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My FV-encrypted external drive was working fine, and now it's not.

In Disk Utility (GUI), it shows as "Unformatted".

diskutil list:

    /dev/disk2 (external, physical):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *2.0 TB     disk2
       1:                        EFI EFI                     209.7 MB   disk2s1
       2:          Apple_CoreStorage iMax Backup 2018-12-22  2.0 TB     disk2s2
       3:                 Apple_Boot Recovery HD             650.0 MB   disk2s3

Obviously it’s “iMax Backup 2018-12-22” I want back.

sudo gpt -r show /dev/disk2:

       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6         
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640  3905087808      2  GPT part - 53746F72-6167-11AA-AA11-00306543ECAC
  3905497448     1269536      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  3906766984      262150         
  3907029134          32         Sec GPT table
  3907029166           1         Sec GPT header

First Aid in Disk Utility:

Running First Aid on “Seagate BUP Slim RD Media” (disk2)

Checking prerequisites
Checking the partition list
Checking the partition map size
Checking for an EFI system partition
Checking the EFI system partition’s size
Checking the EFI system partition’s file system
Checking the EFI system partition’s folder content
Checking all HFS data partition loader spaces
Checking booter partitions
Checking booter partition disk2s3
Verifying file system.
Volume is already unmounted.
Performing fsck_hfs -fn -x /dev/rdisk2s3
Checking Journaled HFS Plus volume.
Checking extents overflow file.
Checking catalog file.
Checking multi-linked files.
Checking catalog hierarchy.
Checking extended attributes file.
Checking volume bitmap.
Checking volume information.
The volume Recovery HD appears to be OK.
File system check exit code is 0.
Restoring the original state found as unmounted.
Checking Core Storage Physical Volume partitions
Verifying storage system
Performing fsck_cs -n -x --lv --uuid E994BCCD-8FF0-44D2-AE64-8D3CA172EAA5
Checking volume
disk2s2: Scan for Volume Headers
disk2s2: Scan for Disk Labels
Logical Volume Group E994BCCD-8FF0-44D2-AE64-8D3CA172EAA5 on 1 device
disk2s2: Scan for Metadata Volume
Logical Volume Group has a 24 MB Metadata Volume with double redundancy
Start scanning metadata for a valid checkpoint
Load and verify Segment Headers
Load and verify Checkpoint Payload
Load and verify Transaction Segment
Incorporate 0 newer non-checkpoint transactions
Load and verify Virtual Address Table
Load and verify Segment Usage Table
Load and verify Metadata Superblock
Load and verify Logical Volumes B-Trees
Unable to bootstrap transaction group 236233: cksum mismatch
Continue scanning metadata for an older checkpoint
Load and verify Segment Headers
Load and verify Checkpoint Payload
Load and verify Transaction Segment
Incorporate 0 newer non-checkpoint transactions
Load and verify Virtual Address Table
Load and verify Segment Usage Table
Load and verify Metadata Superblock
Load and verify Logical Volumes B-Trees
Unable to bootstrap transaction group 236232: cksum mismatch
Continue scanning metadata for an older checkpoint
Load and verify Segment Headers
Load and verify Checkpoint Payload
Load and verify Transaction Segment
Incorporate 0 newer non-checkpoint transactions
Load and verify Virtual Address Table
Load and verify Segment Usage Table
Load and verify Metadata Superblock
Load and verify Logical Volumes B-Trees
Unable to bootstrap transaction group 236231: cksum mismatch
Continue scanning metadata for an older checkpoint
Load and verify Segment Headers
Load and verify Checkpoint Payload
Load and verify Transaction Segment
Load and verify Transaction Segment
Load and verify Transaction Segment
Incorporate 2 newer non-checkpoint transactions
Load and verify Virtual Address Table
Load and verify Segment Usage Table
Load and verify Metadata Superblock
Load and verify Logical Volumes B-Trees
Unable to bootstrap transaction group 236228: cksum mismatch
No valid commit checkpoint found
The volume E994BCCD-8FF0-44D2-AE64-8D3CA172EAA5 was found corrupt and needs to be repaired
Storage system check exit code is 1.
Problems were found with the partition map which might prevent booting

Operation successful.

which reports:

First Aid found corruption that needs to be repaired. To repair the
startup volume, run First Aid from Recovery. Click Done to continue.

(I tried it in Recovery mode. It said the same thing.)

TechTool Pro said it might have to reformat the disk to fix the partition map. DiskWarrior will only upgrade my ancient version by snail mail.

Unfortunately I have no idea what the GPT or First Aid stuff means. Can anybody who does tell me if there any hope of getting back my FV volume, and if so, how? (I don't have the original. Today was the day I was going to restore files from the backup.)

Thank you.

2019 iMac, Mojave 10.14.5.

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