The HA solution uses the HyperMetro technology of storage devices to implement DR protection.
The data dual-write and DCL mechanisms are used to implement HyperMetro data at the storage layer.
- Dual-write is a process in which I/O requests of an application server are synchronously written to both the local and remote LUNs.
- DCLs record data changes in the storage systems of the two data centers.
- Write I/O process:
Efficient lock allocation and data dual-write mechanisms are the core for implementing HyperMetro between two storage devices. Data changes can be synchronized using the dual-write and DCL technologies while services are running, ensuring data consistency between two data centers.
Two storage systems with HyperMetro enabled can process host I/O requests concurrently. The locking mechanism is used to prevent access conflicts that occur when different hosts concurrently access the same storage system. Data can be written into a storage system only after the storage system is granted by the locking mechanism. If a storage system is not granted by the locking mechanism, the storage system must wait until the previous I/O is complete and then obtains the write permission after the previous storage system is released by the locking mechanism.
- Dual-write enables the I/O requests sent from application servers to be delivered to both local and remote caches, ensuring data consistency between the caches.
- If one data center fails, DCL records data changes in the other data center. After the storage system recovers, the data changes are synchronized to the storage system, ensuring data consistency across DCs.
Figure 1 shows the HyperMetro write I/O process when an application server delivers an I/O request that causes data changes.1. An application host delivers a write I/O to HyperMetro.
2. A log is recorded.
3. HyperMetro concurrently writes the write I/O to both the local cache and remote cache.
4. The local cache and remote cache return the write I/O result to HyperMetro.
5. A storage array returns the write I/O result to the application host after receiving the feedback from the local cache and remote cache.
6. The storage array determines whether dual-write succeeds.- If the write I/O request is processed successfully, the log is deleted.
- If the write I/O fails to be written to the local cache or remote cache, the log is converted into a DCL. The DCL records the differential data between the local LUN and remote LUN.
If writing to either cache fails, HyperMetro is suspended and each storage system sends a quorum request to the cloud platform quorum server. The winning storage system continues providing services while the other stops. The storage system uses DCL to synchronize data in the background. After the data on the local LUN is the same as that on the remote LUN, HyperMetro services are restored.
- Read I/O process:
Data on the LUNs at the two ends are synchronized in real time, and hosts can read and write LUNs at both ends. If the storage array in one data center malfunctions, the storage array in the other data center takes over host services.
Only Huawei UltraPath can be used in the HyperMetro solution. Huawei UltraPath has the region-based access optimization capability, reducing the number of interactions between sites. UltraPath can read data from the local or remote storage system. However, when the local storage system is running properly, UltraPath preferentially reads data from the local storage system, preventing hosts from reading data across data centers. UltraPath can read data from the local or remote storage array. However, if the local storage array is working properly, UltraPath preferentially reads data from the local storage array, preventing data read across data centers.
Figure 2 shows the read I/O process.
1. An application host applies for the read permission from HyperMetro. If the link between the storage arrays in the two data centers is down, the cloud platform quorum server determines which storage array continues providing services for hosts.
2. HyperMetro enables the local storage array to respond to the read I/O request of the host.
3. HyperMetro reads data from the local storage array.- If the local storage array is working properly, it returns data to HyperMetro.
- If the local storage array is working improperly, HyperMetro enables the host to read data from the remote storage array. The remote storage array returns data to HyperMetro.
4. The read I/O request of the host is processed successfully. If the data of one storage array is abnormal, HyperMetro uses data on the other storage array to repair the data, ensuring data consistency between the two data centers.
