after you create the pv
you do this: vgdisplay testvg | grep "Total PE"
lvcreate -l 10230 testvg -n "whatevername"
not 10230
-l is the number you got from the grep
then it will be in /dev
vgcreate backup_sdb /dev/sdb
vgdisplay backup_sdb | grep "Total PE"
lvcreate -l 131274 backup_sdb -n "lv_sdb"
pvdisplay /dev/sdb
lvcreate -L500000 -nVdomains backup_sdb
pvdisplay /dev/sdb
mount /dev/backup_sdb/Vdomains /mnt/test
mke2fs -j /dev/backup_sdb/Vdomains
lvcreate -L100000 -nserver3701 backup_sdb
mke2fs -j /dev/backup_sdb/server3701
mount
dmesg