zfs scrub enable by default

[Steve Wills]

Hi,

On 8/4/20 11:54 AM, Matthew Ahrens wrote:
> This question was raised elsewhere, and I agree with this reply from 
> George Wilson, my colleague and an expert in the i/o subsystems of ZFS 
> as well as having lots of experience with customers:
> 
>     Having scrubs enabled by default is a great idea but at Sun (and
>     Delphix too) we found that the impact was often too much for some
>     workloads/customers. This is the challenge we faced and why there
>     was never a policy to enable it everywhere. We did explore ideas to
>     make the impact less and to be able to always scrub. Some of those
>     ideas included periodic or continuous scrubs where the impact could
>     be reduced by only scrubbing portions of the pool at a time, at a
>     reduced i/o rate. At Delphix, we have investigated similar concepts
>     and one of our interns prototyped one of the ideas.Much has changed
>     since the early scrub days and revisiting some of the earlier ideas
>     and investigating new ones is probably a good topic for the
>     community. I do think that just enabling scrub by default without
>     further enhancements would still be too impactful for some customers
>     but the concept definitely has merit.
> 

Thanks for that! Very informative. I thought the Fishworks storage 
appliances had it on by default, but maybe I'm mistaken or maybe it 
changed over time.

I wonder what "some" means, that is, is it 80% of people? 50%? 20? And 
what percent would mean "too many" to have it on and expect them to tune 
it if needed. I suppose there's no way to know.

There are definitely some interesting ideas for how to limit the impact 
of scrub, but those would definitely have to be built and proven, of course.

Thanks again, really helpful!

Steve