I'm trying to do a complete backup of my wife's MB from my MBP. I booted the MB into Firewire Target Disk Mode, then used Disk Utility on my MBP to make a DMG of it onto another external FW drive. Here's the log from Disk Util:

Notarize a dmg 'no mountable file systems' Suddenly the notarization service failed with message: 'b'hdiutil: attach failed - no mountable file systems ', but I can mount the dmg in my mac. Until few days ago, notarization by same build process on CI works as expected. A small but noticeable number of Mac users are unable to open our DMG installer for Mac. The Mac presents a 'no mountable file system' error when the user attempts to open the DMG for installation. Each time we try to follow up (these reports come via e-mail), we don't hear back but would like to get to the bottom of this.

Dmg No Mountable File Systems Catalina

2008-03-22 15:07:40 -0700: Disk Utility started.
2008-03-22 15:08:32 -0700: Creating Image “TiffanyBook032208.dmgÂ”
2008-03-22 15:08:40 -0700: Preparing imaging engineÂ…
2008-03-22 15:08:44 -0700: Reading Driver Descriptor Map (DDM : 0)Â…
2008-03-22 15:08:44 -0700: (CRC32 $51B6B901: Driver Descriptor Map (DDM : 0))
2008-03-22 15:08:44 -0700: Reading Apple (Apple_partition_map : 1)Â…
2008-03-22 15:08:44 -0700: (CRC32 $A3D7DA6A: Apple (Apple_partition_map : 1))
2008-03-22 15:08:44 -0700: Reading (Apple_Free : 2)Â…
2008-03-22 15:08:45 -0700: (CRC32 $00000000: (Apple_Free : 2))
2008-03-22 15:08:45 -0700: Reading Apple_HFS_Untitled_1 (Apple_HFS : 3)Â…
2008-03-22 15:57:57 -0700: (CRC32 $CE3D7CF0: Apple_HFS_Untitled_1 (Apple_HFS : 3))
2008-03-22 15:57:57 -0700: Reading (Apple_Free : 4)Â…
2008-03-22 15:57:58 -0700: (CRC32 $00000000: (Apple_Free : 4))
2008-03-22 15:57:58 -0700: Adding resourcesÂ…
2008-03-22 15:57:59 -0700: Elapsed Time: 49m 13.314s
2008-03-22 15:57:59 -0700: File size: 28521921586 bytes, Checksum: CRC32 $C61693A6
2008-03-22 15:57:59 -0700: Sectors processed: 312581808, 79974513 compressed
2008-03-22 15:57:59 -0700: Speed: 13.2Mbytes/sec
2008-03-22 15:57:59 -0700: Savings: 82.2%
2008-03-22 15:58:01 -0700: Image Â“TiffanyBook032208.dmgÂ” created successfully.
2008-03-22 16:08:24 -0700: Name : TiffanyBook032208.dmg
Type : Unattached Disk Image
Disk Name : /Cow-e-fornia/Backup/TiffanyBook032208.dmg
Disk Image Path : /Volumes/Cow-e-fornia/Backup/TiffanyBook032208.dmg
Disk Image Size : 26.6 GB (28,521,921,586 Bytes)
Location : External
2008-03-22 16:08:24 -0700:
2008-03-22 16:10:51 -0700: Attach Image Â“TiffanyBook032208.dmgÂ”
2008-03-22 16:10:51 -0700: InitializingÂ…
2008-03-22 16:10:57 -0700: VerifyingÂ…
2008-03-22 16:10:58 -0700: Driver Descriptor Map (DDM : 0): verified CRC32 $51B6B901
2008-03-22 16:10:59 -0700: Apple (Apple_partition_map : 1): verified CRC32 $A3D7DA6A
2008-03-22 16:11:00 -0700: (Apple_Free : 2): verified CRC32 $00000000
2008-03-22 16:32:14 -0700: Apple_HFS_Untitled_1 (Apple_HFS : 3): verified CRC32 $CE3D7CF0
2008-03-22 16:32:15 -0700: (Apple_Free : 4): verified CRC32 $00000000
2008-03-22 16:32:15 -0700: Verification completedÂ…
2008-03-22 16:32:15 -0700: verified CRC32 $C61693A6
2008-03-22 16:32:15 -0700: AttachingÂ…
2008-03-22 16:32:16 -0700: Checking volumesÂ…
2008-03-22 16:33:14 -0700: Volume check completedÂ…
2008-03-22 16:33:14 -0700: AttachingÂ…
2008-03-22 16:33:14 -0700: FinishingÂ…
2008-03-22 16:34:06 -0700: Unable to attach Â“TiffanyBook032208.dmgÂ”. (no mountable file systems)

When I tried to mount the image, it went through a 20 minute verification procedure, then failed with the 'no mountable file systems' error.
I tried mounting it from Finder by double-clicking the DMG and got the same error. So I deleted the DMG and re-created it from scratch (including rebooting the MB into TDM):

Mac No Mountable File System

2008-03-22 16:37:22 -0700: Disk Utility started.
2008-03-22 16:37:54 -0700: Creating Image Â“TiffanyBook032208.dmgÂ”
2008-03-22 16:37:58 -0700: Preparing imaging engineÂ…
2008-03-22 16:38:02 -0700: Reading whole disk (Apple_HFS : 0)Â…
2008-03-22 17:29:22 -0700: (CRC32 $DB22F44F: whole disk (Apple_HFS : 0))
2008-03-22 17:29:23 -0700: Adding resourcesÂ…
2008-03-22 17:29:25 -0700: Elapsed Time: 51m 20.825s
2008-03-22 17:29:25 -0700: File size: 28525037851 bytes, Checksum: CRC32 $7D6B0BB2
2008-03-22 17:29:25 -0700: Sectors processed: 312319584, 79999257 compressed
2008-03-22 17:29:25 -0700: Speed: 12.7Mbytes/sec
2008-03-22 17:29:25 -0700: Savings: 82.2%
2008-03-22 17:29:27 -0700: Image Â“TiffanyBook032208.dmgÂ” created successfully.

I get the same failure, whether mounting from Finder or from Disk Utility.

Sparsebundle No Mountable File Systems

WTF? Does anyone know what might be going on? I came > < this close to repartitioning her HDD, then I got the willies and decided to verify the image first. Good thing I'm paranoid, otherwise my wife would have had a factory-fresh MB right about now. -- View image here: https://cdn.arstechnica.net/forum/smilies/scared_classic.gif --

Dmg Not Mountable File System