All-flash array storage system, Hitachi Virtual Storage Platform F600, is modular and rack-mountable. Dual controllers are in the storage systems to facilitate communication with a data host. Each controller has a processor, batteries, fans, and dual in-line cache memory modules (DIMMs). For out-of-band management, each controller also has an Ethernet connection. All hard discs are still accessible to data hosts via a redundant data way through the other controller if the data path through one controller fails. Controllers for storage systems can be changed. Network-attached storage (NAS) modules can be added to the storage system. In addition to the block access offered directly by iSCSI and Fibre Channel I/O modules, the NAS modules also offer file access through CIFS and NFS protocols and block access through iSCSI protocols. All types of storage systems enable the replacement of bad drives without affecting host computers' access to data. The fault-tolerant integrity of the logical industry can be protected by configuring a spare hot drive to replace a failing drive automatically. Hardly-based and self-contained, RAID logical drives offer the best performance in small external enclosures.