Category Archives: Virtualization

Everything about Virtualization

Unable to Connect to the vCenter Inventory Service

My vCenter Web client popped up an error that said “Unable to connect to the vcenter inventory service : https://ip:10443


Remember, in vCenter 5.0, the inventory service is running as a separate service and not as part of the vcenter service. The inventory service works for the web client. It manages the web client inventory objects and property queries that the web client requests when a user is browsing it. The web client runs efficiently by only requesting queries that the user is seeing on their screen – this enhances user experience and navigation.

In vCenter 5.1 – the inventory service is a completely separate component than the vcenter and can be installed on a separate box itself.

In my case, as expected, the service was off and I started the service on the vcenter server. The issue was resolved.

VM Replication in ESXi 5.1

rjapproves QuickY (For the impatient like me!)

  • VMware introduced virtual machine replication in today’s ESXi 5.1 announcement.
  • Virtual machine replication replicates your primary virtual machine to another datacenter so you can quickly bring up your virtual machines in a disaster event at the primary site.
  • A virtual machine is copied to the other site, a full copy followed by changed block copies are done.
  • Intelligent copy where application and/or database consistency is maintained using Microsoft Volume shadow copy service(VSS)
  • Replication is free product and is added as a feature
  • Replication runs off a agent that comes with each hypervisor install and a vSphere Replication appliance that runs on each vcenter at per vcenter basis. As of now, its maximum of 10 appliances per vcenter supporting 500 virtual machine replications per site.
  • Replication can be done on a per virtual machine and per hard disk basis.
  • The target virtual machine will not power on if the primary (source) virtual machine is pingable by vcenter server and/or is still powered on.
  • Recovery vm once powered on will have to be manually connected to the network via the vcenter web console (one click action).


This is exciting, VMware finally takes up Microsoft’s Hyper-V challenge and offers replication as a free product add on for all of us to enjoy.

So what is vmware replication really all about? Think of vmware replication as basically having a clone of your virtual machine on another hypervisor which may or may not be on the same site. Ideally, the replication will occur from one physical site to another. The catch is that this clone is constantly being updated – aka – any changes in the source site are transferred to the target site depending on the interval for replication you set.

The hypervisor inherently has a agent and there is a vmware replication appliance per vcenter whose job is to receive replication data and also keep track of the statuses. A vCenter can have upto 10 maximum vmware replication appliances. I am not clear on the maximum virtual machines that can be replicated but it seems like there is a cap on 500 virtual machines per vCenter.

The way it works, in the web based vcenter portal, you simply enable replication by a click and choose a virtual machine to replicate to another datacenter hypervisor. You get to choose how often the replication is to run, basically a RPO for your virtual machine. VMware allows a low RPO of 15 mins to a maximum of 24 hours. You can also set the destination virtual machine to have its disks as thin as opposed to the thick disks at the primary site. This allows you to save storage space on the target site.

Once that is set, you are all done, the initial replication will be a complete copy of your virtual machine over the wire. Now if you have a huge virtual machine, you can choose to pre-seed it to cut down on replication time. You can either copy it/clone it to a usb storage or FTP and then pre-seed that at the destination. Once Pre-seed is done, only changed blocks are copied. Change block tracking, i believe, is automatically enabled and only blocks that are changed are copied over. Remember the VA Agent is responsible to send over changed blocks and these are received by the VMware replication appliance on the other end.


Some cool things you can do is specifically pick which disks in a virtual machine you want to replicate and which you choose not to. For instance you can have a designated disk as swap disk for a virtual machine and you may choose not to replicate that disk.

To failover the virtual machine you simply have to initiate it from the vcenter web client, however remember, failover will not work or will not be allowed if your primary vm is still powered on and/or vcenter can ping it. When the target virtual machine comes up, it will disconnected from networks. The idea is for an administrator to look at the target and then to connect it to the network and not to have them blindly power on. This is to prevent accidental power ons that may result in network conflicts if any could happen.

I am quite sure that VMware is using the Virtual Disk Development Kit(VDDK) to get this all to work. The host agents that come loaded with the ESXi 5.1 install on the box use the VDDK to attach/detach disks and also ship data over wire. There are no security issues as of today, and replication is pretty secure.

I don’t have specific details yet but I will add more as we play along.

Do comment if you have any more information or need to correct/add info.

VMware Announces no more vRAM Entitlements!

Lets not even debate the whole structure about the vRAM pricing but VMware at VMWorld just announced (a minute back) that there are no more vRAM license entitlements. No vRAM, no per vm licensing model. Only per socket model which makes a lot of things easier. This was received with a lot of applause!

My First OpenStack Alamo Installation

This week, after I was able to create the containers, I had my first taste of Alamo deployed on my home environment.  I will write down step-by-step installation process in the next blog. The Alamo installation is very easy and comparable to ESX + a few extra options about passwords and networks.

Below is a screen shot of the console how it would look. Pretty similar to vmware’s ESX(i).
Also a really interesting article about Cloud computing, if you are trying to understand what it really and truly means is below. Its a 2009 article but gives you a decent idea about what its about.

Deploying OpenStack Alamo in a Nested ESX(i) box to test

So its exciting news that Rackspace has gone Open Cloud. However, very few of us have the luxury to run Open stack on its own dedicated controller/compute nodes, although an all-in-one configuration can be run. For instance, in my home lab, I am running it now as a nested hypervisor because that will allow me ample flexibility to get to know it.

If you are running vmware ESX(i) then you are in luck as the doc lists all the changes that you will need to do to the vm container in order to get OpenStack Alamo to run. Cody’s instructions on how to get the container ready helped greatly.

However, I have the OVA’s in here so you can download them. These containers, one for controller and the other for the compute node, have been preset with all changes necessary so your OpenStack Alamo installation will boot up with no issues. They are only 78KB each because they are empty containers 🙂 So clone them to multiple compute nodes as needed 🙂

Remember to change the cpu/ram/disk sizes as necessary. I marked disks as thin but if you have tons of disk to play with then you may delete and recreate it. These are empty containers and you can boot them up to the Alamo iso or cdrom.

Controller-Node – Download Here (78KB)

Compute-Node – Download Here (78KB)

Let me know if you run into problems!

How big is a snapshot by default?

So, I have been in the dark. (I attached a random pic not really of a snapshot :D)

I was under the impression that the snapshot in vmware – when a snapshot a snapshot is created will only be a few megabytes. Well I was wrong!
When a snapshot is created – the .vmsn which is the snapshot state file and stores the running state of the virtual machine – aka its RAM. So this will be = to the size of the RAM that is set for the virtual machine.
So if a virtual machine is with 16GB of RAM – then the .vmsn file which is created in a snapshot will be of that size 16GB!
Needless to say , the snapshot file which is the <vname>-Snapshot<###>.vmsn grows with the snapshot.

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