Abstract: In one aspect, a method includes selecting a C-module; sending a write from a host to the selected C-module; selecting a D-module to commit a page related to the write; selecting a R-module to transmit data from the write to the target; writing the data from the write to target location; and writing the data to an address-to-hash table after acknowledgement that the data has been written to the target location and after the D-module acknowledges that the page is committed.

Abstract: In one aspect, a method includes receiving a request to write to an offset in a first logical device, determining a second logical device that wrote to the offset, the second logical device being an ancestor of the first logical device in a hierarchical tree of snapshots, determining from decedents of the second logical device in the hierarchical tree whether data in the offset of the second logical device is shadowed data or partially shadowed data, removing address-to-hash mapping for the offset of the second logical device if the data for the offset is shadowed and moving address-to-hash mapping to a single descendent of the second logical device if the data for the offset is partially shadowed.