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Conclusion

I am disturbed and surprised at the same time, that the OP has hidden the important fact, that it is an iPod, or some other Apple product, and not an ordinary USB DISK, from us. But anyway, posting this for reference, and for future readers.

_{This serves as an addition to the accepted answer and also as a potential source of possibly important facts, which were untold by the OP. This should normally not happen and you shall not intentionally redact / hide / manually edit any command outputs like your fdisk.}

Today I needed to restore some of my oldest audio collection, no I did not backup my MP3s. So, I remembered I had some old iPod (4GB), I plugged it into the USB, and voila, I see some very similar and strange partitioning like the OP posted:

# fdisk -l /dev/sdb Disk /dev/sdb: 3,78 GiB, 4055885824 bytes, 1980413 sectors Disk model: iPod  Units: sectors of 1 * 2048 = 2048 bytes Sector size (logical/physical): 2048 bytes / 2048 bytes I/O size (minimum/optimal): 2048 bytes / 2048 bytes Disklabel type: dos Disk identifier: 0x6f20736b Device Boot Start End Sectors Size Id Type /dev/sdb1 778135908 1919645538 1141509631 2,1T 72 unknown /dev/sdb2 168689522 2104717761 1936028240 3,6T 65 Novell Netware 386 /dev/sdb3 1869881465 3805909656 1936028192 3,6T 79 unknown /dev/sdb4 2885681152 2885736650 55499 108,4M d unknown Partition table entries are not in disk order. 

You see the resemblance?!

I went on checking the system log, attaching for completeness:

My iPod supports only FAT32 as per this excerpt from the following file:

=

Conclusion

_{This serves as an addition to the accepted answer and also as a potential source of possibly important facts, which were untold by the OP. This should normally not happen. You shall not intentionally redact / hide / manually edit any command outputs like your fdisk, for any reasons other than hiding some sensitive information like serial numbers, for example.}

Today, I needed to restore some of my oldest audio collection,.. no, I did not backup my MP3s. So, I remembered I had some old Apple iPod (4GB). I plugged it into the USB, and voila, I see some very similar, and particularly strange, partitioning like the OP posted:

# fdisk -l /dev/sdb   Disk /dev/sdb: 3,78 GiB, 4055885824 bytes, 1980413 sectors Disk model: iPod Units: sectors of 1 * 2048 = 2048 bytes Sector size (logical/physical): 2048 bytes / 2048 bytes I/O size (minimum/optimal): 2048 bytes / 2048 bytes Disklabel type: dos Disk identifier: 0x6f20736b Device Boot Start End Sectors Size Id Type /dev/sdb1 778135908 1919645538 1141509631 2,1T 72 unknown /dev/sdb2 168689522 2104717761 1936028240 3,6T 65 Novell Netware 386 /dev/sdb3 1869881465 3805909656 1936028192 3,6T 79 unknown /dev/sdb4 2885681152 2885736650 55499 108,4M d unknown Partition table entries are not in disk order. 

You see the resemblance?!

Intereestingly, as you can see, the primary file system resides on the device itself and not in those partitions we can see with fdisk. We could argue, that such an engineering is wrong, but Apple won't change, I suppose, so there is nothing to gain.

One example, where it would really mess things up, may be fdisk, and I mean you really must read the warning:

# fdisk /dev/sdb Welcome to fdisk (util-linux 2.39.3). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. The device contains 'vfat' signature and it will be removed by a write command. See fdisk(8) man page and --wipe option for more details. Command (m for help): p Disk /dev/sdb: 3,78 GiB, 4055885824 bytes, 1980413 sectors Disk model: iPod Units: sectors of 1 * 2048 = 2048 bytes Sector size (logical/physical): 2048 bytes / 2048 bytes I/O size (minimum/optimal): 2048 bytes / 2048 bytes Disklabel type: dos Disk identifier: 0x6f20736b Device Boot Start End Sectors Size Id Type /dev/sdb1 778135908 1919645538 1141509631 2,1T 72 unknown /dev/sdb2 168689522 2104717761 1936028240 3,6T 65 Novell Netware 386 /dev/sdb3 1869881465 3805909656 1936028192 3,6T 79 unknown /dev/sdb4 2885681152 2885736650 55499 108,4M d unknown Partition table entries are not in disk order. Command (m for help): q 

Let me stress it:

Be sure not to hit w there! :)

When unmounted, running fsck is not dangerous:

# fsck -fvy /dev/sdb fsck from util-linux 2.39.3 fsck.fat 4.2 (2021-01-31) Checking we can access the last sector of the filesystem There are differences between boot sector and its backup. This is mostly harmless. Differences: (offset:original/backup) 65:01/00 Not automatically fixing this. Boot sector contents: System ID "MSDOS5.0" Media byte 0xf8 (hard disk) 2048 bytes per logical sector 4096 bytes per cluster 236 reserved sectors First FAT starts at byte 483328 (sector 236) 2 FATs, 32 bit entries 3952640 bytes per FAT (= 1930 sectors) Root directory start at cluster 2 (arbitrary size) Data area starts at byte 8388608 (sector 4096) 988158 data clusters (4047495168 bytes) 63 sectors/track, 255 heads 0 hidden sectors 1980413 sectors total Volume label 'UªIVATEL -' stored in root directory is not valid. Auto-removing label. Reclaiming unconnected clusters. Dirty bit is set. Fs was not properly unmounted and some data may be corrupt. Automatically removing dirty bit. Checking free cluster summary. *** Filesystem was changed *** Writing changes. /dev/sdb: 122 files, 44508/988158 clusters 

I also went on checking the system log, attaching for completeness:

My iPod supports only FAT32 as per from the following file:

where an excerpt states the file system:

Conclusion

I am disturbed and surprised at the same time, that the OP has hidden the important fact, that it is an iPod and not an ordinary USB DISK, from us. But anyway, posting this for reference, and for future readers.

I am disturbed and surprised at the same time, that the OP has hidden the important fact, that it is an iPod, or some other Apple product, and not an ordinary USB DISK, from us. But anyway, posting this for reference, and for future readers.