Hello

This Back up plus slim (inside is a ST500-LT012) used like this with root partition as sdx1, has some weird smart data in n°193 attribute : high raw value increasing rapidly and regularly when the disk is used
today 337603 > was around 1000 in last november when I began to use it (10 hours daily)

Is this a sign of a bad trend for the life of this disk ?

193 it is load/unload cycle count
I ve never seen this with other hard disks

The drive appears to have an aggressive APM setting. Examine your power management options.

_________________
A backup a day keeps DR away.

I don't know how to do this on Linux because when looking to gnome-disks APM settings for this disk, it appears as disabled, but though I can enable it if needed
Are you though considering the settings in Linux Mint Cinnamon Parameters ? "Power management" > "Suspend when inactive" is on Never

No. Look into the 'hdparm' utilities - the ones you're interested in are:

hdparm -B xxx /dev/sdX

and

hdparm -S xx /dev/sdX

This gives with sudo :
xxx: No such file or directory
and
-S: bad/missing standby-interval value (0..255)

OK I ve found a tutorial, so
- with -B > APM_level = 128 > I ve read that 128 doesn't allow the spin down
- with -S > I don't know how to get the value

Doing anything via USB is complicated. Even if you succeed in directly communicating with the HDD and changing its APM setting, it may be that the bridge firmware is also imposing its own power management regime. Also, if the OS is periodically querying the USB mass storage device, that would cause the drive to be woken up.

_________________
A backup a day keeps DR away.

To get the smart data I am allready communicating with the HDD, I had to boot on another Linux Mint with the default USB driver disabled
but I understand that it can be still limited. I ve also read that these HDD and the more recent of this type have limitation in their communication functions in themselves