Format a USB flash drive using gpart

[Thomas Mueller]

On Sat, 07 Jul 2012 17:45:17 -0400, Thomas Mueller wrote:
> Does a USB flash drive also work as a giant floppy, no partitions?
> Can you make a flash drive bootable when nonpartitioned and
> formatted that way?

Polytropon responded:

> Yes, that's exactly what my advice was aiming to, but let's
> try to keep the terminology clean: You cannot do without
> partitions. A partition carries a file system.

> You _can_ do without slices. A slice holds one or more partitions.
> A slice is a "DOS primary partition". Omitting it is called
> "dedicated mode". There may be some circumstances where a
> dedicated disk doesn't boot. Personally I haven't met one,
> but it's still possible due to BIOSes expecting MS-DOS-alike
> structures.

> For the file system side, it's just a matter of having
> created one partition covering the whole disk, newfs and
> tunefs it, and install the boot code. Wojciech Puchar did
> already explain how this works and which tools are involved.

> However, there _is_ a way to make a "giant floppy without a
> file system" (as you said without partitions, and I'll take
> that literally): You can use tar, "the universal file system
> that isn't a file system" to write data to the USB stick.

> Writing stuff:

>         # tar cf /dev/da0 /my/files

> Reading stuff:

>         # tar xf /dev/da0

> This works, but it may appear that no other system can read it.
> If you consider using it for FreeBSD only, no problem. The big
> advantage: You don't need to mount and umount the stick.

> I'm assume _that_ construct cannot be booted.

You mean the non-subdivided 1.44 MB or other capacity of a floppy is called a partition?

Same question for CDs?

One does not usually think of something that can't be created by subdividing as a partition.

Also, a file system can be contained in an image file.  Or is this a virtual partition?

Might 
 # tar xf /dev/da0
work in other BSDs or even other (quasi-)Unixes including Linux, using the appropriate device name where applicable in place of da0?

While that particular construst could probably not be booted, it is possible to boot from a floppy or image file that does not contain a file system.

Some of the disk images on the System Rescue CD (sysresccd.org) are not viewable/mountable as file systems.

Tom