zfs scrub enable by default

[John Long]

On 05/08/2020 15:24, Alan Somers wrote:
> On Wed, Aug 5, 2020 at 9:22 AM John Long via freebsd-fs 
> <freebsd-fs at freebsd.org <mailto: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

Thanks, I figured that must be the case but I thought it was better ask.

So is it correct that aside from a single disk vdev, it would be a bad 
practice to specify additional copies? How does dedup deal with it?

/jl