External hard drive seems to block applications randomly

Solution 1:

It might be the Spotlight indexing. Do you see mdworker active in Activity Monitor when this happens? If you have not done this yet, you might try excluding the drive in the Spotlight Privacy settings in System Preferences and see if that helps.

Solution 2:

Sounds like it's Time Machine doing it's scheduled backup, it would slow down your current process as it checks your home folder for changes.

Solution 3:

I would say that the external drive has it's own internal power management that is causing the disk to spin down. With some effort you could write a script that writes a file to the external drive, deletes it and then repeats every minute.

If you have any apps on the external drive, and especially an app that once registered a service, then I suspect your external drive is spinning up on a right click in order to help build the services menu. Or it could simply be that Plex itself is choosing to scan the external drive.

I'd research your external drive a bit and see if it spins down the disk on its own and then how to prevent it from happening.

This script

 #!/bin/bash
 # Used to not let a volume named MYBOOK sleep

 volpresent=$(mount | grep MYBOOK | wc -c)

 if [ $volpresent -gt 0 ]
 then
    touch /Volumes/MYBOOK/.hiddenfile
 fi

Comes from this hint http://hints.macworld.com/article.php?story=20090316190817357