Tuesday, April 09, 2019

What NSX-T Manager appliance size is good for your environment?

NSX-T 2.4 has NSX Manager and NSX Controller still logically separated but physically integrated within a single virtual appliance which can be clustered as a 3-node management/controller cluster. So the first typical question during NSX-T design workshop or before NSX-T implementation is what NSX-T Manager appliance size is good for my environment.

In NSX-T 2.4 documentation (NSX Manager VM System Requirements) are documented following NSX Manager Appliance sizes.

Appliance Size
Disk Space
VM Hardware Version
NSX Manager Extra Small
8 GB
200 GB
10 or later
NSX Manager Small VM
16 GB
200 GB
10 or later
NSX Manager Medium VM
24 GB
200 GB
10 or later
NSX Manager Large VM
48 GB
200 GB
10 or later
In the above documentation section is written that
  • The NSX Manager Extra Small VM resource requirements apply only to the Cloud Service Manager.
  • The NSX Manager Small VM appliance size is suitable for lab and proof-of-concept deployments.
So for NSX-T on-prem production usage, you can use Medium and Large size. But which one? The NSX-T documentation section (NSX Manager VM System Requirements) has no more info to support your design or implementation decision. However, in another part of the documentation (Overview of NSX-T Data Center) is written that
  • The NSX Manager Medium appliance is targeted for deployments up to 64 hosts
  • The NSX Manager Large appliance for larger-scale environments.


Long story short, only Medium and Large sizes are targeted to On-Prem NSX-T production usage. The Medium size should be used in an environment up to 64 ESXi hosts. For larger environments, the Large size is the way to go.

Hope this helps to your NSX-T Plan, Design, and Implement exercise.

Friday, April 05, 2019

vSAN : Number of required ESXi hosts

As you have found this article, I would assume that you know what vSAN is. For those who are new to vSAN, below is the definition from https://searchvmware.techtarget.com/definition/VMware-VSAN-VMware-Virtual-SAN
VMware vSAN (formerly Virtual SAN) is a hyper-converged, software-defined storage (SDS) product developed by VMware that pools together direct-attached storage devices across a VMware vSphere cluster to create a distributed, shared data store. The user defines the storage requirements, such as performance and availability, for virtual machines (VMs) on a VMware vSAN cluster and vSAN ensures that these policies are administered and maintained.
VMware vSAN aggregates local or direct-attached data storage devices to create a single storage pool shared across all ESXi hosts in the vSAN (aka vSphere) cluster. vSAN eliminates the need for external shared storage and simplifies storage configuration and virtual machine provisioning. Data are protected across ESXi hosts. To be more accurate across failure domains, but let's assume we stick with the vSAN default failure domain, which is ESXi host.

vSAN is policy-based storage and policy dictates how data will be redundant, distributed, reserved, etc. You can treat a policy as a set of requirements you can define and storage system will try to deploy and operate the storage object in compliance with these requirements. If it cannot satisfy requirements defined in a policy, the object cannot be deployed or, if already deployed, it becomes in the non-compliant state, therefore at risk.

vSAN is object storage, therefore each object is composed of multiple components.

Let's start with RAID-1. For RAID-1, components can be replicas or witnesses.
Replicas are components containing the data.
Witnesses are components containing just metadata used to avoid split-brain scenario.

Objects components are depicted on the screenshot below where you can see three objects
  1. VM Home 
  2. VM Swap
  3. VM Disk
where each object has two components (data replicas) and one witness (component containing just metadata). 
vSAN Components

The key concept of data redundancy is FTT.  FTT is the number of failures to tolerate. To tolerate failures, vSAN supports two methods of data distribution across vSAN nodes (actually ESXi hosts). It is often referenced as an FTM (Failure Tolerance Method). FTM can be
  • RAID-1 (aka Mirroring)
  • RAID-5/6 (aka Erasure Coding)
As data are distributed across nodes to achieve redundancy and not disks, I'd rather call it RAIN than RAID. Anyway, vSAN terminology uses RAID, so let stick with RAID.

In the table below, you can see how many hosts you need to achieve particular FTT for FTM RAID-1 (Mirroring):

FTTReplicasWitness componentsMinimum # of hosts

In the table below, you can see how many hosts you need to achieve particular FTT for FTM RAID-5/6 (Erasure Coding):
FTTErasure codingRedundancyMinimum # of hosts
0NoneNo redundancy1

Design consideration: 
The above number of ESXi hosts are minimal. What does it mean? In case of longer ESXi host maintenance or long-time server failure, vSAN will not be able to rebuild components from affected ESXi node somewhere else. That's the reason why at least one additional ESXi host is highly recommended. Without one additional ESXi host, there can be situations, your data are not redundant, therefore unprotected. 

I have written this article mainly for myself to use it as a quick reference during conversations with customers. Hope you will find it useful as well.

Friday, March 22, 2019

VMware SSO domain design and operational management

Before we will deep dive into VMware SOO management, it is good to understand its architecture and discuss some design considerations. I highly recommend watching the following video

If you have not watched the video yet, do NOT continue and watch it.

The video is great but it is worth to mention that vSphere 6.7 and 6.7U1 come up with few significant improvements in terms of PSC. You can read more about it in the article "External Platform Services Controller, A Thing of the Past". The overall concept stays the same but following enhancements were released:
  • vSphere 6.7 and vSphere 6.5 Update 2 introduced enhanced linked mode support for embedded PSC deployments.
  • The converge utility in vSphere 6.7 Update 1 allows customers with an external PSC deployment to migrate to an embedded PSC deployment. 
  • In vSphere 6.7 is the repoint tool. A stand-alone embedded deployment can join or leave a vSphere SSO Domain. Domain repoint is a feature available in vSphere 6.7 using the cmsso-util CLI command. You can repoint an external vCenter Server across a vSphere SSO domain. New in vSphere 6.7 Update 1 is support for embedded deployment domain repoint. 
So now you should understand VMware architectural basics and we can deep dive into common management operations which can be used also for design verifications.

What is my SSO Domain Name?

It is good to know what is the SSO Domain Name. If I'm logged in PSC (or VCSA /w embedded PSC), following command will show me what is the SSO domain of this particular domain controller (aka PSC)
/usr/lib/vmware-vmafd/bin/vmafd-cli get-domain-name --server-name localhost

The output in my home lab is following

 root@vc01 [ ~ ]# /usr/lib/vmware-vmafd/bin/vmafd-cli get-domain-name --server-name localhost  

So my SSO domain is uw.cz

Where my Lookup Service is running?

VCSA command
/usr/lib/vmware-vmafd/bin/vmafd-cli get-ls-location --server-name localhost
show the location of lookup service.

The output in my home lab is following

 root@vc01 [ ~ ]# /usr/lib/vmware-vmafd/bin/vmafd-cli get-ls-location --server-name localhost  

So my lookup service is located at  https://vc01.home.uw.cz/lookupservice/sdk  

What is the SSO Site Name?

VCSA command
/usr/lib/vmware-vmafd/bin/vmafd-cli get-site-name --server-name localhost
show the site name where particular domain controller (aka PSC) is located.

The output in my home lab is following

 root@vc01 [ ~ ]# /usr/lib/vmware-vmafd/bin/vmafd-cli get-site-name --server-name localhost  

So my PSC is on site ledcice which is the village name where my home lab is located.

Domain replication agreements

If I have more PSCs in SSO Domain, I can determine replication agreements and status by command vdcrepadmin as shown below.

cd /usr/lib/vmware-vmdir/bin

./vdcrepadmin -f showservers -h PSC_FQDN -u administrator -w Administrator_Password
./vdcrepadmin -f showpartners -h PSC_FQDN -u administrator -w Administrator_Password
./vdcrepadmin -f showpartnerstatus -h localhost -u administrator -w Administrator_Password
./vdcrepadmin -f createagreement -2 -h Source_PSC_FQDN -H New_PSC_FQDN_to_Replicate -u ./administrator -w Administrator_Password
./vdcrepadmin -f removeagreement -2 -h Source_PSC_FQDN \
-H PSC_FQDN_to_Remove_from_Replication -u administrator -w Administrator_Password

These procedures are documented in VMware KB "Determining replication agreements and status with the Platform Services Controller 6.x (2127057)" available at https://kb.vmware.com/kb/2127057

Domain repoint

Domain repoint is a feature available since vSphere 6.5 using the cmsso-util CLI command. You can repoint an external vCenter Server from one PSC to another PSC within the same vSphere SSO domain. Data migration for such repointing is not necessary as all data are replicated across all PSC's within SSO domain. vSphere 6.7 U1 also supports repointing across different SSO domains along with data migrations.

