which directory is the best for mounting  usb hdd

under /media or  /tmp ?

my understanding /tmp is mounted to memory while /media is mounted to sdcard

which mean when mounting to /media then can reduce life time of sdcard while often writing

am i understanding correctly?

If you create directory for mounting in /tmp and add an entry to fstab, then after reboot your directory in /tmp will not be there and your fstab entry will be incorrect.

 

If you create directory on SD (i.e. in /media or /mnt), as long as your HDD is mounted, writing to HDD won't produce writes to SD card.

 

"mounting" operation itself may update access time on directory (which results in small write to SD) but in Armbian rootfs is mounted with "noatime,nodiratime" options, so it won't try to update access time in this case.