UFS2 with Soft Updates Robust?

[John Conover]

Erik Trulsson writes:
> On Wed, Dec 22, 2004 at 08:57:00PM -0900, Damien Hull wrote:
> > On Tue, 2004-12-21 at 21:31 -0500, Chuck Swiger wrote:
> > > John Conover wrote:
> > > > Is UFS2 with soft updates the most robust file system in freebsd?
> > > 
> > > No, although UFS2 with softupdates is robust enough for production use.
> > > 
> > > If you make the filesystem writes syncronous and disable write caching on the 
> > > hard drive, you will improve the robustness at significant cost to performance.
> > > 
> > 
> > Are you saying that the UFS2 file system sucks?
> 
> Not at all, but standard IDE-drives suck when it comes to robustness.
> (They tend to lie and tell the OS that data has been written to the
> disk, when in reality it has only been written to the disks cache.)
> (Thus the advice above to turn off write-caching for maximum
> robustness.)
> 
> If you use softupdates (on a disk that doesn't lie) the filesystem on
> the disk will always be consistent, but data written during the last 30
> seconds or so might not yet have been written to the disk, and can therefore
> be lost if e.g. the power to the computer is turned off.
>

Erik, does that mean if you use softupdates, (on a SCSI,) that,
although file(s) currently being written may be truncated since the
cache is not flushed, that the file system can be repaired
automatically by fsck to a consistent state?

Even without synchronous writes or enabling cache write through?

	John

BTW, the reason for the question is that most SCSIs today have many
meg of HW cache, and many, (maybe most,) controllers don't permit
write through anymore. So, even if the OS flushes its cache, the HW
cache may not be written to the disk-so synchronous writes and OS
cache write through may be of little value.

-- 

John Conover, conover at rahul.net, http://www.johncon.com/