Splitting a Volume Group

Splitting a Volume Group

 

Author: Jaylin Zhou

 

Create PVs:
# pvcreate /dev/sdb[567]
  Physical volume "/dev/sdb5" successfully created
  Physical volume "/dev/sdb6" successfully created
  Physical volume "/dev/sdb7" successfully created

 

Create VG:
# vgcreate myvg /dev/sdb[567]
  Volume group "myvg" successfully created

 

Create LV:
# # lvcreate -l 50 /dev/myvg -n mylv
  Logical volume "mylv" created

 

Create filesystem on LV:
# mkfs.ext3 /dev/myvg/mylv

 

Mount LV and Write data on LV

 

Determining Free Space:
Use "pvscan" command to determine how much free space is currently available in the VG
# pvscan
  PV /dev/sdb5   VG myvg   lvm2 [100.00 MB / 0    free]
  PV /dev/sdb6   VG myvg   lvm2 [100.00 MB / 0    free]
  PV /dev/sdb7   VG myvg   lvm2 [100.00 MB / 100.00 MB free]
  Total: 3 [300.00 MB] / in use: 3 [300.00 MB] / in no VG: 0 [0   ]

 

Moving the Data:
Move all the used PE in /dev/sdb5 to /dev/sdb7 with the "pvmove" command
The "pvmove" command can take a long time to execute
# pvmove /dev/sdb5 /dev/sdb7
  /dev/sdb5: Moved: 100.0%
After moving the data, all of the space on /dev/sdb5 is free
# pvscan
  PV /dev/sdb5   VG myvg   lvm2 [100.00 MB / 100.00 MB free]
  PV /dev/sdb6   VG myvg   lvm2 [100.00 MB / 0    free]
  PV /dev/sdb7   VG myvg   lvm2 [100.00 MB / 0    free]
  Total: 3 [300.00 MB] / in use: 3 [300.00 MB] / in no VG: 0 [0   ]

 

Splitting the VG:
Before splitting the VG, the LV must be inactive.
If the file system is mounted, it must be unmounted before deactivating the LV.
Deactivate the LV with the "lvchange" command or "pvchange" command
# lvchange -an /dev/myvg/mylv
Split the VG "yourvg" from the VG "myvg" with moving PV "/dev/sdb5" into the new VG "yourvg"
# vgsplit myvg yourvg /dev/sdb5
  New volume group "yourvg" successfully split from "myvg"
Use the "vgs" command to see the attributes of the two VGs
# vgs
  VG     #PV #LV #SN Attr   VSize   VFree 
  myvg     2   1   0 wz--n- 200.00M      0
  yourvg   1   0   0 wz--n- 100.00M 100.00M

 

Creating the New LV:
Create the new LV "yourlv"
# lvcreate -l 100%FREE /dev/yourvg -n yourlv
  Logical volume "yourlv" created

Making a File System and Mounting the New LV:
# mkfs.ext3 /dev/yourvg/yourlv
# mount /dev/yourvg/yourlv  /mnt/

 

Activating and Mounting the Original LV:
Check the state of the original LV
# lvscan
  inactive          '/dev/myvg/mylv' [200.00 MB] inherit
  ACTIVE            '/dev/yourvg/yourlv' [100.00 MB] inherit
Activate the original LV
# lvchange -ay /dev/myvg/mylv
Check the new state of the original LV
# lvscan
  ACTIVE            '/dev/myvg/mylv' [200.00 MB] inherit
  ACTIVE            '/dev/yourvg/yourlv' [100.00 MB] inherit
# mount /dev/myvg/mylv /mnt/