$ sudo pvcreate /dev/nvme0n1
  Physical volume "/dev/nvme0n1" successfully created.
$ sudo pvcreate /dev/sdb
  Physical volume "/dev/sdb" successfully created.
  
$ sudo vgcreate vg-cache /dev/nvme0n1 /dev/sdb
  Volume group "vg-cache" successfully created

$ sudo lvcreate -n slow -l90%FREE vg-cache /dev/sdb
  Logical volume "slow" created.

$ sudo lvcreate -n fast -L 10G vg-cache /dev/nvme0n1

$ sudo modprobe dm-writecache

$ sudo lvchange -a n vg-cache/fast

$ sudo lvchange -a n vg-cache/slow

$ sudo lvconvert --type writecache --cachevol fast vg-cache/slow

$ sudo lvchange -a y vg-cache/slow

$ sudo lvconvert --splitcache vg-cache/slow

$ sudo blockdev --getsz /dev/vg-cache/slow
12744687616

$ sudo dmsetup create wc --table "0 78151680 writecache s /dev/vg-cache/slow /dev/vg-cache/fast 4096 0"

$ sudo dmsetup message /dev/mapper/wc 0 flush

$ dmsetup remove /dev/mapper/wc