Suppose I have a "green" USB hard drive that frequently spins down the drive in order to save energy, then spins back up when a file system mounted on it is accessed. It is mounted at /var/backups.
I'm logged in as a non-root user with my home directory as my current working directory. The file system containing my home directory is mounted at /home. I'm using a shell prompt via a graphical terminal emulator (xfce4-terminal, in my case). Now, I enter an 'ls' command at a bash prompt. The output doesn't appear until after my USB hard drive spins up. Note that neither /var/backups nor any directory under it is in my shell's PATH, nor is there any symlink to /var/backups in my current working directory. Thus, there should be no need to read /var/backups, yet evidently this exactly what happens.
Question: why does a sleeping hard drive that has no connection with the file system I'm working with have to spin up? The behavior I would expect is that the hard drive would spin down after its file system(s) have not been accessed for a certain amount of time and would spin up if/when a file system on it is accessed. If I'd entered 'ls /var/backups' or 'cd /var/backups' or even a command that accesses all file systems (e.g., 'df') I'd totally expect the hard drive to spin up, but I don't get at all why it should spin up if I'm not accessing any data on it.
I don't like this behavior for two reasons: (1) unnecessary I/O delays while waiting for a hard drive that I'm not explicitly accessing to spin up, plus (2) unnecessary wear and tear on the "green" hard drive.
Other than keeping all of my hard drives spinning all the time--i.e., by using a non-green hard drive in my USB enclosure--is there any way to prevent this behavior? What might be causing it?
Thanks, Dave