8.5. Creating thinly-provisioned snapshot volumes

Conditions préalables

• You have created a thinly-provisioned logical volume. For more information, see Overview of thin provisioning.

Procédure

• Create a thinly-provisioned snapshot volume. The following command creates a thinly-provisioned snapshot volume named as mysnapshot1 of the thinly-provisioned logical volume vg001/thinvolume:

  # lvcreate -s --name mysnapshot1 vg001/thinvolume
    Logical volume "mysnapshot1" created

  # lvs
    LV          VG       Attr     LSize   Pool       Origin     Data%  Move Log Copy%  Convert
    mysnapshot1 vg001    Vwi-a-tz   1.00g mythinpool thinvolume   0.00
    mythinpool  vg001    twi-a-tz 100.00m                         0.00
    thinvolume  vg001    Vwi-a-tz   1.00g mythinpool              0.00

  Note

  When using thin provisioning, it is important that the storage administrator monitor the storage pool and add more capacity if it starts to become full. For information on extending the size of a thin volume, see Creating thinly-provisioned logical volumes .

• You can also create a thinly-provisioned snapshot of a non-thinly-provisioned logical volume. Since the non-thinly-provisioned logical volume is not contained within a thin pool, it is referred to as an external origin. External origin volumes can be used and shared by many thinly-provisioned snapshot volumes, even from different thin pools. The external origin must be inactive and read-only at the time the thinly-provisioned snapshot is created.

  The following example creates a thin snapshot volume of the read-only, inactive logical volume named origin_volume. The thin snapshot volume is named mythinsnap. The logical volume origin_volume then becomes the thin external origin for the thin snapshot volume mythinsnap in volume group vg001 that uses the existing thin pool vg001/pool. The origin volume must be in the same volume group as the snapshot volume. Do not specify the volume group when specifying the origin logical volume.

  # lvcreate -s --thinpool vg001/pool origin_volume --name mythinsnap

• You can create a second thinly-provisioned snapshot volume of the first snapshot volume by executing the following command.

  # lvcreate -s vg001/mysnapshot1 --name mysnapshot2
  Logical volume "mysnapshot2" created.

  To create a third thinly-provisioned snapshot volume, use the following command:

  # lvcreate -s vg001/mysnapshot2 --name mysnapshot3
  Logical volume "mysnapshot3" created.

Vérification

• Display a list of all ancestors and descendants of a thin snapshot logical volume:

  $ lvs -o name,lv_ancestors,lv_descendants vg001
    LV           Ancestors                           Descendants
    mysnapshot2  mysnapshot1,thinvolume              mysnapshot3
    mysnapshot1  thinvolume              mysnapshot2,mysnapshot3
    mysnapshot3  mysnapshot2,mysnapshot1,thinvolume
    mythinpool
    thinvolume           	           	     mysnapshot1,mysnapshot2,mysnapshot3

  Here,

• thinvolume is an origin volume in volume group vg001.
• mysnapshot1 is a snapshot of thinvolume
• mysnapshot2 is a snapshot of mysnapshot1

• mysnapshot3 is a snapshot of mysnapshot2

  Note

  The lv_ancestors and lv_descendants fields display existing dependencies. However, they do not track removed entries which can break a dependency chain if the entry was removed from the middle of the chain.