FIX: add guard to ignore claen mb in preparing metadata

Test narrowed down.
It doesn't untar and compile Ruby

Don't merge to develop!!!

To merge
1. Understand why we resolve this problem by adding few lines
   What is the problem per se?
2. Test in more complicated recovery case

Also,
removed TRIM lines after migrated.
The blocks discarded will be read in dirty data replay in recovery path.
Since the buffer size is 512KB enough big for block size in SSD
we don't need to discard the data blocks.
If we delete these lines, the performance won't change actually.