Convert filesystem NTFS -> EXT4?
Just for the record, there is a software (actually, a mini-distro) that does exactly the procedure arrange said in enzotib's answer:
Parted Magic
It looks like a direct conversion from NTFS to ext4, but internally the procedures are:
- Shrink the NTFS partition
- Create an ext4 partition in the empty space
- Move data from NTFS to ext4 until ext4 is full
- If NTFS is empty (all data was moved), go to step 8
- Shrink NTFS
- Enlarge ext4
- Repeat steps 3 to 6 until done
- Delete NTFS partition
- Move ext4 partition to NTFS' orignal place
- Trim ext4 partition to NTFS' original size
So the more occupied your NTFS partition is, the longer it will take. If it is less than 50%, it will convert in one pass, in a single shrink-copy-enlarge iteration.
Although Parted Magic conveniently automates all of this, it is still essentially the same procedures described by arrange, so it is very risky and very time consuming. Backup-format-restore is much safer and much faster.
No, there is no way that I am aware of.
The only way, as you said, is to backup->format->restore.
Actually there IS a way to do this almost directly.
You could easily convert NTFS to ext2 / ext3 with anyconvertfs from anyfs-tools
Then you could convert it to ext4 using tune2fs.