With cmssso-util you can do the following operations
See the cmsso-util CLI command help in the screenshot below

 root@vc01 [ ~ ]# cmsso-util  
 usage: cmsso-util [-h] {unregister,reconfigure,repoint,domain-repoint} ...  
 Tool for orchestrating unregister of a node from LS, reconfiguring a vCenter Server with embedded PSC and repointing a vCenter Server to an external  
 PSC in same as well as different domain.  
 positional arguments:  
   unregister     Unregister node. Passing --node-pnid will unregister solution users, computer account and service endpoints. Passing --hostId  
             will unregister only service endpoints and solution users.  
   reconfigure     Reconfigure a vCenter with an embedded Platform Services Controller(PSC) to a vCenter Server. Then it repoints to the provided  
             external PSC node.  
   repoint       Repoints a vCenter with an external Platform Services Controller(PSC) to the provided external PSC node.  
   domain-repoint   Repoint Embedded vCenter Server from one vCenter Server to another given domain. The repoint operation will migrate Tags,  
             Authorization, License data to another Embedded node.  
 optional arguments:  
  -h, --help      show this help message and exit  

Command to unregister system vc02.home.uw.cz would look like
cmsso-util unregister --node-pnid vc02.home.uw.cz --username administrator --passwd VMware1! 

How to decommission/remove a PSC from SSO domain?

You should use cmsso-util unregister command to unregister the Platform Services Controller, however sometimes you can get the error, therefore there is another way how to unregister failed PSCs from the SSO database. You can use the command
/usr/lib/vmware-vmdir/bin/vdcleavefed -h hostname -u administrator -w PASSWORD
where hostname is the hostname of the PSC that must be removed.

Usage: vdcleavefed [ -h ] -u [-w ]
        implying offline mode if is provided, and the server must have been down.

        implying online mode if is not provided

It actually alters SSO configuration and removes federation.

How to converge VMware SSO domain topology?

Before vSphere 6.7 U1, there was no way how to converge existing SSO topology, however, vSphere 6.7 U1 allows such convergence. If you have deployed or installed a vCenter Server instance with an external Platform Services Controller, you can convert it to a vCenter Server instance with an embedded Platform Services Controller using the converge utility vcsa-util. You can locate the vcsa-util utility in the vcsa-converge-cli directory in vCenter installation media (DVD).

With vcsa-coverge-cli you can do the following operations

For further practical information and examples, you can read following blog posts


I prefer simplicity over complexity, therefore I personally like all improvements vSphere 6.7 U1 brings into the table. I'm always trying to keep SSO topology as simple as possible. However, in large environments with multiple sites across multiple regions, there can be requirements leading to more complex SSO topologies.

Hope this blog post is useful at least for one other person than me. If you know some other commands or ways how to manage VMware SSO domain, please leave the comment below this blog post. 

Thursday, March 14, 2019

How to transfer large ISO files to ESXi Datastore with USB disk?

I'm participating in one VMware virtualization PoC and we had a need to transfer large ISO file to VMFS datastore on standalone ESXi host. Normally you would upload ISO files over the network but PoC network was only 100Mbps so we would like to use USB disk to transfer ISOs to ESXi host.

There is William Lam blog post "Copying files from a USB (FAT32 or NTFS) device to ESXi" describing how you can use USB with FAT or NTFS filesystem to transfer ISOs but it did not work for me, therefore I wanted to use VMFS filesystem for ISO files transfer. I have VMware Fusion on my MacOSX laptop so it is very easy to spin up VM with ESXi 6.7 and have network access (local within a laptop) to ESXi. I use USB stick connected to the laptop and passed through to VM with ESXi. USB disk is recognized by ESXi but the only challenge is to create VMFS datastore because web management (HTML5 Client) does not allow create new VMFS datastore on USB disks.

