dangerous situation with shutdown process

[John-Mark Gurney]

Matthias Buelow wrote this message on Thu, Jul 14, 2005 at 21:52 +0200:
> >The problem is that disks lie about whether they have actually written
> >data. If the power goes off before the data is in cache, it's lost.
> 
> No, the problem is that FreeBSD doesn't implement request barriers
> and that softupdates is flawed by design and seemingly could not
> make use of them, even if they were available (because, as I
> understand it, it relies on a total ordering of all writes, unlike
> the partial ordering necessary for a journalled fs).

even request barries will not save the fs in a power loss if the track
that is getting flushed durning a power loss...  Some other FreeBSD
folk has a reproducable case of where blocks that were not written to
on ATA hardware got trashed after a power loss...

With non-written to sectors getting trashed with the cache enabled,
barriers don't mean squat...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."