A colleague purchased two Iomega 500GB eGo portable hard drives at the Apple Store to use with his new MacBook Pro 15″.  He set up one drive to be a Time Machine backup drive (Backup) and the other as external data storage (Datastore).  The problem was whenever he plugged in Datastore the MacBook Pro treated it like Backup and would proceed to backup to Datastore – the incorrect disk.  I tried some draconian methods – deleting the .com.apple.timemachine.support, .fseventsd, and the sparsebundle, but Time Machine kept using Datastore every time I plugged it in.  This is in addition to Time Machine using Backup every time it was plugged in.

I fixed the problem by deleting the partition with Disk Utility and recreating the disk partition.  I believe Iomega has made a mistake in the way they make this product the “Mac Edition”.  My theory is they are imaging the drive with the same blank image.  This image contains the token Time Machine uses to identify “what drive is this?” (Time Machine doesn’t use volume name).  This results in Time Machine seeing every drive in this product line as the same drive.  When you make a new partition, the drive’s identity token is deleted and a new one created – problem solved.

Details

• Iomega 500GB eGo FireWire/USB 2.0 Portable Hard Drive, Mac Edition
• Apple’s web site says “Mfr. Part No.: 34629” but the underside of the unit says Model No: RPHD-TG.
• Mac OS X 10.5.8
• Iomega creates the partition with Apple Partition Map.  When I recreated the partition I used GUID Partition Table
• The USB Serial Number as shown in Disk Utility was different for each drive when plugged in so this isn’t the token.
• These units also can connect via Firewire 800 which we were doing.  Firewire devices have a Connect ID in Disk Utility.
• Having one drive plugged in via Firewire and one plugged in via USB had no affect on this problem – it failed just the same.