https://wiki.debian.org/InstallingDebianOn/Seagate/PersonalCloud

Have a perfectly fine Network Access Storage (NAS) drive that stopped getting official support a few years ago. Found out there is Open Source Software support for it, which basically meant i had to install a custom bootloader, wipe the drive and install debian via Secure Shell (SSH).

Was head scratching past few days as it was powering off the HDD / not responding to network ping, and what they don't mention in the wiki is that there's a command you can run from shell to disable it.

root@debian:~# hdparm -S 0 /dev/sda

/dev/sda:
setting standby to 0 (off)

root@debian:~# hdparm -B 255 /dev/sda
/dev/sda:
setting Advanced Power Management level to disabled
APM_level = off

You might also find it hard to push the files through (should be almost instant if good, otherwise it will slowly time out) unless you are running 'clunc' via sudo (if tftpd is running as sudo too; that is, has to be same user or adjust file permissions) - apart from these two caveats, it was pretty simple but YMMV.

Edit: i got access to the wiki and added the standy/ APM caveat on there. Not sure if it glues on reboot but i added both commands in /etc/rc.local