I've been trying to diagnose why my sites have been sporadically slow for the past week or so, and think I've finally narrowed it down to the dataglob my files are on -- '.playstation'.
Sometimes Linux file system shell commands (cd, ls, etc.) are horribly slow to respond when I'm dealing with files/directories on .playstation. I don't think it is a problem with the web server I'm on, since they moved me from 'zorg' to 'ultima' and it made no difference.
I wrote a Ruby script to test file system speed by creating/deleting 50 empty directories, and have had the script running for the past several days, performing the test once every minute. Normally it takes just a second or two, but in some cases it has taken over 1000 seconds! Take a look at the results:
As you can see, there are multi-hour periods of normalcy, but also horrible spikes where the system is practically unusable.
Whenever I run the script on /tmp (which I assume is the web server's local hard drive), it is always fast.
As an additional test, I moved one of my phpBB forum's files onto a different dataglob ('.pammy') by creating a new user, and it has been consistently fast ever since (fingers crossed).
DreamHost customer support has been trying to help me, but they won't even really acknowledge the problem; they just keep saying "intermittent issues are tough to troubleshoot" or something like that.
I'm glad I've found a way to move my sensitive files to a different dataglob (which apparently does not currently suffer this problem), but that is less than an ideal solution...