Creating 4k-aligned FreeBSD slices with headroom

gistfile1.sh

gpart create -s GPT ada1 
gpart create -s GPT ada2 
gpart create -s GPT ada3 

# find out the sector count of each of these disks 
dmesg | grep ada | grep sectors 

# OK, 3,907,029,168 512-byte sectors per disk. 
# make a bunch of disks that use up a little bit less space than max 
# in case I need to replace one of these drives with slightly fewer sectors 

gpart add -b 2048 -s 3906824301 -t freebsd-zfs -l power ada1 
gpart add -b 2048 -s 3906824301 -t freebsd-zfs -l wisdom ada2 
gpart add -b 2048 -s 3906824301 -t freebsd-zfs -l courage ada3 

gnop create -S 4096 gpt/power 
gnop create -S 4096 gpt/wisdom 
gnop create -S 4096 gpt/courage 

zpool create triforce raidz gpt/power.nop gpt/wisdom.nop gpt/courage.nop 
zdb | grep ashift # verify ashift is 12 for a 4K-aligned disk 

# kick out the 4k-alignment struts 
zpool export triforce 
gnop destroy gpt/power.nop gpt/wisdom.nop gpt/courage.nop 
# -d: look in /dev/gpt (to keep labels) 
zpool import -d /dev/gpt triforce