I was running into a problem where non-IDE drives would not mount at startup until a user logged in at the GUI. In an all-SCSI system, this meant that I couldn't ssh into the machine and access my volumes (outside of /), and startup scripts that required a separate volume (like moving swap to a different partition/disk) wouldn't run. A solution is to create a file at /Library -> Preferences -> SystemConfiguration -> autodiskmount.plist, with contents:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>AutomountDisksWithoutUserLogin</key><true/>
</dict>
</plist>
NOTE: The !DOCTYPE entry is shown on two lines; enter it as one with a space between the sets of quotes.
Mac OS X Hints
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