Why Won't My Hard Drive Mount?

Question

I have a hard drive that used to be an external hard drive on a Windows machine. It has since been extracted and is installed in my ubuntu machine as /deve/sda.

Before I reformat or repartition it, I want to mount it to see what's currently on it.

This is what I get when I run lsblk -f /dev/sda:

NAME   FSTYPE LABEL UUID FSAVAIL FSUSE% MOUNTPOINT
sda
└─sda1

And this is what I get from fdisk -l /dev/sda:

Disk /dev/sda: 3.65 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: WDC WD40EZRX-00S
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0xdb4bf07b
Device     Boot Start       End   Sectors   Size Id Type
/dev/sda1         256 976746239 976745984 465.8G  7 HPFS/NTFS/exFAT

I notice that it only has one partition, which is 10% the size of the whole disk. I have no idea what might cause that.

I have created the directory /mnt/a.

When I try to mount the partition with the command command sudo mount /dev/sda1 /mnt/a, I get the error

FUSE exfat 1.3.0
ERROR: exFAT file system is not found.

I get the same message for the following commands:

• sudo mount /dev/sda /mnt/a
• sudo mount -t exfat /dev/sda1 /mnt/a
• sudo mount -t exfat /dev/sda /mnt/a

Am I doing anything wrong with the mount command? Is there something wrong with the disk / partition?