I'm trying to make a 40GB ext3 local loopback file system. This loopback filesystem is stored on my NAS which is mounted on a Ubuntu Precise 12.04 x64 machine using NFS. The machine has both read and write permissions on the NAS. 

I've created a 40GB file for use by running `dd if=/dev/zero of=/media/vps/Ironman.ext3 bs=1024 count=40000000`. The file was successfully created, so I mounted is as a loopback system in `/dev/loop0` by running `sudo losetup /dev/loop0 /media/vps/Ironman.ext3`. 

I'm now trying to format this as a ext3 file system by running `sudo mkfs -t ext3 -q /media/vps/Ironman.ext3`. However, whenever I run this command I get the following output:

```
mke2fs 1.42 (29-Nov-2011)
/media/vps/Ironman.ext3 is not a block special device.
Proceed anyway? (y,n) y
/media/vps/Ironman.ext3: Permission denied while setting up superblock

```

How can I get around this, and format the loopback device as ext3?

**Update 1**

I've just tried to format it using the loopback device, as seen below. I am still, however, getting permission denied. You can see in the first set the file was already mounted. 

```
danielsgroves@precise64:/dev$ sudo losetup /dev/loop0
/dev/loop0: [0015]:26378243 (/media/vps/Ironman.ext3)
danielsgroves@precise64:/dev$ sudo mkfs -t ext3 -q /dev/loop0
/dev/loop0: Operation not permitted while setting up superblock

```

**Update 2**

With verbose output

```
danielsgroves@precise64:/dev$ sudo mkfs -t ext3 -v /dev/loop0
mke2fs 1.42 (29-Nov-2011)
fs_types for mke2fs.conf resolution: 'ext3'
/dev/loop0: Operation not permitted while setting up superblock

```