There are many partitions on that drive. To know which partition you should be looking at, I need to know what version of mycloud you have (Gen1, or Gen2). Gen1 has a firmware that says 4.xxxx for the version. Gen2 has a firmware that says 2.xxxx for the version.
From the data recovery software thread, Gen2 myclouds have the data volume on partition 2.
Bennor says that on Gen1 it is partition 4.
For the manual mount under linux, on Gen2 it would be
sudo mount -t ext4 /dev/sdb2 /some_mount_point
and on gen1 it would be:
sudo mount -t ext4 /dev/sdb4 /some_mount_point
The data recovery thread can be found here:
