Re: How to know when file data has been flushed into disk?

[Ric Wheeler <ric@emc.com>]

Douglas McNaught wrote:

> "Xin Zhao" <uszhaoxin@gmail.com> writes:
>
>  
>
> > 3. Does sys_close() have to  be blocked until all data and metadata
> > are committed? If not, sys_close() may give application an illusion
> > that the file is successfully written, which can cause the application
> > to take subsequent operation. However, data flush could be failed. In
> > this case, file system seems to mislead the application. Is this true?
> > If so, any solutions?
> >    
>
> The fsync() call is the way to make sure written data has hit the
> disk.  close() doesn't guarantee that.
>
> -Doug
>
>  
You should also make sure, if you care about data recovery after a power 
outage, that you have either disabled the write cache on your drives or 
have a working write barrier.  Without this, fsync will move the data 
from the page cache to the disk's write cache where it is up to the 
drive firmware to write it back to permanent, safe storage on the disk 
platter.

ric

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