mongodb wt file corrupt issue, can not query few documents
Ok we "fixed" the issue or atleast solved the problem of Mongo crashing

The wt collection file was corrupt and was not readable. 
We run ddrescue and got rid of the bad sections in the file 

ddrescue -n -e1 /database/mongocluster/shard2/b0/collection-72--3831537583791950739.wt RecoveredFiles/collection-72--3831537583791950739.wt RecoveredFiles/collection-72--3831537583791950739.wt.log


And then run wt to salvage the file

./wt  -v -h /database/mongocluster/shard2/b0 -C "extensions=[./ext/compressors/snappy/.libs/libwiredtiger_snappy.so]" -R salvage collection-72--3831537583791950739.wt


Thats it!!. The bad documents could not be recovered, but never mind I can regenerate that data from my app. Most importantly the mongo server does not crash. Hopefully mongodb will improve the logic in the newer versions. Crashing the db on any single I/O error is not very helpful