[FATFileSystem] Disabled flush on new sector

[neilt6]

Disabled "flush on new sector" by default for a ~2.87x write performance improvement.

[neilt6]

As an example of the effect on performance, my SDFileSystem_HelloWorld program yielded an average write speed of 142.33KB/s with FLUSH_ON_NEW_SECTOR enabled, and 409.18KB/s with it disabled.

[0xc0170]

I'm not sure what the justification for having these enabled by default is, they're detrimental to write performance

I am neither. @sg- Any help here?

[adamgreen]

This feature was added and enabled in commit 2251b02. Disabling it by default would make the code work as the mbed port did originally.

[0xc0170]

cc @oliviermartin

[sg-]

from the commit message we should look at why fflush isnt/cant be retargeted.

[0xc0170]

@oliviermartin @neilt6 any more info for this changeset?

[neilt6]

Apparently _sys_ensure() was the function to override in order to retarget fflush(), but it's deprecated and no longer called by any library function. In my opinion, this will only be a concern to data logging applications where power might be removed before files are closed, in which case developers could enable automatic flushing on their own.

[oliviermartin]

I added this feature when I wrote a basic data logger with mbed.
As I said in my patch there is no easy way to retarget fflush() for mbed. Adding this feature would allow to revert this patch and write better data logger code (ie: code that invokes fflush() only when needed).

[neilt6]

Is this pull request still being considered, or should I withdraw it?