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?
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