Som, the only way is to create it from the command line.

By the way, all credits go to the blog post "Creating A VMFS Datastore On A USB Drive" and here is a quick installation procedure based on the mentioned blog post.

STOP USB Arbitrator

/etc/init.d/usbarbitrator status
/etc/init.d/usbarbitrator stop
/etc/init.d/usbarbitrator status

Find USB disk name

vdq -q
esxcfg-scsidevs -l

echo $MYDISK

Create 10GB VMFS datastore on USB disk

partedUtil getptbl $MYDISK
partedUtil mklabel $MYDISK gpt
partedUtil showGuids
partedUtil setptbl $MYDISK gpt "1 2048 20000000 AA31E02A400F11DB9590000C2911D1B8 0"
vmkfstools -C vmfs6 -S E2USB-ISO-Datastore ${MYDISK}:1

So datastore E2USB-ISO-Datastore is created and you can use upload ISO files to datastore and it goes over the virtual network within laptop computer so it is pretty fast.

Datastore usage on real ESXi host

When ISO files are on USB datastore, you can gracefully shutdown virtual ESXi, remove USB disk from a laptop and connect it to physical ESXi system. USB Arbitrator on physical ESXi system must be temporarily disabled by command ...

/etc/init.d/usbarbitrator stop 

... otherwise, the disk would not be usable within ESXi host as a USB device would be ready for USB passthrough, which you do not want in this particular case. After data transfer to non USB datastore, you can remove USB disk and start USB arbitrator ...

/etc/init.d/usbarbitrator start 

Hope this procedure helps at least one other person in VMware virtual community.

What motherboard chipset is used in VMware Virtual Hardware?

Today I have been asked by one of my customers what motherboard chipset is used in VMware Virtual Hardware. The answer is clearly visible from the screenshot below ...

Motherboard chipset

Motherboard chpset is Intel 440BX (https://en.wikipedia.org/wiki/Intel_440BX). This chipset was released by Intel in April 1998. In the same year, VMware Inc. was founded.

The screenshot above was done in Windows 10 running as Guest OS in VM hardware version 13 but the same chipset is used for VM hardware version 14 so I would assume all VM hardware versions use the same chipset and difference among VM hardware versions are additional features like the maximum amount of RAM, number of NIC adapters, CPU features exposed from physical CPU to virtual CPU, etc.

On two pictures below you can see VM hardware difference between ESXi 3.5 and ESXi 4.0

ESXi 4.0

ESXi 3.5

Friday, March 01, 2019

VMware vSphere Memory Hot Add scalability limitation

VMware vSphere Hot Add CPU/Memory feature has specific requirements and limits. To mention some
  • Virtual machines minimum hardware is version 7.
  • It is not compatible with Fault Tolerance
  • vSphere Enterprise Plus license
  • Hot Remove is not supported
  • Hot-Add/Hot-plug must be supported by the Guest operating system (check at http://vmware.com/go/hcl)
  • Guest-OS technical and licensing limitations had to be taken into consideration.
However, it is good to know about another scalability limitation.

VMware has set a maximum value for hot add memory. By default, this value is 16 times the amount of memory assigned to the virtual machine. For example, if the virtual machine memory is 2 GB, the maximum value for hot add memory is 32GB (2x16).

Actually, this is a good safety mechanism and here is the reason for such restriction ...

When hot memory is enabled, the guest operating system uses a huge amount of kernel memory space in the PFN database. Windows operating system does not have dynamic PFN allocation. When adding memory to the virtual machine, to make it visible to the guest operating system, the PFN database needs to be dynamic as Windows lacks this feature.

Do you want to know more about "Page Frame Number (PFN) database"? Read this article.

This topic is documented in VMware KB https://kb.vmware.com/kb/2020846

Now there is another question. Does this limitation apply only to MS Windows or it applies to Linux OS as well? The short answer is yes it applies to Linux as well. However, for Linux OS there is another limitation. If you are running WM with Linux OS having less then 3GB RAM you can change the memory only up to 3GB RAM in total. If you need more. You have to power off VM, increase memory to for example 4 GB RAM and power on again. When you are running linux with more than 3GB you can use hot memory add but again with a limit to increasing it maximally 16 times.

