[lug] question about ext 2/3 fs

[D. Stimits]

...

>I rebooted my machine and all the frational seconds digits got set to
>zero on my test files, so your surmise that these are not stored on
>disk certainly has a lot of explanatory power.
>
>But these digits mess up my attempts to test a backup system. Does
>anyone know of a way to clear them out of the OS that is faster than
>rebooting?  Is there a system call, or better yet, a command line
>utility? (sync doesn't clear internal OS mtime data)
>  
>

Yet another guess...the file system caches via a buffer layer in ram (if 
not for this, you wouldn't need journaling). Perhaps something modified 
through the buffer hold the extra resolution, despite not writing all of 
this to disk. An experiment to test this would be to mount a disk or 
loopback file that has been formatted -o sync, to disable caching, and 
force synchronous writes. Compare file modification time behavior both 
-o sync, and without this. Could be that synchronous writes will do the 
trick for you.

D. Stimits, stimits AT comcast DOT net