vm_snapshot_chain_size in VMware

[knishimoto-idcf]

Let me confirm how to calculate vm_snapshot_chain_size in VMware.

The "volumes" table of CloudStack DB has the column "vm_snapshot_chain_size". We checked #2104 and #5735 to understand the specification of vm_snapshot_chain_size in VMware.

CloudStack seems to consider size of -flat.vmdk, -xxxxxx.vmdk and -xxxxxx-delta.vmdk files when it calculates vm_snapshot_chain_size.

cloudstack/plugins/hypervisors/vmware/src/main/java/com/cloud/hypervisor/vmware/manager/VmwareStorageManagerImpl.java

Lines 1313 to 1322 in 81e052c

	// get volume's chain size for this VM snapshot; exclude current volume vdisk
	ManagedObjectReference morDs = getDatastoreAsManagedObjectReference(baseName, hyperHost, datastoreUuid);
	long size = getVMSnapshotChainSize(context, hyperHost, baseName + "-*.vmdk", morDs, path, vmName);
	if (volumeTO.getVolumeType() == Volume.Type.ROOT) {
	// add memory snapshot size
	size += getVMSnapshotChainSize(context, hyperHost, vmName + "-*.vmsn", morDs, null, vmName);
	}
	volumeTO.setSize(size);

Consider the following cases.

1. No VM snapshot

Create a virtual machine (i-2-268-DEVM).

.vmdk and -flat.vmdk files are created as follows:

[root@esxi67-host01:/vmfs/volumes/a9d31e3b-dd41814d/i-2-268-DEVM] ls -al *vmdk *vmsn
-rw------- 1 root root 16106127360 Sep 17 10:02 i-2-268-DEVM_268-flat.vmdk
-rw------- 1 root root 537 Sep 3 03:36 i-2-268-DEVM_268.vmdk

Is the vm_snapshot_chain_size expected to be 0?

2. One VM snapshot

Create a VM snapshot.

.vmdk and -flat.vmdk files are created as follows:

[root@esxi67-host01:/vmfs/volumes/a9d31e3b-dd41814d/i-2-268-DEVM] ls -al *vmdk *vmsn
-rw------- 1 root root 21577 Sep 17 10:02 i-2-268-DEVM-Snapshot2.vmsn
-rw------- 1 root root 16809984 Sep 17 10:16 i-2-268-DEVM_268-000001-delta.vmdk
-rw------- 1 root root 313 Sep 17 10:06 i-2-268-DEVM_268-000001.vmdk
-rw------- 1 root root 16106127360 Sep 17 10:02 i-2-268-DEVM_268-flat.vmdk
-rw------- 1 root root 537 Sep 3 03:36 i-2-268-DEVM_268.vmdk

Size of current volume vdisk (i-2-268-DEVM_268-000001-delta.vmdk) may grow up to the allocated size (=the value of the "size" column of the "volumes" table). So the total size of the volume may grow up to "the size of i-2-268-DEVM_268-flat.vmdk + the allocated size + the size of i-2-268-DEVM-Snapshot2.vmsn".

Is the vm_snapshot_chain_size expected to be 16106148937 (=16106127360+21577)?

3. Two VM snapshotVM

.vmdk and -flat.vmdk files are created as follows:

[root@esxi67-host01:/vmfs/volumes/a9d31e3b-dd41814d/i-2-268-DEVM] ls -al *vmdk *vmsn
-rw------- 1 root root 21577 Sep 17 10:02 i-2-268-DEVM-Snapshot2.vmsn
-rw------- 1 root root 21581 Sep 17 10:16 i-2-268-DEVM-Snapshot3.vmsn
-rw------- 1 root root 16809984 Sep 17 10:16 i-2-268-DEVM_268-000001-delta.vmdk
-rw------- 1 root root 313 Sep 17 10:06 i-2-268-DEVM_268-000001.vmdk
-rw------- 1 root root 16809984 Sep 17 10:33 i-2-268-DEVM_268-000002-delta.vmdk
-rw------- 1 root root 320 Sep 17 10:16 i-2-268-DEVM_268-000002.vmdk
-rw------- 1 root root 16106127360 Sep 17 10:02 i-2-268-DEVM_268-flat.vmdk
-rw------- 1 root root 537 Sep 3 03:36 i-2-268-DEVM_268.vmdk

Size of current volume vdisk (i-2-268-DEVM_268-000002-delta.vmdk) may grow up to the allocated size (=the value of the "size" column of the "volumes" table). So the total size of the volume may grow up to "the size of i-2-268-DEVM_268-flat.vmdk + i-2-268-DEVM_268-000001.vmdk + i-2-268-DEVM_268-000001-delta.vmdk + the allocated size + the size of i-2-268-DEVM-Snapshot2.vmsn + i-2-268-DEVM-Snapshot3.vmsn".

Is the vm_snapshot_chain_size expected to be 16122980815 (=16106127360+21577+313+16809984+21581)?

[DaanHoogland]

it seems the answer to your question is "almost" as you are skiping the 313 and 320 values for the i-2-268-DEVM_268-000001.vmdk and i-2-268-DEVM_268-000002.vmdk.
Also, Are you asking because you are finding discrepancies.

[knishimoto-idcf]

Thank you so much for your prompt response. I understand.

Also, Are you asking because you are finding discrepancies.

No. But I couldn't see that CloudStack intends to add size of -flat.vmdk file to vm_snapshot_chain_size. -flat.vmdk file is a data disk but not a VM snapshot. The pattern baseName + "-*.vmdk" looks like a pattern to find delta files (-xxxxxx.vmdk, -xxxxxx-delta.vmdk). I couldn't find any documentation about vm_snapshot_chain_size. So, I wanted to clarify the specification.