This page needs cleaning, ref https://help.ubuntu.com/community/Installation/RAID1%2BLVM
Before creating the RAID volume, be sure to partition the entirety of all disks to be used with type “Linux raid auto” (code 0xfd).
mdadm --create /dev/md0 --verbose --level=5 --raid-devices=6 /dev/sdg1 /dev/sdh1 /dev/sdi1 /dev/sdj1 /dev/sdk1 /dev/sdl1 mdadm --manage --add /dev/md0 /dev/sdd1
pvcreate /dev/md0 vgcreate datavg /dev/md0 lvcreate --name datalv --size 179.99G datavg lvextend -L +1G -t /dev/datavg/datalv mkfs.ext3 -m 0 -t largefile /dev/datavg/datalv
apt-get install mdadm lvm2
After install those tools, you can assemble the existing raid and finally scan for the lvm:
mdadm --assemble /dev/md0 /dev/sda1 /dev/sdb1 mdadm --detail --scan vgchange -a y
fstab entry
/dev/datavg/datalv /mnt/data ext4 errors=remount-ro 0 1