MSSN stands for Missing Shutdown Sequence Number. This is a value stored in the root block of the LSS. It equals the number of times that the store has not been gracefully shutdown over its life. This is zero if the store has always been properly closed (so that the store is check pointed and flushed correctly). A large value indicates that there have been many power failures or the client software is not closing the LSS correctly.
The MSSN is useful for correctly mapping Seids to a larger global address space that encompasses objects stored on many computers. Single user applications of the LSS have no need for the MSSN other than a simple diagnostic.
When the store is first created the MSSN is initialised to zero. The value persists and is only incremented during recovery if it is found that the store wasn't previously shut down gracefully.