1. Log in to the S5300 and check the status of RAID groups and LUNs, and the mappings to server db1, including FC links and HBA status. All status is normal. Therefore, the fault is not caused by hardware problems or physical links between server db1 and the S5300. 2. Log in to server db1 and check the server status, and find that server db1 is normal. Restart server db1. The fault persists. 3. Based on previous two steps, it is suspected that the fault is caused by an UltraPath problem. A. Choose Computer Management > Device Manager > SCSI and RAID Controller to check the UltraPath software and find that it is properly installed and has the multipathing driver. B. Choose Computer Management > Device Manager > Disk Driver to check the physical disks mapped from the S5300 and find that the number of physical disks is twice as that of mapped disks but no virtual disks of the same number of mapped disks exist. C. Choose Computer Management > Device Manager > System Device and find that yellow exclamatory marks exist ahead of UltraPath devices. It is determined that the fault is caused by an UltraPath problem.