[CentOS] Manual partitioning and LVM

I can't seem to figure out how to partition for install. I've tried both 
CentOS 8 and 7.7 netinstalls.

I've got 3 disks: sda (big hardware RAID array), sdb (SSD), and sdc 
(internal SD card for booting). I want to put /boot on sdc, /usr on sdb, 
and / on sda. I don't care what format is used on sdb and sdc, whatever 
will let it boot. I want LVM on sda so that I can use snapshotting for 
backups.

I can pre-format sdb1 and sdc1 as ext4 usinga gparted live DVD. If I select 
manual partitioning, I can then label and assign those two to /usr and 
/boot. I can see sda in the drives available on the first detination screen 
but but I don't see it in the manual partitioning screen. So I don't see 
how to partition and format it as an LVM volume that I can mount to /.