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

[Mike Karels]

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

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.

> 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.

> 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.

		Mike

> Regards,
> Ben