8.7. Tracking and displaying removed thin snapshot volumes

Procédure

1. Ensure that historical logical volumes are retained by setting record_lvs_history=1 in the lvm.conf file. This metadata option is not enabled by default.
2. Optional: Set the value of the lvs_history_retention_time option in seconds. This is the time interval after which a record about individual historical logical volume is automatically destroyed. The automatic default value is 0 and it disables this feature. If you do not set this option, you can also delete individual historical volumes manually.

3. To display a thin-provisioned snapshot chain:

   Dans cet exemple :

   • lvol1 is an origin volume, the first volume in the chain.
   • lvol2 is a snapshot of lvol1.
   • lvol3 is a snapshot of lvol2.
   • lvol4 is a snapshot of lvol3.

   • lvol5 is also a snapshot of lvol3.

     # lvs -H -o name,full_ancestors,full_descendants
       LV    FAncestors        FDescendants
       lvol1                   lvol2,lvol3,lvol4,lvol5
       lvol2 lvol1             lvol3,lvol4,lvol5
       lvol3 lvol2,lvol1       lvol4,lvol5
       lvol4 lvol3,lvol2,lvol1
       lvol5 lvol3,lvol2,lvol1
       pool

     Note that, despite using lvs utility with the -H option, no thin snapshot volume is removed and there are no historical logical volumes to display.

4. Remove logical volume lvol3 from the snapshot chain:

   # lvremove -f vg/lvol3
     Logical volume "lvol3" successfully removed

5. Run the lvs utility to see the details of historical logical volumes, along with their ancestors and descendants:

   # lvs -H -o name,full_ancestors,full_descendants
     LV     FAncestors         FDescendants
     lvol1                     lvol2,-lvol3,lvol4,lvol5
     lvol2  lvol1              -lvol3,lvol4,lvol5
     -lvol3 lvol2,lvol1        lvol4,lvol5
     lvol4  -lvol3,lvol2,lvol1
     lvol5  -lvol3,lvol2,lvol1
     pool

6. Additionally, display the removal timestamp of a historical volume:

   # lvs -H -o name,full_ancestors,full_descendants,time_removed
     LV     FAncestors         FDescendants              RTime
     lvol1                     lvol2,-lvol3,lvol4,lvol5
     lvol2  lvol1              -lvol3,lvol4,lvol5
     -lvol3 lvol2,lvol1        lvol4,lvol5               2016-03-14 14:14:32 +0100
     lvol4  -lvol3,lvol2,lvol1
     lvol5  -lvol3,lvol2,lvol1
     pool

7. You can reference historical logical volumes individually in a display command by specifying the vgname/lvname format:

   # lvs -H vg/-lvol3
     LV     VG   Attr       LSize
     -lvol3 vg   ----h-----    0

   Note that the fifth bit in the lv_attr field is set to h to indicate the volume is a historical one.

8. LVM does not keep historical logical volumes if the volume has no live descendant. This means that if you remove a logical volume at the end of a snapshot chain, the logical volume is not retained as a historical logical volume.

   # lvremove -f vg/lvol5
     Automatically removing historical logical volume vg/-lvol5.
     Logical volume "lvol5" successfully removed
   # lvs -H -o name,full_ancestors,full_descendants
     LV     FAncestors         FDescendants
     lvol1                     lvol2,-lvol3,lvol4
     lvol2  lvol1              -lvol3,lvol4
     -lvol3 lvol2,lvol1        lvol4
     lvol4  -lvol3,lvol2,lvol1
     pool

9. Remove the volume lvol1 and lvol2 and to see how the lvs command displays the volumes once they have been removed.

   # lvremove -f vg/lvol1 vg/lvol2
     Logical volume "lvol1" successfully removed
     Logical volume "lvol2" successfully removed
   # lvs -H -o name,full_ancestors,full_descendants
     LV     FAncestors           FDescendants
     -lvol1                      -lvol2,-lvol3,lvol4
     -lvol2 -lvol1               -lvol3,lvol4
     -lvol3 -lvol2,-lvol1        lvol4
     lvol4  -lvol3,-lvol2,-lvol1
     pool

10. Remove a historical logical volume completely by specifying the name of the historical volume that now includes the hyphen, as in the following example

    # lvremove -f vg/-lvol3
    Historical logical volume "lvol3" successfully removed
    # lvs -H -o name,full_ancestors,full_descendants
      LV     FAncestors    FDescendants
      -lvol1               -lvol2,lvol4
      -lvol2 -lvol1        lvol4
      lvol4  -lvol2,-lvol1
      pool