UFS2 with Soft Updates Robust?

[Erik Trulsson]

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.


> If so what options does
> one have? 

If UFS2 + softupdates + decent hardware is not sufficiently robust for
you there is little else you can do. (Unless you take Chuck Swiger's
advice above and mount the filesystem synchronously and turn off
the writecache which should give a slight increase in robustness at the
cost of a huge drop in write-performance.)

> 
> I've read that softupdates should be turned on. How much of a
> performance loss will I see if I turn softupates off?

Depends. For read performance you should not see any difference.
For write performance it will depend both on your hardware and how much
load you put on the disks.


-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at student.uu.se