Note: This article applies to Mac OS X 10.2 or later and Mac OS X Server 10.2 and later. Occasionally, Disk Utility may report that a software mirror has become degraded and that it must be rebuilt. In such a situation, one drive has become out of sync with another. To rebuild the software mirror, follow these steps below. Warning: Before proceeding, you must back up of all data, because failure to follow the steps correctly may result in data loss.