Compressing metadata blocks prior to writing the metadata blocks out to secondary storage

A technique manages file system metadata and is performed in a data storage system that maintains a file system on behalf of a set of host computers. The technique involves modifying a first metadata block of the file system in response to a file system change, the first metadata block containing file system metadata. The technique further involves performing a compression operation to generate a compressed metadata block in volatile storage from the first metadata block, the compressed metadata block having a size that is smaller than a size of the first metadata block. The technique further involves writing the compressed metadata block from the volatile storage (volatile cache memory) to non-volatile storage (e.g., flash memory).