Add lvm partition:
pvcreate /dev/hdc3
---------------

vgcreate vg0 /dev/hdc3

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use withexisting lvm volumes on hd :
lvcreate --name firewall --size 1G vg0
mkfs.ext3 /dev/xen-vol/firewall 
mount /dev/vg0/firewall /firewall

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*RESIZE* LVM
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lvextend -L12G /dev/vg0/[name]
or
lvextend -L+1G /dev/vg0/[name]

#XFS file systems must be mounted to be resized and the mount-point is specified rather than the device name.

mount /dev/vg0/[name] /mnt
xfs_growfs /mnt
            
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After hotplugging a harddrive if you want to add the logical volumes:

vgscan
vgchange -ay

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After use:

Unmount file system
Mark the volume group inactive

vgchange -an [volumegroup eg vg0]

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#add new drive with lvm partition to lvm:
pvcreate /dev/[part]
vgextend [volgroup] /dev/[part]

#move data from one particular hd to rest of volume:
pvmove -v /dev/[partition_to_move_from]

#remove old drive from lvm group:
vgreduce [volgroup] /dev/[part]
#The drive can now be either physically removed when the machine is next powered down or reallocated to some other users.
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show size of active lvm's

# lvs --units k
  LV            VG   Attr     LSize          Pool Origin Data%  Move Log Copy%  Convert
  data          pve  -wi-ao--   29294592.00k                                           
  root          pve  -wi-ao--    3903488.00k                                           
  vm-100-disk-1 pve  -wi-a---    5242880.00k                                           
  vm-100-disk-2 pve  -wi-a---    4194304.00k                                           
  vm-101-disk-1 pve  -wi-a---    8388608.00k