Restoring a disk drive from an image backup on an OS X system

I needed to restore an external USB-connected Toshiba disk drive from an image created with Disk Utility on a MacBook Pro running the OS X operating system. With the external disk drive attached, a diskutil command, diskutil list, showed the following:

$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            499.4 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *13.8 MB    disk2
   1:                  Apple_HFS C_PGP2FV_B_A0           13.8 MB    disk2s1
/dev/disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                  Apple_HFS TOSHIBA EXT             499.8 GB   disk3s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk3s3
$

Both the internal and external disk drives are 500 GB drives. I would expect the internal disk drive to be disk0 and the external one to have a higher disk number, e.g., disk3 in this case, and I can tell that is the case from "Apple_HFS TOSHIBA EXT" in the output. I can also confirm that with a diskutil info /dev/disk3 command, which shows that disk3 is, indeed, the Toshiba external USB drive.

$ diskutil info /dev/disk3
   Device Identifier:        disk3
   Device Node:              /dev/disk3
   Part of Whole:            disk3
   Device / Media Name:      TOSHIBA External USB 3.0 Media

   Volume Name:              Not applicable (no file system)

   Mounted:                  Not applicable (no file system)

   File System:              None

   Content (IOContent):      GUID_partition_scheme
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 USB
   SMART Status:             Not Supported

   Total Size:               500.1 GB (500107862016 Bytes) (exactly 976773168 512-Byte-Units)
   Volume Free Space:        Not applicable (no file system)
   Device Block Size:        512 Bytes

   Read-Only Media:          No
   Read-Only Volume:         Not applicable (no file system)
   Ejectable:                Yes

   Whole:                    Yes
   Internal:                 No
   OS 9 Drivers:             No
   Low Level Format:         Not supported

$

Following the instructions provided at Restore a full-disk .dmg file to a raw block device, I mounted the Apple Disk Image .dmg file as a block device with the following hdid command.

$ hdid -nomount "/Users/Shared/TOSHIBA EXT.dmg"
/dev/disk4

I could see from the output of the command that the TOSHIBA EXT.dmg file was designated as /dev/disk4 and I could also see it had that designation from a diskutil list command.

$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            499.4 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *13.8 MB    disk2
   1:                  Apple_HFS C_PGP2FV_B_A0           13.8 MB    disk2s1
/dev/disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                  Apple_HFS TOSHIBA EXT             499.8 GB   disk3s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk3s3
/dev/disk4
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            TOSHIBA EXT            *500.0 GB   disk4

I then tried restoring the disk drive's partitions and contents using the dd command dd if=/dev/disk4 of=/dev/disk3 bs=131072; the if parameter indicates the input device and the of parameter the output device. I set the block size to be 131072 as in the example. I received a "permission denied" message initially, which led me to realize that I needed to use the sudo command to run the command with elevated privileges. However, then I received a message indicating the account I was logged into wasn't in the sudoers file.

$ dd if=/dev/disk4 of=/dev/disk3 bs=131072
dd: /dev/disk3: Permission denied
$ sudo dd if=/dev/disk4 of=/dev/disk3 bs=131072
Password:
jasmith1 is not in the sudoers file.  This incident will be reported.

I dealt with that issue by clicking on Users & Groups under System Preferences, which is accessible by clicking on the Apple icon at the top left-hand corner of the screen, then selecting the account from the account list by clicking on it and then checking the box for "Allow user to administer the computer", which resulted in a window appearing stating "For this change to take effect, you must restart the computer." However, I was then able to run the dd command without rebooting the system, though when I next attempted to do so, I received a "Resource busy" message.

$ sudo dd if=/dev/disk4 of=/dev/disk3 bs=131072
Password:
dd: /dev/disk3: Resource busy

In the OS X Finder application, I clicked on the eject icon next to the drive under Devices to dismount the external USB drive. I was then able to successfully run the command and restore the drive from the disk image I had created previously.

$ sudo dd if=/dev/disk4 of=/dev/disk3 bs=131072
Password:
3814692+1 records in
3814692+1 records out
499999343104 bytes transferred in 19392.505352 secs (25783123 bytes/sec)
$

Restoring the data to the drive took over 5 1/2 hours. The transfer rate was about 197 Mbs (25783123 bytes/sec). At the conclusion of the restoration, I disconnected the USB cable from the drive to the laptop and then reconnected it. I was then able to see all of the original files on the system. And a diskutil info /dev/disk3 command showed the drive was now formatted with an NTFS partion as it had been when I purchased it rather than Apple's Hierachical File System (HFS) file system as it was prior to the start of the restore operation with dd.

$ diskutil info /dev/disk3
   Device Identifier:        disk3
   Device Node:              /dev/disk3
   Part of Whole:            disk3
   Device / Media Name:      TOSHIBA External USB 3.0 Media

   Volume Name:              TOSHIBA EXT

   Mounted:                  Yes
   Mount Point:              /Volumes/TOSHIBA EXT

   File System Personality:  NTFS
   Type (Bundle):            ntfs
   Name (User Visible):      Windows NT File System (NTFS)

   Content (IOContent):      None
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 USB
   SMART Status:             Not Supported

   Total Size:               500.1 GB (500107862016 Bytes) (exactly 976773168 512-Byte-Units)
   Volume Free Space:        499.7 GB (499712028672 Bytes) (exactly 976000056 512-Byte-Units)
   Device Block Size:        512 Bytes
   Allocation Block Size:    4096 Bytes

   Read-Only Media:          No
   Read-Only Volume:         Yes
   Ejectable:                Yes

   Whole:                    Yes
   Internal:                 No
   OS 9 Drivers:             No
   Low Level Format:         Not supported

$

References:

  1. Making an image of a disk drive using Disk Utility
    Created: Monday July 18, 2016
    Last modified: Monday July 18, 2016 9:14 PM
    MoonPoint Support
  2. Restore a full-disk .dmg file to a raw block device
    Date: April 14, 2009
    Mac OS X Hints

 

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