If using SD file system you need a esp-idf newer than 2.1

[perryc]

Been using esp-idf 2.1 for the last month and thought all was well until I started to come across files had missing or repeated bytes at locations that were a multiple of 512 when writing to a sd card. Found that fwrite() on a file that already had data that was not aligned to 4 bytes, a large fwrite would return the correct number of bytes written but would add or subtract a few bytes at locations that were a multiple of 512. Looks like a July 31/17 push fixes this. Looked at a lot of upstream code before I suspected fwrite was broken, hope this saves someone some time.

Perry