Storage system, memory management method, and management node

A method of operating a storage system, wherein the storage system includes a management node and multiple storage nodes, each of the multiple storage nodes includes a first storage device of a first type and a second storage device of a second type, a performance level of the first storage device is higher than a performance level of the second storage device, the first storage device includes a dynamic random access memory (DRAM), and the second storage device includes a storage class memory (SCM), the method comprising:

• creating, by the management node, a globe cache comprising the first storage device and the second storage device in each storage node, wherein the memory pool includes a first tier comprising the first storage device in each storage node, and a second tier comprising the second storage device in each storage node, wherein the first tier is configured for storing data with a high access frequency, and the second tier is configured for storing data with a low access frequency, wherein both the first storage device and the second storage device in the globe cache have memory interfaces, and are configured to be directly accessed by a processor of each storage device through a memory bus;
• monitor, by the management node, an access frequency of target data in the first tier, wherein the target data is located in the first storage device of a first storage node in the multiple storage nodes;
• and
• instruct, by the management node, the first storage node to migrate the target data from the first tier to the second tier within the globe cache, when the access frequency of the target data is lower than a threshold.