A synchronization system synchronizes objects between a portable computer and a desktop computer. The portable computer is capable of communicating with a storage volume that can become inaccessible to the portable computer. The system identifies storage volumes currently available to the portable computer and identifies storage volumes previously accessible to the portable computer, but not currently accessible to the portable computer. Objects contained in storage volumes that are currently accessible to the portable computer are then synchronized between the base computer and the portable computer. During the synchronization process, the system ignores objects stored on volumes that are not currently accessible to the portable computer. However, the system continues to monitor and record changes to objects stored on volumes that are not currently accessible to the portable computer. When a storage volume that was previously inaccessible becomes accessible, the system synchronizes objects stored on the previously inaccessible storage volume. The objects may be databases or other data structures. The storage volume that can become inaccessible to the portable computer is typically a removable memory card that can be inserted into the portable computer.