Hope this is informative.

Memory Hot Add related VMware KBs:

Sunday, December 30, 2018

New Home Lab managed by containerized PowerCLI and RACADM

Christmas holidays are a perfect time to rebuild the home lab. I have got a "Christmas present" from my longtime colleague knowing each other from times when we were both Dell employes. Thank you, Ondrej. He currently works for local IT company (Dell partner) and because they did a hardware refresh for one of their customers, I have got from him 4 decommissioned, but still good enough, Dell servers PowerEdge R620 each having populated a single CPU socket and 96 GB RAM. The perfect setup for a home lab, isn't it? My home lab environment is the topic for another blog post but today I would like to write about containerization of management CLI's (VMware PowerCLI and Dell RACADM) which will eventually help me with automation of home lab power off / on operations.

Before these new Dell servers, I had in my lab 4 Intel NUCs which I'm replacing with Dell PE R620. Someone can argue that Dell servers will consume significantly more electrical energy, however, it is not that bad. Single PE R620 server withdraws around 70-80 Watts. Yes, It is more than Intel NUC but it is roughly just 2 or 3 times more. Anyway, 4 x 80 Watt = 320 Watt which is still around 45 EUR per month so I have decided to keep servers Powered Off and spin up them only on demand. Dell servers have out of band management (iDRAC7) so it is easy to start and stop these servers automatically via RACADM CLI. To gracefully shutdown all Virtual Machines and put ESXi hosts into maintenance mode and shutdown them I will leverage PowerCLI. I've decided to use one Intel NUC with ESXi 6.5 to keep some workloads up and running all times. These workloads are vCenter Server Appliance, Management Server, Backup Server, etc. All other servers can be powered off until I need to do some tests or demos in my home lab.

I would like to have RACADM and PowerCLI also up and running to manage Dell Servers and vSphere via CLI os automation scripts. PowerCLI is available as an official VMware docker image and there are also some unofficial RACADM docker images available in DockerHub, therefore I have decided to deploy PhotonOS as a container host and run RACADM and PowerCLI in Docker containers.

In this blog post, I'm going to document steps and gotchas from this exercise.


Photon OS is available at GitHub as OVA, so deployment is very easy.


The first step after Photon OS deployment is to log in as root with the default password (default password is "changeme" without quotation marks) and change root password.


By default, IP address is assigned via DHCP. I want to use static IP address therefore I have to change network settings. In Photon OS, the process systemd-networkd is responsible for the network configuration.

You can check its status by executing the following command:

systemctl status systemd-networkd

By default, systemd-networkd receives its settings from the configuration file 99-dhcp-en.network located in /etc/systemd/network/ folder.

Setting a Static IP Address is documented here.

I have created file /etc/systemd/network/10-static-en.network with the following content


NTP=time1.google.com time2.google.com ntp.cesnet.cz

File permissions should be 644 so you can enforce it by command
chmod 644 10-static-en.network

New settings are applied by command
systemctl restart systemd-networkd


It is always better to use regular user instead of root account having full administration rights on the system. Therefore, the next step is to add my personal account

useradd -m -G sudo dpasek

-m creates the home directory, while -G adds the user to the sudo group.

Set password for this user

passwd dpasek

The next step is to edit the sudoers file with visudo. Search for %sudo and remove the ‘#’ from that line. After that, you can log in with that account and run commands like a root with ’sudo ’. Please note, that sudo is not installed by default, therefore you have to install it by your self by a single command

tdnf install sudo

as described later in this post.


