Minimum memory for ZFS (was Re: svn commit: r356758 - in head/usr.sbin/bsdinstall: . scripts)

[Rodney W. Grimes]

> I took the liberty of changing the subject line to make it stand out a
> bit more.

Thanks, good idea, I seem to have missed some of this thread.

> Ben wrote:
> 
> > On Sat, 18 Jan 2020 at 09:16, Mike Karels <mike at karels.net> wrote:
> 
> > > > On Fri, 17 Jan 2020 at 08:21, Ben Woods <woodsb02 at gmail.com> wrote:
> > >
> > > > > Perhaps we could simply include a message on that bsdinstall
> > > partitioning
> > > > > mode selection screen that UFS is recommended on systems with < 4 Gb
> > > RAM?
> > > > >
> > >
> > > > I have uploaded a diff for this here: https://reviews.freebsd.org/D23224
> > >
> > > > Please let me know your thoughts (comments in the phabricator review
> > > would
> > > > be best).
> > >
> > > I think this needs more discussion, preferably on this list.  I am not
> > > convinced that systems with as little as 4 GB should use ZFS.  Conventional
> > > wisdom on the FreeNAS mailing list says that 8 GB is required for ZFS,
> > > and FreeNAS no longer includes UFS as an option.  Conrad suggested a
> > > cutoff of 16 GB; I am happier with 16 GB than 4 GB as a cutoff.  Also,
> > > there was mention of auto-tuning for smaller systems; I don't think that
> > > has materialized yet.  I'm not sure how plausible that is without knowing
> > > the workload.  I use ZFS on a workstation/server with 64 GB that runs 4
> > > bhyve guests that do things like buildworld.  ZFS wants 63 GB for arc_max;
> > > needless to say, I have a tunable set to a much lower value.  If tuning
> > > is required, it is unclear that ZFS is a good default.
> > >
> > >                 Mike
> > >
> 
> 
> > Hi everyone,
> 
> > Before I commit phabricator review D23224, is there any final comments?
> 
> > Particularly on these 2 lines of help-text:
> > msg_partitioning_zfs_help="ZFS is recommended if you have at least 4GB RAM"
> > msg_partitioning_ufs_help="UFS is recommended if you have less than 4GB of
> > RAM"
> 
> > There is some disagree about what these 2 recommendations should be.

ZFS is recommended if you have read the ZFS memory tuning guide :-)
I have run it in some pretty tiny memory configurations, with proper
tunning including 32bit nodes with 512MB of memory and no other memory
intense processes.

> > 4GB was recommended by: imp, emaste, philip, eugen, dteske
> > 8GB was recommended by: mike
> > 16GB was recommended by: cem
> 
> > The 4GB limit seems to have the best consensus, however there was some
> > debate about whether ZFS is recommended on a system with 4GB, or only
> > systems with MORE THAN 4GB.
> 
> I don't remember what everyone else wrote, but IIRC, Devin said that if
> you use ZFS with 4 GB, you will soon end up with a dozen tunables set.
> That doesn't sound like a recommendation for 4 GB.

>From my perspective ZFS is a great thing, BUTT in no case where I have
it installed is it running with out of the box settings.  In all cases
I minimally tweak vfs.zfs.arc_max as the default for this leaves systems
with a configuratoin that invariable runs into OOM issues.

Until that issue is fixed for me it is a mistake to make ZFS default
on any system, no matter how much memory it has.

> 
> > As for the ZFS auto-tuning, I see that as being a separate discussion
> > (which could ultimately change this recommendation, but shouldn't prevent
> > us from committing this help text now).
> 
> Agreed, but the lack of tuning should factor into the current recommendation.

And I agree with Mike here, these tuning issues defanitly should affect
our choices of default install recomendations.

> 		Mike
> 
> > Regards,
> > Ben
-- 
Rod Grimes                                                 rgrimes at freebsd.org