Is there a way how to change the default storage level?

If not, how can I properly change the storage level wherever necessary, if my input and intermediate results do not fit into memory?

In this example:

context.wholeTextFiles(...)
    .flatMap(s -> ...)
    .flatMap(s -> ...)

Does persist() need to be called after every transformation?

 context.wholeTextFiles(...)
    .persist(StorageLevel.MEMORY_AND_DISK)
    .flatMap(s -> ...)
    .persist(StorageLevel.MEMORY_AND_DISK)
    .flatMap(s -> ...)
    .persist(StorageLevel.MEMORY_AND_DISK)

 Thanks!