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This whole mess started with trying to encrypt Time Machine backups. I have a 4TB Lacie P9230 external drive which has been working for about a year just fine. The drive has been partitioned into two partitions, one for TM backups and other as archive and other stuff that isn't important or can be downloaded from the internet. When I tried to enable Time Machine encryption, the process failed and the backup partition disappeared. Disk Utility listed it as grey and couldn't mount it or something. Then I did the wisest thing and simply unplugged the drive's power cord and reconnected. Now it's in this weird state where the volume apparently doesn't have a file system nor does the backup partition. The archive partition has a file system (JHFS+) and it is visible in Finder, but all the folders are there but they empty even though Disk Utility shows the correct amount of data used. I did try reformatting the whole volume, copying /dev/zero but nothing worked.

diskutil list:

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS SSD                     250.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:                  Apple_HFS 1TB                     999.9 GB   disk1s2
/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk2
   1:                        EFI EFI                     1.1 GB     disk2s1
   2:          Apple_CoreStorage Backup                  1.5 TB     disk2s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk2s3
   4:                  Apple_HFS Data                    2.5 TB     disk2s4
/dev/disk3 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        +18.1 MB    disk3
   1:        Apple_partition_map                         32.3 KB    disk3s1
   2:                  Apple_HFS Flash Player            18.1 MB    disk3s2
/dev/disk4 (external, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS                        +1.5 TB     disk4
                             Logical Volume on disk2s2
                             97716389-E391-4260-BE72-82DBB2262907
                             Unlocked Encrypted

The drive in question is disk2. disk4 seems to be the logical CoreStorage volume for the backup partition.

diskutil info disk2:

 Device Identifier:        disk2
 Device Node:              /dev/disk2
 Whole:                    Yes
 Part of Whole:            disk2
 Device / Media Name:      P9230

 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:               4.0 TB (4000787030016 Bytes) (exactly 7814037168 512-Byte-Units)
 Volume Free Space:        Not applicable (no file system)
 Device Block Size:        4096 Bytes

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

 Device Location:          External
 Removable Media:          No

 Virtual:                  No
 OS 9 Drivers:             No
 Low Level Format:         Not supported

diskutil info disk2s2 (backup partition):

 Device Identifier:        disk2s2
 Device Node:              /dev/disk2s2
 Whole:                    No
 Part of Whole:            disk2
 Device / Media Name:      Backup

 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
 Media Type:               Generic
 Protocol:                 USB
 SMART Status:             Not Supported
 Disk / Partition UUID:    F212F25E-748A-4852-A09C-B05CAF59CC9A

 Total Size:               1.5 TB (1500000026624 Bytes) (exactly 2929687552 512-Byte-Units)
 Volume Free Space:        Not applicable (no file system)
 Device Block Size:        4096 Bytes

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

 Device Location:          External
 Removable Media:          No


 This disk is a Core Storage Physical Volume (PV).  Core Storage Information:
 PV UUID:                  DCC36047-2B99-4320-863A-B652DF658F87
 LVG UUID:                 99F7CF3E-95B4-4948-99CC-D7D48C3E2456

diskutil info disk2s4 (archive partition):

 Device Identifier:        disk2s4
 Device Node:              /dev/disk2s4
 Whole:                    No
 Part of Whole:            disk2
 Device / Media Name:      LaCie

 Volume Name:              Data

 Mounted:                  Yes
 Mount Point:              /Volumes/Data

 File System Personality:  Journaled HFS+
 Type (Bundle):            hfs
 Name (User Visible):      Mac OS Extended (Journaled)
 Journal:                  Journal size 196608 KB at offset 0x2464000
 Owners:                   Enabled

 Partition Type:           Apple_HFS
 OS Can Be Installed:      No
 Media Type:               Generic
 Protocol:                 USB
 SMART Status:             Not Supported
 Volume UUID:              025271FE-FB4B-3892-8D0D-5EC152813C38
 Disk / Partition UUID:    B1915DD8-4F93-49E7-9248-A6149F8C1989

 Total Size:               2.5 TB (2499444781056 Bytes) (exactly 4881728088 512-Byte-Units)
 Volume Free Space:        1.8 TB (1797338988544 Bytes) (exactly 3510427712 512-Byte-Units)
 Device Block Size:        4096 Bytes
 Allocation Block Size:    8192 Bytes

 Read-Only Media:          No
 Read-Only Volume:         No

 Device Location:          External
 Removable Media:          No

mdls on a folder in the somewhat working archive partition

kMDItemFSContentChangeDate = 2016-01-04 11:43:11 +0000
kMDItemFSCreationDate      = 2012-08-17 12:37:06 +0000
kMDItemFSCreatorCode       = ""
kMDItemFSFinderFlags       = 0
kMDItemFSHasCustomIcon     = 0
kMDItemFSInvisible         = 0
kMDItemFSIsExtensionHidden = 0
kMDItemFSIsStationery      = 0
kMDItemFSLabel             = 0
kMDItemFSName              = "folder name"
kMDItemFSNodeCount         = 10
kMDItemFSOwnerGroupID      = 99
kMDItemFSOwnerUserID       = 99
kMDItemFSSize              = 10
kMDItemFSTypeCode          = ""

At some point in time between my drive disconnect/reconnects, the mdls command returned 0 values for everything. Finder still doesn't show anything in the folder.

I have tried reformatting the volume in Disk Utility, but it either cannot unmount it or cannot write to the last block. I then tried running this sudo dd if=/dev/zero of=/dev/rdisk2 bs=64k which resulted in the following error:

dd: /dev/rdisk2: Input/output error
1+0 records in
0+0 records out
0 bytes transferred in 0.005369 secs (0 bytes/sec)

diskutil zeroDisk force /dev/disk2 didn't help either:

Started erase on disk2
Error: -69759: Securely erasing data to prevent recovery failed
Underlying error: 5: POSIX reports: Input/output error

I have ran out of things to try on this drive. I have started to wonder whether the drive itself is starting to fail, but it was working just fine before I started messing around with it. If anyone has a solution that could preserve the data that would be perfect, but I don't really expect that to be even possible. All the data is disposable so if I could just reformat it and get back to using it (unless it is failing).

E1: The archive partition has magically restored some of the data, meaning I can now access data in the drive that was previously missing. Some data is still missing and I don't have a spare drive with sufficient capacity where I could offload the data in case it is failing.

E2: The drive works perfectly when connected to another Mac. It shows that it is encrypting (0%), so I'll let it finish the encryption and reinstall OS X on my main machine so that once the drive is encrypted, I hope it will be detected normally.

  • Please add the output of sudo gpt -r show /dev/diskX after checking the disk identifier of the 4 TB disk with diskutil list. Replace diskX by the disk identifier found. – klanomath Mar 19 '16 at 17:08
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Apparently I was asking the wrong question. After attaching this "corrupted" drive to another Mac, it simply asked for the password and mounted the drives with all their data as normal. I let the other Mac finish the encryption process, reinstalled OS X on my main machine and reconnected the drive and it now works perfectly.

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