I'm using a 160GB Hitachi External HDD. When I was creating partitions, I accidentally formatted it from NTFS to RAW.
I tried to format it back to NTFS, but I got an error ("could not format").
I then tried to run chkdsk on it, but chkdsk doesn't work with RAW.
So then I tried with DiskPart, but the same formatting error occurred ("the request could not be performed because of an i/o device error").
I don't care if I lose any data, I just want to get my disk back in a usable state.
Boot from a Linux LiveCD/USB and try GParted (or perhaps from GParted's own Debian-based LiveCD/USB).
If that doesn't work, see if you can take the drive out of the case (obviously don't do it if it'll void the warranty) and directly attach it to a desktop so you can run GParted on it.
On Gparted you'll have to "Create a new Partition Table" and then create any partition you'd like because it's going to format for it.
If you still get I/O errors or GParted fails, use WinDFT and run an Extended/Thorough Test on the drive. If that passes, Erase the Disk and attempt to repartition:
If Windows reports a partition as RAW, it means it couldn't identify any file system on the partition that it understands. So if you were using Windows to partition the disk (sounds like it) and reformatted the partition(s), and they ended up as RAW, that means the format operation failed in a rather catastrophic fashion, possibly due to the I/O errors you mention.
I/O errors means the disk is having trouble reading or writing, either a certain area or generally. (I/O is short for input/output.)
Since you don't care about the data, my advice would be to hand in the disk for electronics recycling, and get a new one. The cost of an external disk of that size is relatively trivial these days, and even if you can get it working again perhaps by fiddling with partition starts etc., you will never be able to trust it to retain data in a readable manner.
Hard disks these days have extensive error-correcting capabilities; when you start seeing I/O errors, that means that the built-in error correction is no longer able to correct for the errors. That normally means the disk is very close to outright failing, if it hasn't already failed.
Try my way: Right click “My Computer” and select “Manage” => Open “Device Manager” and find your drive under the Disk Drives heading => Right click drive and select “Properties” => Choose “Policies” tab and select the "Optimize for performance" option => Click OK => Open "My Computer"=> Select "Format" on the flash drive
Next time, if this happens... and if you dont care about your data, just use a DBAN LiveCD to blank the HDD, and create new partitions with GParted.
