Ubuntu – Capacity of pen drive shown is less than the actual

14.04gnome-disk-utilitygpartedpartitioningusb-drive

I have a 8 GB pendrive. I used to write raw data into the pendrive (without creating filesystem) using the dd command.

Today, when I inserted the pen drive, the I am unable to write anything on to it. When I open gparted it is showing the total space on the pen drive as 500 MB. I am unable to create a new partition table or a partition on the pen drive now.

Here is the fdisk -l output.

Disk /dev/sdb: 0 MB, 512000 bytes
255 heads, 63 sectors/track, 0 cylinders, total 1000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00095df6

What's wrong with the pen drive? How can I recover the lost space?

Device Boot      Start         End      Blocks   Id  System

When I open gnome-disks, it shows the total space as 8 GB but when I try to create a new partition using it, it shows the following error:

Error creating partition on /dev/sdb: Command-line parted --align optimal --script "/dev/sdb" "mkpart primary ext2 1MiB 7969177599b"' exited with non-zero exit status 1: Error: The location 7969177599b is outside of the device /dev/sdb.
 (udisks-error-quark, 0)

Best Answer

These instructions worked for me to reformat an 8GB USB flash drive that was made useless after I used dd to write a bootable iso file to the flash drive. I reformatted the flash drive to its original FAT32 format as follows:

  1. Remove all of your USB devices except for the 8GB USB flash drive that you want to reformat, so you won't get confused about the device name of the USB flash drive later on.

  2. List all the partitions.

     sudo fdisk -l
    

    Search the results of the command for output that looks like this:

     Disk /dev/sdc: 7864 MB, 7864320000 bytes
     30 heads, 33 sectors/track, 15515 cylinders, total 15360000 sectors
     Units = sectors of 1 * 512 = 512 bytes
     Sector size (logical/physical): 512 bytes / 512 bytes
     I/O size (minimum/optimal): 512 bytes / 512 bytes
     Disk identifier: 0x00016288
    
        Device Boot      Start         End      Blocks   Id  System
     /dev/sdc1   *        2048    15359999     7678976    b  W95 FAT32
    

    If you see something like 7864 MB (8GB) in the output (see the example output above), then that is your 8GB USB flash drive. In this example it is called /dev/sdc. Now open the Disks application from the Dash and check again to make sure that the device name of your 8GB flash drive is the same as what you got from running the command: sudo fdisk -l.

  3. Create a partition table on the disk of type msdos, sometimes known as Master Boot Record (MBR).

     sudo parted /dev/sdc mklabel msdos
    

    In this example I used /dev/sdc for the name of the device which is what was found in the results of step 2. I can't stress strongly enough how important it is to verify the device name before running this step!

    Warning: If you type the wrong device name you may overwrite your operating system or another one of your partitions containing important personal files!!! So be careful and check the device name a second time. Open the Disks application and check the device name of your 8GB USB flash drive in Disks. It should be the same device name!!! Now check again! You don't want to accidentally type the wrong device name!

  4. Add an empty "primary" partition, which will hold a FAT filesystem later.

     sudo parted -a none /dev/sdc mkpart primary fat32 0 8192 
    

    Once again in this example I used /dev/sdc for the name of the device which is what was found in the results of step 2. The command specifies the start point (from 0 MB) to the end point (8192 MB). If the 8GB USB flash drive does not have the full 8192 MB space, parted will adjust it automatically. If the terminal returns a message that the start point can't start at 0 MB and you have to use some other small number close to 0 MB, type Y to accept this. Note the command is creating a single, primary partition on the whole disk.

    This newly created partition will have the ID /dev/sdc1. That is because the device name in this example is /dev/sdc and the 1 at the end is because it is the first partition on that device.

  5. Create a FAT filesystem on the /dev/sdc1 partition by formatting the partition.

     mkfs.vfat -n "8GB-USB" /dev/sdc1
    

    /dev/sdc1 is the partition ID from step 4. "8GB-USB" is the partition label, which can be your own choice of label, just enclose the label inside two double quote characters.

You now have a ready-to-use reformatted USB flash drive with an 8GB FAT partition.