Can anyone explain how the FlashFS handles loss of power? I am concerned about losing data that has been buffered but not written during a power failure. I will be writing directly to SPI flash chips (M25Pxx).
Also, does the file system perform wear levelling?
Many journaling FS are handling meta-data but not file data. When you have an open file and write data to it, you may not know how many bytes that will survive, and you can't modify a file in the middle and know what state it will be in if there is a power loss.
In some situations, you may have to create a new file and then replace the original file (a meta data operation) to get a snapshot change that will guarantee that you either have the old or the new file if you get a power loss during the operation.
In an embedded environment, I would be very scared to use a FS that doesn't have at least journaling of meta-data.