If you want to disable password expiration use command chage

chage -M 99999 root
chage -M 99999 dpasek


Photon OS by default blocks ICMP, therefore you cannot ping from outside. Ping is, IMHO, very essential network tool for troubleshooting, therefore it should be always enabled. I do not think it is worth to disable in the sake of better security. Here are commands to enable ping ...

iptables -A INPUT -p ICMP -j ACCEPT
iptables -A OUTPUT -p ICMP -j ACCEPT

iptables-save > /etc/systemd/scripts/ip4save


Photon OS package manager is tdnf, therefore OS update is done with command ..

tdnf update

if you need to install additional software you can search for it and install it

I have realized there is no sudo in the minimal installation from OVA, therefore if you need it, you can search for sudo

tdnf search sudo

and install it

tdnf install sudo


I'm going to use Photon OS as a Docker host for two containers (PowerCLI and RACADM) therefore I have to start docker daemon ...

systemctl start docker

To start the docker daemon, on boot, use the command:

systemctl enable docker


To run docker command without sudo I have to add linux user (me) to group docker.

usermod -a -G docker dpasek


I already wrote the blog post how to spin up of PowerCLIcore container here. So let's quickly pull PowerCLIcore image and instantiate PowerCLI container.

docker pull vmware/powerclicore

Now, I can remotely log in (SSH) as a regular user (dpasek) and run any of my PowerCLI commands to manage my home lab environment.

docker run --rm -it vmware/powerclicore

Option --rm stands for "Automatically remove the container when it exits".

To work with PowerCLI following commands are necessary to initialize PowerCLI configuration.

Set-PowerCLIConfiguration -Scope User -ParticipateInCEIP $true
Set-PowerCLIConfiguration -InvalidCertificateAction:ignore

The configuration persists within each container session, however, it disappears when the container is removed, therefore it is better to instantiate container without -rm option, configure PowerCLI configuration, keep the container in the system and start container next time to perform any other PowerCLI operation.

docker run -it -v "/home/dpasek/scripts/homelab:/tmp/scripts" --name homelab-powercli --entrypoint='/usr/bin/pwsh' vmware/powerclicore

Option --name is useful to set the name of the instantiated container because the name can be used to restart container and continue with PowerCLI.

Inside the container, we can initialize PowerCLI configuration and use all other PowerCLI commands, scripts and eventually exit from the container back to the host and return back by command

docker start homelab-powercli -i

In such approach, the PowerCLI configuration persists.


Another image I will need in my homelab is Dell RACADM to manage Dell iDRACs. Let's install and instantiate the most downloadable RACADM image.

docker pull justinclayton/racadm

and it can be used interactively and get system information from iDRAC with hostname esx21-oob

docker run --rm justinclayton/racadm -r esx21-oob -u root -p calvin getsysinfo


I would like to store all my home lab scripts in GitHub repository, synchronize it with my container host and leverage it to manage my home lab.

# install Git
sudo tdnf install git

# configure Git
git config --global user.name "myusrname"
git config --global user.email "mymail@example.com"

git clone https://github.com/davidpasek/homelab

# save Git credentials
git config credential.helper store


In case, I do not want to use PowerCLI interactively and run some predefined PowerCLI scripts then local script directory has to be mapped to the container as shown in the example below

docker run -it --rm -v /home/dpasek/scripts/homelab:/tmp/scripts --entrypoint='/usr/bin/pwsh' vmware/powerclicore /tmp/scripts/get-vms.ps1

The option -rm is used to remove the container from the system after the PowerCLI script is executed.

The option -v is used to do the mapping between container host directory /home/dpasek/scripts/homelab and container directory /tmp/scripts

I was not able to run the PowerCLI script directly with docker command without the option --entrypoint

The whole toolset is up and running so the rest of exercise is to develop RACADM and PowerCLI scripts to effectively managed my home lab. The idea is to shut down all VMs and ESXi hosts when the lab is not needed. When I will need the lab, I will simply power on some vSphere Cluster and VMs within these clusters having vSphere tag "StartUp".

I'm planning to store all these scripts in GitHub repository from two reasons
  1. GitHup repository will be used as a backup solution 
  2. You can track the progress of my home lab automation project
Hope I will find some spare time to finish my idea and automate this process which I have to do manually at the moment.

