Nested logical volume snapshot on shared storage

Nested logical volume snapshot on shared storage

[Mitsuhiro Tanino]

Hi

I would like to know latest activity of nested logical volume snapshot.
In my understanding, nested LV snapshot is only supported when we use LVM thin volume.
Referring the document, thin volume are not supported across the nodes in a cluster
or shared with several servers. Therefore, there is no feature to provide nested
LV snapshot across several nodes.

https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/thinprovisioned_volumes.html

I think nested logical volume snapshot is very useful feature for cloud environment.
For example,
If user create a new VM from LV snapshot, the VM can boot quickly because LVM snapshot
is ablle to create rapidly and also it can save disk usage.
And if nested LV snapshot is supported, user can retrieve a VM which is created by
LV snapshot to former state after applying some configurations. Nested snapshot
is already supported by qcow2.

Following figure is shown above example.
I would appreciate if anyone let me know an activity of nested snapshot.

---------
* Mgmt node(serv01): Manage. volume creation using snapshot, volume deletion
                      snapshot creation using nested LVM snapshot, snapshot deletion
* HV node1(srv02)  : Attach a snapshot to a VM and run KVM guest.
* HV node2(srv03)  : Same as HV node1.
  
  thX: thin volume including KVM guest boot image.
  snX: snapshot from thin volume.

+---------------+  +---------------+  +---------------+
|     srv01     |  |     srv02     |  |     srv03     |
|   Mgmt node   |  |    HV node1   |  |    HV node2   |
|               |  |       +---+   |  |         +---+ |
|               |  |       |VM1|   |  |         |VM2| |
|               |  |       +-+-+   |  |         +-+-+ |
|               |  |         |     |  |             | |
+---+---+---+---+  +---+---+-+-+---+  +---+---+---+-+-+
|th1|th2|sn1|sn2|  |th1|th2|sn1|sn2|  |th1|th2|sn1|sn2|
+---------------+  +---------------+  +---------------+
|   dm-thin01   |  |   dm-thin01   |  |   dm-thin01   |
+---------------+  +---------------+  +---------------+
|     vg01      |  |     vg01      |  |     vg01      |
+---------------+  +---------------+  +---------------+
       |FC1               |FC2               |FC3
       |                  |                  |
------+------------------+--------+---------+----------
                                   |
                           +-------+--------+
                           | A Logical Unit |
                           +----------------+

-- 
Regards,
Mitsuhiro Tanino