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

On Tue, 12 May 2026 at 18:03, Alan Somers <[email protected]> wrote:
>
> 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.

Is there a way to autodetect VMware, and then use an ashift balue
which is double the block size of the parent root device? Because
setting the ashift to the block size of a VM disk, which uses the
block size of the parent FS, is a pretty bad idea.

Lionel