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

On 12/05/2026 18:14, Lionel Cons wrote:
> On Tue, 12 May 2026 at 18:03, Alan Somers <[email protected]> wrote:

[..]

>> 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.
You can check `kenv` variables

# kenv | grep system
smbios.system.maker="VMware, Inc."
smbios.system.product="VMware Virtual Platform"
smbios.system.serial="VMware-42 xx xx xx xx xx xx xx"
smbios.system.uuid="42xxxxxxxxxxxxxx"
smbios.system.version="None"

But detection of the block size depends on the device VMware emulates. 
Most of the time it can be seen in `diskinfo -v` output (sectorsize or 
stripesize), but many times it shows 512 even if underlying storage has 
much bigger blocks. Then you need to find other commands for specific 
disk / storage type. For example NVME disks can use `nvmecontrol 
identify`. Don't know much about VMware emulated disks. All I have 
access is SCSI type da0 etc.

Miroslav Lachman