The command_storage_<namespace>.dat files are GZip'd NBT files located in the data folder in a savegame. They store information about the /data command storage in the world. Each namespace in the storage has its own data file.
/data
Multiple command_storage_<namespace>.dat files may be present in the data directory.
command_storage_<namespace>.dat
data
<namespace>:<name>
/execute store
Muitiple compound tags of different names may exist under contents tag.