Journaling filesystems

[Jeffrey M. Vinocur]

On 28 Oct 2002, dsr+inn at mail.lns.cornell.edu wrote:

> "Jeffrey M. Vinocur" <jeff at litech.org> writes:
> > We're now running with journaling filesystems.
> 
> Which one?  Many "journaling" filesystems (including apparently most
> of the ones for Linux) only journal metadata, not data (journaling
> data can be significantly slower).

Hmm.  We're using ReiserFS 3, which indeed journals only metadata as far 
as I can tell.


> Closing the file should[1] force a synchronous update.  So should[1]
> an msync with the MS_SYNC flag.

I tried to test this, but I'm not able to make mmapped writes *not* be
visible even without any msync at all -- I don't know if the kernel is
detecting another reader and handling that "nicely" (either flushing to
disk then or reading the data out of the mmapped copy) or what.


> Use a filesystem that journals data, 

Reiser 4, some day, I guess.


> convert some of the MS_ASYNCs to MS_SYNC (may require substantial
> meditation on the code to identify the right subset of msync()s),

*mumble* *sigh*


> twiddle some of the parameters to update(8) (may have a different name
> depending on your OS) to see if you can reduce the data flush time to
> something less than 30 seconds.

It just bugs me that if the kernel is just sitting around doing nothing
(which it is), it can't be bothered to go write after a MS_ASYNC.


-- 
Jeffrey M. Vinocur
jeff at litech.org