What is the proper way to use dd
(or anything else – asr
?) to create an image of a corrupted yet readable Windows disk?
If what I am using (see below) is correct, then is it possible that an image of a disk would not be mountable when the original disk is?
Background info:
The disk's file system is not readable on a Windows system: the disk shows up as "raw" in disk management. It is however readable in macOS (10.14) and I am able to copy individual files from it.
The goal however is to copy the entire disk if possible to a readable image and then work with that image (repair partition table, recover remaining files) rather than with the failing disk that I am afraid can quit at any moment.
Here is the command I've been using to image a 500GB Windows disk that came from a Dell computer and that has a number of bad blocks and apparently a corrupted partition table:
sudo dd if=/dev/rdisk3 of=/Volumes/exFAT_Vol/rdiskX.dmg bs=4M conv=noerror,sync
Copies fast (40MB/s via USB 2.0) but doesn't seem to create a correct (mountable) image: "no mountable file systems" when trying to mount it in Finder.
Some sources (e.g. Recover a dead hard drive using dd from 2005) suggest using bs=512
and it's in progress now – yet copies at around 4MB/s which will take more than a day to complete – and I am not even sure it'll work.
Some of the relevant info on the disk and its partitions:
Volume type : Physical Device
BSD device node : disk3
Connection : USB
Device tree path : IODeviceTree:/PCI0@0/XHC1@14
Writable : No
Is case-sensitive : No
Volume capacity : 500,107,862,016
Available space (Purgeable + Free) : 0
Purgeable space : 0
Free space : 0
Used space : 500,107,862,016
Owners enabled : No
Is encrypted : No
Can be verified : No
Can be repaired : No
Bootable : No
Journaled : No
Disk number : 3
Media name : Generic External Media
Media type : Generic
Ejectable : Yes
Solid state : No
S.M.A.R.T. status : Not Supported
Volume type : Physical Volume
BSD device node : disk3s2
Mount point : /Volumes/Untitled
File system : Windows NT File System (NTFS)
Connection : USB
Device tree path : IODeviceTree:/PCI0@0/XHC1@14
Writable : No
Is case-sensitive : No
File system UUID : AC8CB496-EAD2-47A2-BB36-2A981976BC2B
Volume capacity : 500,064,122,880
Available space (Purgeable + Free) : 373,903,597,568
Purgeable space : 0
Free space : 373,903,597,568
Used space : 126,160,525,312
File count : 176,730
Owners enabled : No
Is encrypted : No
System Integrity Protection supported : No
Can be verified : No
Can be repaired : No
Bootable : No
Journaled : No
Disk number : 3
Partition number : 2
Media name :
Media type : Generic
Ejectable : Yes
Solid state : No
S.M.A.R.T. status : Not Supported
Parent disks : disk3
Best Answer
Based on what I've done so far and the comments I've read on "Recover a dead hard drive using dd":
dd
fails to image or clone damaged media to make the result equally mountable or readable, in multiple instances including mine;In more detail:
ASR
) that can clone or image damaged yet readable media.ASR
(or its GUI sibling, Disk Utility) will bail out once there is an I/O error such as bad blocks on the media.ddrescue
ordd_rescue
mentioned in the linked article) - my answer is only about tools that are part of stock macOS.The answer is based on multiple comments in "Recover a dead hard drive using dd" that mirror my experience:
dd
completes yet the image can't be mounted. I.e.dd
does not appear to have created a close enough image of the media.Here is what I have tried:
sudo dd if=/dev/rdiskX of=/Volumes/exFAT_Vol/image.dmg bs=4M conv=noerror,sync
andsudo dd if=/dev/rdiskXsY of=/Volumes/exFAT_Vol/image.dmg bs=4M conv=noerror,sync
to image the media. Neither image can be mounted, with errors such as "the following disks couldn't be opened: no mountable file systems".sudo dd if=/Volumes/exFAT_Vol/image.dmg of=/dev/rdiskZ bs=4M conv=noerror,sync
- with a similar result: the physical media can't be mounted, and unlike the original damaged one, doesn't display the partition information such as "File system : Windows NT File System (NTFS)
".Fixing damaged partition map. The operation couldn’t be completed. (com.apple.DiskManagement error -69874.) Operation failed…
.What I haven't yet tried:
dd
with a differentbs=
value such as512
, instead of4m
. Takes too long.dd
without theconv=sync
option, i.e. just useconv=noerror
one. (Just didn't have a chance to try it yet - each attempt takes 4-5 hours.)dd
with conventional rather than raw devices - e.g./dev/disk4
rather than/dev/rdisk4
.dd
, Disk Utility,asr
.Hope this helps someone else in the same situation and really hope my answer is wrong: i.e. hope that there is a way to make
dd
work in this situation, to make mountable images off damaged yet readable / mountable media.