Changing the default for ZFS atime to off?

[Chris Ross]

  I agree strongly with Jeremy's general opinion.  But, am far less established
in the community, so only wanted to make a couple of small points.

On Jun 8, 2013, at 20:48 , "Steven Hartland" <killing at multiplay.co.uk> wrote:
> I guess where I'm coming from is making better for the vast majority.
> 
> I believe there's no point in configuring for a rare case by default
> when it will make the much more common case worse.

  I think the point being made, and certainly in my mind reading this thread,
is that you're considering the "rare" case to be more rare than you factually
know it to be, and more importantly (IMO), you're considering "worse" on
something that I consider a very small issue.  I understand the reasons we
choose to turn off atime (by adding it to the kernel, at the time, in 1994) at
UUNET for the USENET filesystems.  It was just too much activity.  But, for
a less than 110% active system, and given the relatively small number of things
that are accessed far more often than they're updated, I just don't think it's that
big of an issue.

  And, yes, I'm aware of the flash write issue, and I side with turning off there,
though I wouldn't be default.  (And, defaulting filesystem parameters based on
some impression of the underlying hardware seems risky at best anyway.)

  I think there are a small number of cases where it's an issue, and those people,
yourself included, already know how to solve the problem.  Myself, personally,
running only small systems, have never turned off atime updates.  Don't feel
any need to.  For specific heavy-load production systems, _everything_ is
looked at with a fine-toothed-comb.  No reason to "default" something that
only those systems need.

>> All said and done: I do appreciate having this discussion, particularly
>> publicly on a list.  Too many "key changes" in FreeBSD in the past few
>> years have been results of closed-door meetings of sorts (private mail
>> or in-person *con meetings), so the fact this is public is good.
> 
> Everyone has their different uses of any OS, different experience etc,
> so things like this need open discussion IMO.

  I agree very much, and while my opinions may not match many others, I've
been very pleased to read this discussion.  Thank you for bringing it up.

                                                - Chris