Related resources:

Tuesday, December 11, 2018

VMware Change Block Tracking (CBT) and the issue with incremental backups

One of my customers is experiencing a weird issue when using a traditional enterprise backup (IBM TSM / Spectrum Protect in this particular case) leveraging VMware vSphere Storage APIs (aka VDDK) for image-level backups of vSphere 6.5 Virtual Machines. They observed strange behavior on the size of incremental backups. IBM TSM backup solution should do a full backup once and incremental backups forever. This is a great approach to save space on backup (secondary) storage. However, my customer observed on some Virtual Machines, randomly created over the time, almost full backups instead of expected continuous incremental backup. This has obviously a very negative impact on the capacity of the backup storage system and also on backup window times.

The customer has vSphere 6.5 U2 (build 9298722) and IBM TSM VE They observed the problem just on VMs where VM hardware was upgraded to version 13. The customer opened a support case with VMware GSS and IBM support.

IBM Support observed VADP/VDDK API function QueryChangedDiskAreas was failing with TSM log message similar to ...

10/19/2018 12:04:26.230 [007260] [11900] : ..\..\common\vm\vmvisdk.cpp(2436): ANS9385W Error returned from VMware vStorage API for virtual machine 'VM-NAME' in vSphere API function __ns2__QueryChangedDiskAreas. RC=12, Detail message: SOAP 1.1 fault: "":ServerFaultCode[no subcode]
"Error caused by file /vmfs/volumes/583eb2d3-4345fd68-0c28-3464a9908b34/VM-NAME/VM-NAME.vmdk"

VMware Support (GSS) instructed my customer to reset CBT - https://kb.vmware.com/kb/2139574 or disable and re-enable CBT - https://kb.vmware.com/kb/1031873 and observe if it solves the problem.

A few days after CBT reset, the problem with backup occurred again, therefore it was not a resolution.

I did some research and found another KB - CBT reports larger area of changed blocks than expected if guest OS performed unmap on a disk (59608). We believe that this the root cause and KB contains workaround and final resolution.

The root cause mentioned in VMware KB 59608 ...
When an unmap is triggered in the guest, the OS issues UNMAP requests to underlying storage. However, the requested blocks include not only unmapped blocks but also unallocated blocks. And all those blocks are captured by CBT and considered as changed blocks then returned to backup software upon calling the vSphere API queryChangedDiskAreas(changeId).
Workaround recommended in KB ...
Disable unmap in guest VM.
For example, in MS Windows Operating Systems UNMAP can be disabled by command

fsutil behavior set Disable DeleteNotify 1 

and re-enabled by command

fsutil behavior set Disable DeleteNotify 0

Warning! Disabling UNMAP in guest OS can have a tremendous negative impact on storage space reclamation, therefore, fixing space issue in secondary storage can cause storage space issue on your primary storage. Check your specific design before the final decision on how to workaround this issue.

Anyway, the final problem resolution has to be done by the backup software vendor ...
If you have VDDK 6.7 or later libraries, take the intersection of VixDiskLib_QueryAllocatedBlocks() and queryChangedDiskAreas(changeId) to calculate the actually changed blocks.
The backup software should not use just API function QueryChangedDiskAreas but also function QueryAllocatedBlocks and calculate disk blocks for incremental backups. Based on VDDK 6.7 Release Notes, VDDK 6.7 can be leveraged even for vSphere 6.5 and 6.0. For more info read Release Notes here.

I believe the problem occurs only on the following conditions
  • The virtual disk must be thin-provisioned.
  • VM Hardware is 11 and later - older VM hardware versions do not pass UNMAP SCSI commands through
  • The guest operating system must be able to identify the virtual disk as thin and issuing UNMAP SCSI commands down to the storage system
Based on conditions above I personally believe, that another workaround to this issue would be to not use thin-provisioned virtual disks and convert them into thick virtual disks. As far as I know, thick virtual disks do not pass UNMAP commands through VM hardware, therefore it should not cause CBT issues.

My customer is not leveraging thin-provisioning on physical storage layer, therefore he is going to test workaround recommended in KB 59608 (disable UNMAP in Guest OS's) as a short-term solution and start the investigation of the long-term problem fix with IBM Spectrum Protect (aka TSM). It seems IBM Spectrum Protect Data Mover 8.1.6 is leveraging VDDK 6.7.1 so upgrade from current version 8.1.4 to 8.1.6 could solve the issue.