I recently upgraded to Ubuntu 16.04 after which my external USB drive will not mount. I'm new to this and am in fear of losing the data.This is the error msg.
Error mounting system-managed device /dev/sdd1: Command-line `mount "/mnt/wwn-0x5000039ff4d96d08-part1"' exited with non-zero exit status 32: mount: /dev/sdd1 is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on /dev/sdd1,
missing codepage or helper program, or other error

This from blkid
Disk /dev/sdd: 2.7 TiB, 3000592982016 bytes, 732566646 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x40a863e7

Device Boot Start End Sectors Size Id Type
/dev/sdd1 * 0 2955679 2955680 11.3G 0 Empty
/dev/sdd2 2927216 2931951 4736 18.5M ef EFI (FAT-12/16/32)
jucick@Home:~$ sudo blkid
/dev/sda1: UUID="d2165b35-009f-454c-87c3-9587c62b6a9f" TYPE="ext4" PARTUUID="00049b98-01"
/dev/sda2: UUID="7b8eea06-fec0-4047-9e0c-7741be004718" TYPE="swap" PARTUUID="00049b98-02"
/dev/sda3: UUID="cde4346b-22e5-4b20-a236-dc100f48497d" TYPE="ext4" PARTUUID="00049b98-03"
/dev/sdb1: LABEL="Secondary" UUID="401183b3-1ff3-4dbc-8952-8668809dba36" TYPE="ext4" PARTUUID="3cf24fc8-d146-466a-a901-870d220b102b"
/dev/sdd1: UUID="2016-07-19-21-27-51-00" LABEL="Ubuntu 16.04.1 LTS amd64" TYPE="iso9660" PTUUID="40a863e7" PTTYPE="dos" PARTUUID="40a863e7-01"
/dev/sdd2: PARTUUID="40a863e7-02"

How did you do the upgrade ?. Did you happen to download an iso and write it to a USB ?. Looks like it ...

I via a pop up notifying me it was available. It was all automated from there on. Did not dl any ISO, or should I say manually.

What does your /etc/fstab look like?

Also, it kind of looks like you may have an install iso over the hard drive.

I think Cardinal548 may be seeing the same thing:

/etc/fstab this command not working for me, I've likely not got it correct, what is it in full?
tks

to see the file open up terminal and use the following. It will work as long as nano is installed:

You may need to use sudo, but it's best you don't so you don't change values by accident.

This basically shows you how your drives are mounted at boot.

There is no need to open fstab with an editor, you can print it to the screen with cat command or use a pager like less to view it. Anyhow, it sure looks like there is an ISO written to the sdd1. Time to restore your sdd from backup.