Although the majority of Mavericks related data loss problems seem to be limited to Promise and Western Digital external storage devices, there are a growing number of people that have reported similar experiences with other USB/FireWire external drives. Many LaCie and Seagate drives in particular have been reported to stop working after upgrading Mavericks.
This is likely related to very old firmware on the drives, or the drive was formatted with a vendor supplied utility instead of Apple’s Disk Utility.
Because of this potential data loss issue, if you use one or more external drives with your Mac, I would recommend that all critical externally stored data is backed up to a redundant source prior to considering the upgrade to Mavericks. Also I would highly recommend that you download the latest firmware utilities for your external drives, and check each drive to verify it’s running the latest firmware. This has always been All Covered’s Chicago best practice prior to any major OS upgrade, but is very easily overlooked.