In the conditions where only one power supply is used to power the S5000, the cache write policy is automatically changed from write back to write through for directly writing data to disks when a power failure occurs. This mechanism improves data storage security. For redundant power supplies, fans and batteries, the S5000 is designed to automatically change the cache write policy from write back to write through when a power supply, fan, or battery becomes faulty. Given the write through policy directly writes data to disks without using the cache, the storage performance can be degraded. After the faulty power supply, fan, or battery is recovered, the cache write policy is automatically changed from write through to write back. Note that the LUN write policy always displays as the preset write back status on the Web page even after it is changed to write through for some reason.