I have a nominal 500 GB SSD with one ext4 partition which is used for the OS (UM 20.04) and all other files. The partition was created by the install process when the disk was brand new some years ago.
System monitor reports as follows: about 491 GB total, with 368 GB used.
The disks utility reports 123 GB free. SMART data all look OK.
Caja reports the following regarding the root (only) file system. Used = about 190 GB, free/available about 98 GB.
So, it looks to me as if there is about (500 – 190 – 98) = 212 GB being used in an undefined way according to the caja values. If you use the larger amount of free/available space from the disks utility, the amount of undefined space is about 187 GB, surprisingly close to the size of root (/). It seems almost as if / is being mirrored on the ssd.
I am puzzled by the large apparently hidden space, which is not available for me to use. If possible, I would like to make it available. I would love for someone to help me to understand the values. Probably this is all about educating me, so I appreciate your indulgence.