From: "Theo de Raadt" <deraadt@openbsd.org>
Subject: Re: New 'Select root disk by size' install option
To: Eric Radman <ericshane@eradman.com>
Cc: tech@openbsd.org
Date: Mon, 02 Mar 2026 09:50:03 -0700

Your solution doesn't make any sense to me because your thesis is
"I don't have information to make a decision", and then ... you don't add
new information.

Eric Radman <ericshane@eradman.com> wrote:

> For systems with more than one disk, the order of sd(4) devices make it
> very likely that autoinstall will destroy a volume intended only for
> data.  In the following example, sd1 (at sdmmc0) is the intended target,
> but if an NVMe or a second SATA devices is added, the correct choice
> will become sd2:
> 
>     sd0: ATA, ST5000LM000-2U81, 0001 naa.5000c500eb875982 (4657.5G)
>     sd1: Samsung, BJTD4R, 0000  (29.1G)
> 
> To guard against this, you really have to reboot, double-check the
> device assignments, then reboot again to begin the install.
> 
> The attached patch allows autoinstall to sort disks based on expected
> size.  Devices between 1 and 1000GB are presented as the default choice:
> 
> Select root disk by size? (range in GB) [1-1000]
> Available disks are: sd0 sd1 sd2 sd3.
> Which disk is the root disk? ('?' for details) [sd2] ?
>     sd0: VirtIO, Block Device  (0.5G)
>     sd1: VirtIO, Block Device  (4096.0G)
>     sd2: VirtIO, Block Device  (5.0G)
>     sd3: VirtIO, Block Device  (10.0G)
> 
> As before, any disk may be selected, but this provides a mechanism for
> picking a plausible install target.
> 
>  M  distrib/miniroot/install.sub  |  14+  2-
> 
> 1 file changed, 14 insertions(+), 2 deletions(-)
> 
> commit - 3ef2b96be9966a1f84c2f3fa4bd67478f0f4f427
> commit + c2aab348274a0ce641ccc0be6571e9cfebdee06a
> blob - dea8764f006a2cdfc4fb07984009b313d0e6e4a6
> blob + 8ca3676c4c316c09714179de0f749ae96dbbeb94
> --- distrib/miniroot/install.sub
> +++ distrib/miniroot/install.sub
> @@ -2432,15 +2432,27 @@ is_rootdisk() {
>  # Get global root information. ie. ROOTDISK, ROOTDEV and SWAPDEV.
>  get_rootinfo() {
>  	local _rootdisks=$(get_dkdevs_root) _dkdev
> +	local _size_gb _size_min=1 _size_max=1000
>  	local _q="Which disk is the root disk? ('?' for details)"
>  
> -	
>  	if [[ $MODE == install ]]; then
>  		# Prefer disks bigger than 1G as small ones tend to be install
>  		# media, softraid(4) key disks or tiny USB sticks or SD cards.
> +		# Also avoid large storage devices if other disks are available.
> +		while :; do
> +			ask_until "Select root disk by size? (range in GB)" "$_size_min-$_size_max"
> +			_size_min=${resp%%-*}
> +			_size_max=${resp##*-}
> +			[[ $_size_max -gt $_size_min ]] && break
> +			echo "Invalid range"
> +		done
> +
>  		for _dkdev in $_rootdisks; do
> -			diskinfo $_dkdev | grep -q '(0\..*G)$' &&
> +			_size_gb=$(diskinfo $_dkdev | sed -E 's/.*\(([0-9]+).*\)$/\1/')
> +			[[ $_size_gb -ge $_size_min ]] ||
>  				_rootdisks="$(rmel "$_dkdev" $_rootdisks) $_dkdev"
> +			[[ $_size_gb -lt $_size_max ]] ||
> +				_rootdisks="$(rmel "$_dkdev" $_rootdisks) $_dkdev"
>  		done
>  	fi
>  
>