Category Archives: vSphere

Configuring a Proxy in Photon OS

I’ve been playing around recently with VMware’s new Photon OS platform. Thanks to it’s incredibly small footprint and virtualization-specific tuning, it looks like an excellent building block for a custom appliance I’m hoping to build. To keep the appliance as small as possible, I used the minimal deployment and then planned to install packages as required.

After deploying the appliance, I hit a roadblock as the package management tool called tdnf couldn’t reach any of the repositories. This was expected as my home lab is isolated and I have to go through a squid proxy server to get to the outside world.

root@photon-machine [ ~ ]# tdnf repolist
curl#7: Couldn't connect to server
Error: Failed to synchronize cache for repo 'VMware Photon Linux 2.0(x86_64) Updates' from ''
Disabling Repo: 'VMware Photon Linux 2.0(x86_64) Updates'
curl#7: Couldn't connect to server
Error: Failed to synchronize cache for repo 'VMware Photon Linux 2.0(x86_64)' from ''
Disabling Repo: 'VMware Photon Linux 2.0(x86_64)'
curl#7: Couldn't connect to server
Error: Failed to synchronize cache for repo 'VMware Photon Extras 2.0(x86_64)' from ''
Disabling Repo: 'VMware Photon Extras 2.0(x86_64)'

When trying to build the package cache, you can see that the the synchronization fails to specific HTTPS locations over port 443.

After having a quick look through the Photon administration guide, I was surprised to see that there wasn’t anything regarding proxy configuration listed – at least not at the time of writing. Doing some digging online turned up several possibilities. There seems to be numerous places in which a proxy can be defined – including in the kubernetes configuration, or specifically for the tdnf package manager.

The simplest way to get your proxy configured for tdnf, as well as other tools like WGET and Curl is to define a system-wide proxy. You’ll find the relevant configuration in the /etc/sysconfig/proxy file:

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Using SDelete and vmkfstools to Reclaim Thin VMDK Space

Using thin provisioned virtual disks can provide many benefits. Not only do they allow over-provisioning, but with the prevalence of flash storage, performance degradation really isn’t a concern like it used to be.

I recently ran into a situation in my home lab where my Windows jump box ran out of disk space. I had downloaded a bunch of OVA and ISO files and had forgotten to move them over to a shared drive that I use for archiving. I expanded the disk by 10GB to take it from 40GB to 50GB, and moved off all the large files. After this, I had about 26GB used and 23GB free – much better.


Because that jump box is sitting on flash storage – which is limited in my lab – I had thin provisioned this VM to conserve as much disk space as possible. Despite freeing up lots of space, the VM’s VMDK was still consuming a lot more than 26GB.

Notice below that doing a normal directory listing displays the maximum possible size of a thin disk. In this case, the disk has been expanded to 50GB:

[root@esx0:/vmfs/volumes/58f77a6f-30961726-ac7e-002655e1b06c/jump] ls -lha
total 49741856
drwxr-xr-x 1 root root 3.0K Feb 12 21:50 .
drwxr-xr-t 1 root root 4.1K Feb 16 16:13 ..
-rw-r--r-- 1 root root 41 Jun 16 2017 jump-7a99c824.hlog
-rw------- 1 root root 13 May 29 2017 jump-aux.xml
-rw------- 1 root root 4.0G Nov 25 18:47 jump-c49da2be.vswp
-rw------- 1 root root 3.1M Feb 12 21:50 jump-ctk.vmdk
-rw------- 1 root root 50.0G Feb 16 17:55 jump-flat.vmdk
-rw------- 1 root root 8.5K Feb 16 15:26 jump.nvram
-rw------- 1 root root 626 Feb 12 21:50 jump.vmdk

Using the ‘du’ command – for disk usage – we can see the flat file containing the data is still consuming over 43GB of space:

[root@esx0:/vmfs/volumes/58f77a6f-30961726-ac7e-002655e1b06c/jump] du -h *flat*.vmdk
43.6G jump-flat.vmdk

That’s about 40% wasted space.

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VUM Challenges During vCenter 6.5 Upgrade

After procrastinating for a while, I finally started the upgrade process in my home lab to go from vSphere 6.0 to 6.5. The PSC upgrade was smooth, but I hit a roadblock when I started the upgrade process on the vCenter Server appliance.

After going through some of the first steps in the process, I ran into the following error when trying to connect to the source appliance.


The exact text of the error reads:

“Unable to retrieve the migration assistant extension on source vCenter Server. Make sure migration assistant is running on the VUM server.”

I had forgotten that I even had Update Manager deployed. Because my lab is small, I generally applied updates manually to my hosts via the CLI. What I do remember, however, is being frustrated that I had to deploy a full-scale Windows VM to run the Update Manager service.

