How to migrate from LVM Partitions to New Logical Volume

To Check Present Logical and Physical Volume

Now we are going to create physical volume, volume group and logical volume for migration. Before moving to the creation of volumes, check the present logical volume data under /mnt/lvm mount point. Now use the following commands to list the mounts

[root@linuxhelp ~]# df -h
Filesystem           Size  Used Avail Use% Mounted on
/dev/sda3             15G  3.8G   11G  26% /
devtmpfs             486M     0  486M   0% /dev
tmpfs                494M  140K  494M   1% /dev/shm
tmpfs                494M  7.1M  487M   2% /run
tmpfs                494M     0  494M   0% /sys/fs/cgroup
/dev/sda1            297M  106M  192M  36% /boot
/dev/sr0             3.9G  3.9G     0 100% /run/media/root/CentOS 7 x86_64
/dev/mapper/vg1-lv1  7.8G   36M  7.3G   1% /mnt/logical
[root@linuxhelp ~]# cd /mnt/logical/
[root@linuxhelp logical]# cat file1.txt 
hello

Welcome To Linux Help !!!!!

Confirm the names of logical volume and volume group and also confirm which physical volume is used to hold them.

[root@linuxhelp logical]# lvs
  LV   VG   Attr       LSize Pool Origin Data%  Move Log Cpy%Sync Convert
  lv1  vg1  -wi-ao---- 8.00g   

To Create New Physical Volume

First define the partition using fdisk and do not forget to change the Type to LVM(8e), while you are creating partitions.

[root@linuxhelp ~]# pvcreate /dev/sdb1 -v
    Set up physical volume for " /dev/sdb1"  with 20971520 available sectors
    Zeroing start of device /dev/sdb1
    Writing physical volume data to disk " /dev/sdb1" 
  Physical volume " /dev/sdb1"  successfully created

Now add the newly created physical volume to existing volume group vg1 using vgextend command

[root@linuxhelp ~]# vgextend vg1 /dev/sdb1
  Volume group " vg1"  successfully extended

To display the full list of information concerning volume group use vgdisplay command.

[root@linuxhelp ~]# vgdisplay vg1 -v
    Using volume group(s) on command line
    Finding volume group " vg1" 
  --- Volume group ---
  VG Name               vg1
  System ID             
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               1
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               19.99 GiB
  PE Size               4.00 MiB
  Total PE              5118
  Alloc PE / Size       2048 / 8.00 GiB
  Free  PE / Size       3070 / 11.99 GiB
  VG UUID               aSuYgU-T4dv-tH5C-dKe6-lgNJ-WWa1-NPgF1k
   
  --- Logical volume ---
  LV Path                /dev/vg1/lv1
  LV Name                lv1
  VG Name                vg1
  LV UUID                IPBCS6-Iokv-9eJR-5z9X-4umT-fGJ7-r5kXXF
  LV Write Access        read/write
  LV Creation host, time linuxhelp, 2016-04-25 14:46:51 +0530
  LV Status              available
  # open                 1
  LV Size                8.00 GiB
  Current LE             2048
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0
   
  --- Physical volumes ---
  PV Name               /dev/sda5     
  PV UUID               2UUFfq-5bOB-Mf7q-oLTB-X5Hf-STQ3-b4dv7Z
  PV Status             allocatable
  Total PE / Free PE    2559 / 511
   
  PV Name               /dev/sdb1     
  PV UUID               qpBHZz-lfVA-LgrE-E4gZ-DWmg-8RJe-NHc0x7
  PV Status             allocatable
  Total PE / Free PE    2559 / 2559

Important: In the above screen, we can see PV has been added to the volume group.

To know more information about which devices are mapped, use the dmsetup dependency command

[root@linuxhelp ~]# dmsetup deps /dev/vg1/lv1
1 dependencies : (8, 5)

LVM Mirroring Procedure

In order to migrate from old logical volume to new drive using Mirroring method, use lvconvert command to migrate data

[root@linuxhelp ~]# lvconvert -m 1 /dev/vg1/lv1 /dev/sdb1
-m = mirror
1 = adding a single mirror

The migration process will take time according to your volume size.

After migration process completed, check the converted mirror.

[root@linuxhelp ~]# lvs -o+devices
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert Devices
lv1 vg1 rwi-aor--- 8.00g 100.00 lv1_rimage_0(0),lv1_rimage_1(0)

After you review the converted mirror, remove the old virtual disk vdb1. The option -m is used to remove the mirror.

[root@linuxhelp ~]# lvconvert -m 0 /dev/vg1/lv1 /dev/sdb1
Logical volume lv1 converted

[root@linuxhelp ~]# lvs -o+devices
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert Devices
lv1 vg1 -wi-ao---- 8.00g /dev/sdb1(1)
[root@linuxhelp ~]# dmsetup deps /dev/vg1/lv1
1 dependencies : (8, 17) 

[root@linuxhelp ~]# cd /mnt/logical/
[root@linuxhelp logical]# ls
file1.txt lost+found
[root@linuxhelp logical]# cat file1.txt
hello

Welcome To Linux Help !!!!!

[root@linuxhelp logical]# vgreduce /dev/vg1 /dev/sda5
Removed " /dev/sda5"  from volume group " vg1" 
[root@linuxhelp logical]# vgs -o+devices
VG #PV #LV #SN Attr VSize VFree Devices
vg1 1 1 0 wz--n- 10.00g 2.00g /dev/sdb1(1)

[root@linuxhelp logical]# lvs
LV VG Attr LSize Pool Origin Data% Move Log Cpy%Sync Convert
lv1 vg1 -wi-ao---- 8.00g

[root@linuxhelp logical]# pvmove -n /dev/vg1/lv1 /dev/sdb1 /dev/sda5