vdo create --name=vdo_data --device=/dev/mapper/luks-422d7f7c-2d98-48df-abe5-239def725f18 --vdoLogicalSize=18G (if the drive is over 16TB add this switch also: --vdoSlabSize=8G)
check for cache type: cat /sys/block/sdb/device/scsi_disk/0\:0\:1\:0/cache_type - if none or write through do the following:
vdo changeWritePolicy --writePolicy=sync --name=vdo_data
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If not using LVM you can make the filesystem now.
mkfs.xfs -K /dev/mapper/vdo_data
mkdir /mnt/vdo_data
nano /etc/fstab
/dev/mapper/vdo_data /mnt/vdo_data xfs defaults,x-systemd.requires=vdo.service 0 0
mount -a
df -h
vdostat --human-readable