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5.3. Splitting a Volume Group

In this example procedure, an existing volume group consists of three physical volumes. If there is enough unused space on the physical volumes, a new volume group can be created without adding new disks.
In the initial set up, the logical volume mylv is carved from the volume group myvol, which in turn consists of the three physical volumes, /dev/sda1, /dev/sdb1, and /dev/sdc1.
After completing this procedure, the volume group myvg will consist of /dev/sda1 and /dev/sdb1. A second volume group, yourvg, will consist of /dev/sdc1.
  1. Use the pvscan command to determine how much free space is currently available in the volume group. 
    # pvscan
  PV /dev/sda1  VG myvg   lvm2 [17.15 GB / 0    free]
  PV /dev/sdb1  VG myvg   lvm2 [17.15 GB / 12.15 GB free]
  PV /dev/sdc1  VG myvg   lvm2 [17.15 GB / 15.80 GB free]
  Total: 3 [51.45 GB] / in use: 3 [51.45 GB] / in no VG: 0 [0   ]
  2. Move all the used physical extents in /dev/sdc1 to /dev/sdb1 with the pvmove command. The pvmove command can take a long time to execute. 
    # pvmove /dev/sdc1 /dev/sdb1
  /dev/sdc1: Moved: 14.7%
  /dev/sdc1: Moved: 30.3%
  /dev/sdc1: Moved: 45.7%
  /dev/sdc1: Moved: 61.0%
  /dev/sdc1: Moved: 76.6%
  /dev/sdc1: Moved: 92.2%
  /dev/sdc1: Moved: 100.0%
    After moving the data, you can see that all of the space on /dev/sdc1 is free. 
    # pvscan
  PV /dev/sda1   VG myvg   lvm2 [17.15 GB / 0    free]
  PV /dev/sdb1   VG myvg   lvm2 [17.15 GB / 10.80 GB free]
  PV /dev/sdc1   VG myvg   lvm2 [17.15 GB / 17.15 GB free]
  Total: 3 [51.45 GB] / in use: 3 [51.45 GB] / in no VG: 0 [0   ]
  3. To create the new volume group yourvg, use the vgsplit command to split the volume group myvg.
    Before you can split the volume group, the logical volume must be inactive. If the file system is mounted, you must unmount the file system before deactivating the logical volume.
    Deactivate the logical volumes with the lvchange command or the vgchange command. The following command deactivates the logical volume mylv and then splits the volume group yourvg from the volume group myvg, moving the physical volume /dev/sdc1 into the new volume group yourvg. 
    # lvchange -a n /dev/myvg/mylv
# vgsplit myvg yourvg /dev/sdc1
  Volume group "yourvg" successfully split from "myvg"
    You can use the vgs command to see the attributes of the two volume groups. 
    # vgs
  VG     #PV #LV #SN Attr   VSize  VFree
  myvg     2   1   0 wz--n- 34.30G 10.80G
  yourvg   1   0   0 wz--n- 17.15G 17.15G
  4. After creating the new volume group, create the new logical volume yourlv. 
    # lvcreate -L 5G -n yourlv yourvg
  Logical volume "yourlv" created
  5. Create a file system on the new logical volume and mount it. 
    #  mkfs.gfs2 -p lock_nolock -j 1 /dev/yourvg/yourlv
This will destroy any data on /dev/yourvg/yourlv.

Are you sure you want to proceed? [y/n] y

Device:                    /dev/yourvg/yourlv
Blocksize:                 4096
Filesystem Size:           1277816
Journals:                  1
Resource Groups:           20
Locking Protocol:          lock_nolock
Lock Table:

Syncing...
All Done

# mount /dev/yourvg/yourlv /mnt
  6. Since you had to deactivate the logical volume mylv, you need to activate it again before you can mount it. 
    # lvchange -a y /dev/myvg/mylv

# mount /dev/myvg/mylv /mnt
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/yourvg/yourlv    24507776        32  24507744   1% /mnt
/dev/myvg/mylv        24507776        32  24507744   1% /mnt
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