Re: Set ZFS pool ashift=14 for FreeBSD root pools?

On Tue, May 12, 2026 at 9:45 AM Lionel Cons <[email protected]> wrote:
>
> On Tue, 12 May 2026 at 17:36, Alan Somers <[email protected]> wrote:
> >
> > On Tue, May 12, 2026 at 8:46 AM Lionel Cons <[email protected]> wrote:
> > >
> > > On Tue, 12 May 2026 at 12:51, vermaden <[email protected]> wrote:
> > > >
> > > > > How can I set the ZFS pool ashift for root pools
> > > > > to a value like 14 (for FreeBSD inside a VM)?
> > > > >
> > > > > Lionel
> > > >
> > > >
> > > >
> > > > This has to be done before ZFS pool creation and it can be set like that:
> > > >
> > > > # sysctl vfs.zfs.min_auto_ashift=14
> > >
> > > How can I do this at install time for all root pools?
> > >
> > > Lionel
> >
> > I don't know how to do it if you use the vanilla install CD.  Maybe
> > you could boot the install CD, exit to a shell, set the sysctl, and
> > reenter the TUI.
> >
> > But if you have lots of machines to install, you might consider
> > spinning a custom CD, and if you do that then you can easily set the
> > sysctl or set "-o ashift=14" in ZFSBOOT_BOOT_POOL_CREATE_OPTIONS.  See
> > the SCRIPTING section of bsdinstall(8) for details.
>
> Plain ISO image.
>
> During install I get the question for ZFS options, with noatime being
> in the default string (which we remove, because noatime breaks
> software...) ... can I put the option in there?
>
> Lionel

Yes you can.  But if you do that, you should also uncheck "Force 4K
Sectors", because that will set ashift=12.