Collections salvage after system crash


After a system crash, MongoDB (4.0.6) refuses to start because of corrupted data. Mongod --repair does not fix it:

WT_CURSOR.search_near: read checksum error for 24576B block at offset 57344: block header checksum of 3933356853 doesn’t match expected checksum

(full log:

I try to repair with more recent tool with more effect.
I’m not able to execute a mongodump because Mongod refuses to start.

First point:
How can I restore collection?
How to retrieve data from collection files (for instance collection-101–1569900909144710.wt)?

Second point:
What is recommended for MongoDB resilience: backup, distribution?

Thanks by advance.