Столкнулся впервые с таким интересным кейсом.

Подключил внешний HDD с необходимыми бекапами, который имеет вроде как ext4 и важные данные. При попытке маунта — ругнулся на неизвестную ФС.

Ну все, подумал я, вот и конец бекапам.

Начал смотреть, разбираться с партициями и что там внутри, с удивлением обнаружил некий раздел, распознающийся fdisk-ом как Microsoft Basic Data.

После недолгого гуглинга наткнулся на эту статью — http://www.rodsbooks.com/linux-fs-code/

Вкратце — на gpt-дисках, кодовое обозначение для ФС пересекается с Microsoft ФС, что и приводит в итоге к неправильному опознанию раздела в Linux и его утилитами.

Выход есть, отмечу здесь на случай смерти линки.

If you have an existing dual-boot installation and you want the Linux partitions to disappear from the Windows file browser, the easiest way to accomplish this goal is to use GPT fdisk, version 0.7.2 or later. You can use the t command in the gdisk utility to do the job. Change the type code from 0x0700 to 0x8300:

# gdisk /dev/sdb
GPT fdisk (gdisk) version 0.8.2

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): p
Disk /dev/sdb: 625142448 sectors, 298.1 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): B58D5E92-7BFB-4488-94B9-2F1BCFDD86DB
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 625142414
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048          514047   250.0 MiB   EF00  EFI System
   2          514048          923647   200.0 MiB   0700  Spare /boot
   3          923648       625142414   297.7 GiB   8E00  Linux LVM

This example shows a GPT disk (as evidenced by the GPT: present line) with a Linux filesystem (Spare /boot) that has a 0x0700 type code—GPT fdisk’s way of identifying a Microsoft Basic Data partition. (Since GPT fdisk doesn’t scan partitions’ contents to identify the filesystem, you’ll have to know enough about your disk to know which partitions are actually Linux filesystem partitions.) This disk also has an EFI System Partition (ESP) and a Linux LVM partition. To change the type code of the Linux partition, use the t command to set a code of 0x8300 (GPT fdisk’s internal code for the Linux Filesystem Data type):

Command (? for help): t
Partition number (1-3): 2
Current type is 'Microsoft basic data'
Hex code or GUID (L to show codes, Enter = 8300): 8300
Changed type of partition to 'Linux filesystem'

To be sure everything is OK, you can view the partition table again, and then save your changes:

Command (? for help): p
Disk /dev/sdb: 625142448 sectors, 298.1 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): B58D5E92-7BFB-4488-94B9-2F1BCFDD86DB
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 625142414
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048          514047   250.0 MiB   EF00  EFI System
   2          514048          923647   200.0 MiB   8300  Spare /boot
   3          923648       625142414   297.7 GiB   8E00  Linux LVM

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT).
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot.
The operation has completed successfully.