if it was one). You can add it again but you can't give it a label, with the result that it is only recognized when its name of the form \Device\Harddisk5\Partition3 does not change. I.e. adding a different USB stick to your system before plugging in the TrueCrypted one makes the Favorite not work :-( – Jonas Heidelberg Aug 30 '11 at 14:24
I have tried working around the caveat using different partition types, in particular 0x27 and 0xc7, but it seems that either you get the format warning (when Windows thinks it should be able to read the partition and considers it a volume), or you can't assign a Label in TrueCrypt (when Windows ignores the partition). – Jonas Heidelberg Aug 30 '11 at 14:27
The commands for diskpart are: list disk / select disk # / list partition / select partition # / set id=64 / exit – mhenry1384 Oct 4 '11 at 1:09

I use a program called USB Safely Remove, which knows about TrueCrypt and can be configured to automatically pop up the TrueCrypt password dialog when certain USB drives are inserted. It also allows you to unmount the TrueCrypt drive and safely remove the USB drive with a single click.

It's a commercial product (with a free trial), but they are currently giving away some free licenses, if you're quick. It's legit -- I got my license in their last giveaway.

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The simplest and safest solution would be to simply format the usb disk and recreate the TrueCrypt virtual encrypted disk as the only file on the disk.

For completeness only : I note the need to first save all existing data within the TrueCrypt disk.

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I tried this: My portable HDD was NTFS-formatted and blank.

  • Encrypted it mounted
  • Added data
  • Unmounted it, re-connected and had this Windows message "you need to format…"
  • I unassigned the drive letter in disk management to the encrypted USB drive

That did the trick – no more pesky messages for me. I connect the drive and invoke TrueCrypt, select the portable HDD, click mount and provide the password. Voilà: The volume is mounted.

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