A method includes generating a map for a storage tier. The map maps a plurality of extents to physical locations on the storage tier and is implemented as a tree with each extent to physical location mapping being one of a plurality of leaf extent nodes of the tree. Individual ones of the plurality of leaf extent nodes are compressed into small extent nodes. Different groups of the small extent nodes are associated with carrier nodes. A command that involves an extent of the plurality of extents, which is represented by a small extent node in one of the carrier nodes, is received from a host. A decompression operation is performed on the small extent node in the carrier node to provide a leaf extent node for the extent associated with the host command. An extent node operation is performed on the leaf extent node for the extent.