How do I disable "you need to format this disk" message in Windows Vista/7?

"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."

"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."

"I want to re-confirm the answer that SylikC has given. You don't want to screw with your system, you want to indicate on the partition that it should not try mounting it. But there are 2 parts to this as I have found out.

First you do as SylikC says using diskpart set id=64 or choose from a wide range of partition types. But if you had previously assigned a drive letter to the partition, Windows 10 will still give you a ""Format this Disk"" dialog. To prevent that, you need to remove the drive letter assignment on the disk too.

To do that, before you set the partition type do

list volume
select volume <your volume with the drive letter>
remove letter=<your drive letter you want to remove>
set id=<now set the partition type>
...

If you had changed the partition type already, you have to first bring it back again to

set id=6
list volumes
select volume <your volume with the drive letter>
remove letter=<your drive letter you want to remove>
set id=64

And that is it. Next time you pop in that USB drive, no more warning comes up. And I had no problems mounting a TrueCrypt drive."
"I want to re-confirm the answer that SylikC has given. You don't want to screw with your system, you want to indicate on the partition that it should not try mounting it. But there are 2 parts to this as I have found out.

First you do as SylikC says using diskpart set id=64 or choose from a wide range of partition types. But if you had previously assigned a drive letter to the partition, Windows 10 will still give you a ""Format this Disk"" dialog. To prevent that, you need to remove the drive letter assignment on the disk too.

To do that, before you set the partition type do

list volume
select volume <your volume with the drive letter>
remove letter=<your drive letter you want to remove>
set id=<now set the partition type>
...

If you had changed the partition type already, you have to first bring it back again to

set id=6
list volumes
select volume <your volume with the drive letter>
remove letter=<your drive letter you want to remove>
set id=64

And that is it. Next time you pop in that USB drive, no more warning comes up. And I had no problems mounting a TrueCrypt drive."

"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."

"I managed to achieve it by creating the drive as a GPT and then using diskpart to modify the partition GPT ATTRIBUTES...

list disk
select disk # <- your disk number here
list partition
select partition # <- your partition number here
GPT ATTRIBUTES=0xC000000000000001
exit

0x0000000000000001 marks the partition as required.
0x8000000000000000 Prevents the partition from having a drive letter automatically assigned.
0x4000000000000000 Defines the partition's volume as hidden."