This morning, my iMac show me the prohibit sign. After hours of struggling, I'm facing this: the Mac does not want to boot up. I have a lot of recent files to recover, but have this issue:

root# diskutil info disk0s2
Device Identifier:        disk0s2
Device Node:              /dev/disk0s2
Part of Whole:            disk0
Device / Media Name:      iMac HDD
Volume Name:              Not applicable (no file system)
Mounted:                  Not applicable (no file system)
File System:              None
Partition Type:           Apple_CoreStorage
OS Can Be Installed:      No
Recovery Disk:            disk0s3
Media Type:               Generic
Protocol:                 SATA
SMART Status:             Verified
Disk / Partition UUID:    0F0B3B70-6807-47A4-BED7-0BD2B77E4F51
Total Size:               998.7 GB (998695010304 Bytes) (exactly 1950576192 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:                No
Whole:                    No
Internal:                 Yes
Solid State:              No

This disk is a Core Storage Physical Volume (PV).  Core Storage Information:
PV UUID:                  4EBFF6EA-D253-4575-99C3-93FFD136543F
LVG UUID:                 F98A23E2-C1B9-499E-BC45-B971D2AE251F

then, the core storage info :

root# diskutil cs info disk0s2
Core Storage Properties:
Role:                       Physical Volume (PV)
UUID:                       4EBFF6EA-D253-4575-99C3-93FFD136543F
Parent LVG UUID:            F98A23E2-C1B9-499E-BC45-B971D2AE251F
Device Identifier:          disk0s2
PV Size:                    998695010304 B
PV Status:                  Checking

the list of dev for core storage :

root# diskutil cs list
CoreStorage logical volume groups (1 found)
+-- Logical Volume Group F98A23E2-C1B9-499E-BC45-B971D2AE251F
    Name:         Macintosh HD
    Status:       Offline
    Size:         998695010304 B (998.7 GB)
    Free Space:   -none-
    +-< Physical Volume DDD40234-2DC7-44B2-BE95-D9C0FA46F96A
    |   ----------------------------------------------------
    |   (No properties)
    +-< Physical Volume 4EBFF6EA-D253-4575-99C3-93FFD136543F
        Index:    1
        Disk:     disk0s2
        Status:   Checking
        Size:     998695010304 B (998.7 GB)

and finaly, an attempt to check the partition :

root# fsck_cs /dev/disk0s2
   Executing fsck_cs (version 471.30.1)
** Checking volume
** disk0s2: Scan for Volume Headers
** disk0s2: Scan for Disk Labels
** Logical Volume Group F98A23E2-C1B9-499E-BC45-B971D2AE251F spans 2 devices
** Incomplete or inconsistent CoreStorage Physical Volume set

And I cannot remount the disk.

I've read some things about rewriting the MBR and/or GPT. Is this the way to recover my datas?

If I do a disk dump (dd) of this disk, then perform a fresh re-install, is there any change I'll can open the disk dump afterward? I've seen things using Apple "ars" tool, but, I'm not sure it'll help.

Any ideas?

Note: from a hardware point of view, the disk is ok, I can do a dd if=/dev/disk0 of=/dev/null without any errors.

  • Try a dd, work on the copy, and simply remove the missing PV entry. – John Keates Apr 14 '16 at 15:08

Your CoreStorage Logical Volume Group is missing a Physical Volume with the UUID DDD40234-2DC7-44B2-BE95-D9C0FA46F96A.

Your internal drive probably is (or worse: was) a Fusion Drive and the SSD part is missing. The SSD is either damaged or has to be reseated, if it doesn't show up entering diskutil list or if it shows up: the internal structure of the LVG got corrupted.

A Fusion Drive works similar as a RAID0: 2 (or more) disks occur as one: The whole file system spans over two or more disks. One big difference of a Fusion Drive is that files often aren't sliced and therefore either reside on the SSD or the HDD. Depending on the file type and the access frequency or last access time the "less important" files are relocated to the HDD part. The file system files (e.g. catalog file) and most system files usually reside on the SSD part.

You may try to dd disk0s2 to an external drive (either as partition or as raw file to an existing volume) and inspect it with a decent file recovery tool. If you enabled FileVault previously the data can't be recovered.

Rewriting the GPT (or MBR) doesn't help at all or on the contrary: it makes things worse.

If you have further questions leave a comment.

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