Fstrim cannot trim SSD that smartctl says supports TRIM operations?

ARM
3

Sure! Thanks, @leledumbo . I also got some additional info from hdparm.

~]$ sudo hdparm -I /dev/sda | grep -i "TRIM"
           *    Data Set Management TRIM supported (limit 8 blocks)
           *    Deterministic read ZEROs after TRIM

~]$ lsblk -D
NAME   DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
sda           0        0B       0B         0
├─sda1        0        0B       0B         0
└─sda2        0        0B       0B         0
zram0         0        4K       2T         0