A data processing method and apparatus, and a shared storage device, where the method includes receiving, by a shared storage device, a copy-on-write request sent by another storage device, where the copy-on-write request includes data on which copy-on-write is to be performed and a logical unit identifier and snapshot time point of the data; storing the data; and searching, according to the logical unit identifier and snapshot time point of the data, a preset shared mapping table for a corresponding entry, and storing, in the corresponding entry, mapping entry information of the data, where the mapping entry information includes the logical unit identifier and snapshot time point of the data and a storage address that is of the data and in the shared storage device, which can improve efficiency of snapshot data processing.