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