Re: Proposal to enable WAPBL by default for 10.0

[maya%NetBSD.org@localhost]

On Thu, Jul 23, 2020 at 08:56:14PM +0000, David Holland wrote:
> On Thu, Jul 23, 2020 at 07:45:08AM +0200, Micha? G?rny wrote:
>  > > > Rationale: the default filesystem (FFS) without WAPBL is more prone to
>  > > > data loss.
>  > > 
>  > > It is not, unfortunately. We had WAPBL on by default some time back
>  > > and eventually switched it off.
>  > > 
>  > > The problem is that because it still doesn't do anything about
>  > > journaling or preserving file contents, but runs a lot faster, it
>  > > loses more data when interrupted.
>  > 
>  > How does that compare to the level of damage non-journaled FFS takes?
> 
> To be explicit:
> 
> It is the same underly problem either way, and it is worse in practice
> with WAPBL than without because WAPBL ffs runs faster than non-WAPBL
> ffs and thus accumulates more unwritten blocks.

It looks like this difference is because FFS doesn't flush the disk
cache often, but if WAPBL is enabled, it does on every log write.