zfs scrub enable by default

[Alan Somers]

On Wed, Aug 5, 2020 at 9:22 AM John Long via freebsd-fs <
freebsd-fs at freebsd.org> wrote:

> On 05/08/2020 13:15, Bob Friesenhahn wrote:
> > On Tue, 4 Aug 2020, Karl Denninger wrote:
> >
> >> Let me give you two allegedly "degenerate" cases that are actually not
> >> degenerate at all.
> >>
> >> 1. A laptop or workstation.  It is backed up.  It uses ZFS because
> >> it's faster, and I can establish a filesystem for some project very
> >> easily and quickly, it's segregated, I can work on it and destroy it
> >> trivially when done.  I can set quotas on that, etc.  If I want to
> >> move its mountpoint, I can trivially do so. And so on.  Note that here
> >> there is no redundancy at all; no raidZx, no mirroring, etc.  I'm
> >> merely using it for convenience.
> >
> > Did you remember to set copies=2 or copies=3 for zfs filesystems where
> > you hope not to experience data loss?  It needs to be set as soon as
> > possible since it only applies to new files.  This is a way to get more
> > media redundancy, although the whole drive may fail.
>
> Does copies=n actually create n-1 additional physical copies or is it
> copy-on-write, or something else yet?
>
> /jl
>

Yes, copies=3 will actually create 3 physical copies of the data
somewhere.  It's basically mirroring at the DMU layer, rather than the
block layer.
-Alan