How to take LMV Snapshots / Backuping LVM via snapshot

A snapshot volume is a special type of volume that presents all the data that was in the volume at the time the snapshot was created.

This means we can back up that volume without having to worry about data being changed while the backup is going on,and we don't have to take the database volume offline while the backup is taking place.

snapshot is just a link which point to another place, if the file is growing in lvm and we need a backup of data at a particular time say @ 6:00 pm, First make a snapshot at 6:00 and and mount it some where and take backup of data from that place. This allows the administrator to create a new block device which presents an exact copy of a logical volume, frozen at some point in time. 

Typically this would be used when some batch processing, a backup for instance, needs to be performed on the logical volume, but you don't want to halt a live system that is changing the data.

When the snapshot device has been finished with the system administrator can just remove the device.

This facility does require that the snapshot be made at a time when the data on the logical volume is in a consistent state.

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              25G  4.9G   19G  21% /
tmpfs                 593M     0  593M   0% /dev/shm
/dev/mapper/vg--ctechz-lvm--ctechz
                      591M  542M   20M  97% /lvm-ctechz

While we are creating a lvm snapshot we are taking space from volume group, so first make sure volume group contain enough free space.

# vgs or vgdisplay

Make sure the snapshot has enough free space or same as origin size(or you can create it in any size)

1.Check in Volume group for free space
# vgs

# vgs
VG        #PV #LV #SN Attr   VSize VFree
vg-ctechz   2   2   1 wz--n- 1.04G 464.00M

free space is available so create a snapshot of current lvm using the vg

# lvcreate -L +400M -s /dev/vg-ctechz/lvm-ctechz -n lvm-ctechz-spapshot1
Logical volume "lvm-ctechz-spapshot1" created

here in plaec of +400M we can give any size, we can even mention +10M as well
-L|--size LogicalVolumeSize
-s|--snapshot} OriginalLogicalVolume[Path]
-n|--name LogicalVolumeName

lvcreate -L +size -s snapshotName -n lvmName

# ls /dev/vg-ctechz/
lvm-ctechz  lvm-ctechz-spapshot1

# mkdir /snapshot
# mount /dev/vg-ctechz/lvm-ctechz-spapshot1 /snapshot/

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              25G  4.9G   19G  21% /
tmpfs                 593M     0  593M   0% /dev/shm
/dev/mapper/vg--ctechz-lvm--ctechz
                      591M  542M   20M  97% /lvm-ctechz
/dev/mapper/vg--ctechz-lvm--ctechz--spapshot1
                      591M  542M   20M  97% /snapshot
 # lvdisplay
  --- Logical volume ---
  LV Name                /dev/vg-ctechz/lvm-ctechz
  VG Name                vg-ctechz
  LV UUID           jZEuoN-16MG-30eX-SZaI-8ETO-ZguH-YRVyeN
  LV Write Access        read/write
  LV snapshot status    source of
              /dev/vg-ctechz/lvm-ctechz-spapshot1[active]
  LV Status              available
   # open                 1
  LV Size                600.00 MB
  Current LE             150
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

  --- Logical volume ---
  LV Name                /dev/vg-ctechz/lvm-ctechz-spapshot1
  VG Name                vg-ctechz
  LV UUID                kk3Cvm-Il4z-J8Kt-qt8s-TstZ-Peyw-gU0Uho
  LV Write Access        read/write
  LV snapshot status     active destination for 
                         /dev/vg-ctech/lvm-ctechz
  LV Status              available
  # open                 1
  LV Size                600.00 MB
  Current LE             150
  COW-table size         400.00 MB
  COW-table LE           100
  Allocated to snapshot  0.01%
  Snapshot chunk size    4.00 KB
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1


# lvdisplay /dev/vg-ctechz/lvm-ctechz
--- Logical volume ---
  LV Name                /dev/vg-ctechz/lvm-ctechz
  VG Name                vg-ctechz
  LV UUID                jZEuoN-16MG-30eX-SZaI-8ETO-ZguH-YRVyeN
  LV Write Access        read/write
LV snapshot status     source of 
               /dev/vg-ctechz/lvm-ctechz-spapshot1[active]
  LV Status              available
  # open                 1
  LV Size                600.00 MB
  Current LE             150
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

Here we can get the status of the active snapshot

Now we created the Snapshot for the Logical Volume what we have and then do the backup, so first create the snapshot and then backup. 

For backuping use your methods or strategy 

# tar -cvf lvmsnap1.tar /dev/mapper/vg--ctechz-lvm--ctechz--spapshot1