TrueCopy operations involve the storage systems and volumes at the primary site and secondary (remote) site, the physical communications paths between these storage systems, and the TrueCopy software. A TrueCopy system configuration consists of the following components:
- Primary and secondary storage systems
- The primary storage system contains the primary volumes and is connected to the hosts that access the primary volumes. The secondary storage system is connected to the primary storage system using the data paths. TrueCopy supports remote copy operations between various storage system models. This document provides instructions for performing TrueCopy operations.
- Main control units (MCUs) and remote control units (RCUs)
- The MCU is the control unit in the primary storage system that controls the P-VOLs of the TrueCopy pairs. The MCU communicates with the RCU through the dedicated remote copy connections. The MCU controls the host I/O operations to the P-VOLs as well as the TrueCopy remote copy operations between the P-VOLs and S-VOLs. The MCU also manages the TrueCopy pair status and configuration information.
- The RCU is the control unit in the secondary storage system that controls the S-VOLs of the TrueCopy pairs. The RCU assists in managing the TrueCopy pair status and configuration (for example, rejects write I/Os to S-VOLs). The RCU executes the remote copy operations issued by the MCU. The RCUs should be attached to a host system to allow sense information to be reported in case of a problem with a secondary volume or remote storage system and to provide disaster recovery capabilities.
- Hosts
- The hosts at the primary site are connected to the primary storage system. Hosts at the secondary site are connected to the secondary storage system for use in disaster recovery operations. If it is not possible to have hosts at the secondary site, the host at the primary site must be in communication with the secondary system for disaster recovery operations.
- Volumes
- The primary volumes (P-VOLs) on the primary storage system are copied to the secondary volumes (S-VOLs) on the secondary system. The P‑VOLs contain the original data, and the S‑VOLs are the mirrored volumes that contain the backup or duplicate data. During normal TrueCopy operations, the P‑VOL remains available to all hosts at all times for read and write I/O operations and the secondary storage system rejects all host-requested write I/Os for the S‑VOLs. The S‑VOL write enable option allows write access to an S‑VOL while the pair is split, and the S‑VOL and P‑VOL differential data is used to resynchronize the pair.
- Data paths
- Dedicated data paths, also called remote copy connections, are used for data transfer between the primary and secondary storage systems connected by a Fibre Channel or iSCSI interface.
- To establish iSCSI connections between the storage systems, make sure to use ports on the 10-Gbps iSCSI channel board. The 25-Gbps iSCSI channel board cannot be used for iSCSI connections between the storage systems.
- You should establish at least two independent remote copy connections (one per cluster) between each MCU and RCU to provide hardware redundancy for this critical communications path.
- Ports for host connection:
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- Fibre Channel interface port
- iSCSI interface port
- NVMe over Fibre Channel (NVMe-oF) interface port
- For details about the storage systems and DKCMAIN microcode versions that support the NVMe-oF interface, see System requirements and specifications.
- Hitachi TrueCopy® software
- The TrueCopy software must be installed on both the primary and secondary storage systems and is used to perform TrueCopy configuration and pair operations.
- CCI
- The Command Control Interface (CCI) command-line interface software can also be used for TrueCopy configuration and pair operations as well as disaster recovery operations.
The following figure shows a typical TrueCopy environment.