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Debunking the VM Link Speed Myth!

** Edit on 11/6/2017: I hadn’t noticed before I wrote this post, but Raphael Schitz (@hypervisor_fr) beat me to the debunking! Please check out his great post on the subject as well here. **

I have been working with vSphere and VI for a long time now, and have spent the last six and a half years at VMware in the support organization. As you can imagine, I’ve encountered a great number of misconceptions from our customers but one that continually comes up is around VM virtual NIC link speed.

Every so often, I’ll hear statements like “I need 10Gbps networking from this VM, so I have no choice but to use the VMXNET3 adapter”, “I reduced the NIC link speed to throttle network traffic” and even “No wonder my VM is acting up, it’s got a 10Mbps vNIC!”

I think that VMware did a pretty good job documenting the role varying vNIC types and link speed had back in the VI 3.x and vSphere 4.0 era – back when virtualization was still a new concept to many. Today, I don’t think it’s discussed very much. People generally use the VMXNET3 adapter, see that it connects at 10Gbps and never look back. Not that the simplicity is a bad thing, but I think it’s valuable to understand how virtual networking functions in the background.

Today, I hope to debunk the VM link speed myth once and for all. Not with quoted statements from documentation, but through actual performance testing.

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Boosting vSphere Web Client Performance in ‘Tiny’ Deployments

In my home lab, I’ve been pretty happy with the vCenter Server ‘Tiny’ appliance deployment size. For the most part, vSphere Web Client performance has been decent and the appliance doesn’t need a lot of RAM or vCPUs.

When I most recently upgraded my lab, I considered using a ‘Small’ deployment but really didn’t want to tie up 16GB of memory – especially with only a small handful of hosts and many services offloaded to an external PSC

Although things worked well for the most part, I had recently been getting vCenter alarms and would get occasional periods of slow refreshes and other oddities.


One of two alarms triggering frequently in my lab environment.

The two specific alarms were service health status alarms with the following text strings associated:

The vmware-dataservice-sca status changed from green to yellow

I’d also see this accompanied by a similar message referring to the vSphere Web Client:

The vsphere-client status changed from green to yellow

After doing some searching online, I quickly found VMware KB 2144950 on the subject. Although the cause of this seems pretty clear – insufficient memory allocation to the vsphere-client service – the workaround steps outlined in the KB are lacking context and could use some elaboration.

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VM Network Performance and CPU Scheduling

Over the years, I’ve been on quite a few network performance cases and have seen many reasons for performance trouble. One that is often overlooked is the impact of CPU contention and a VM’s inability to schedule CPU time effectively.

Today, I’ll be taking a quick look at the actual impact CPU scheduling can have on network throughput.

Testing Setup

To demonstrate, I’ll be using my dual-socket management host. As I did in my recent VMXNET3 ring buffer exhaustion post, I’ll be testing with VMs on the same host and port group to eliminate bottlenecks created by physical networking components. The VMs should be able to communicate as quickly as their compute resources will allow them.

Physical Host:

  • 2x Intel Xeon E5 2670 Processors (16 cores at 2.6GHz, 3.3GHz Turbo)
  • 96GB PC3-12800R Memory
  • ESXi 6.0 U3 Build 5224934

VM Configuration:

  • 1x vCPU
  • 1024MB RAM
  • VMXNET3 Adapter (1.1.29 driver with default ring sizes)
  • Debian Linux 7.4 x86 PAE
  • iperf 2.0.5

The VMs I used for this test are quite small with only a single vCPU and 1GB of RAM. This was done intentionally so that CPU contention could be more easily simulated. Much higher throughput would be possible with multiple vCPUs and additional RX queues.

The CPUs in my physical host are Xeon E5 2670 processors clocked at 2.6GHz per core. Because this processor supports Intel Turbo Boost, the maximum frequency of each core will vary depending on several factors and can be as high as 3.3GHz at times. To take this into consideration, I will test with a CPU limit of 2600MHz, as well as with no limit at all to show the benefit this provides.

To measure throughput, I’ll be using a pair of Debian Linux VMs running iperf 2.0.5. One will be the sending side and the other the receiving side. I’ll be running four simultaneous threads to maximize throughput and load.

I should note that my testing is far from precise and is not being done with the usual controls and safeguards to ensure accurate results. This said, my aim isn’t to be accurate, but rather to illustrate some higher-level patterns and trends.

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VMXNET3 RX Ring Buffer Exhaustion and Packet Loss

ESXi is generally very efficient when it comes to basic network I/O processing. Guests are able to make good use of the physical networking resources of the hypervisor and it isn’t unreasonable to expect close to 10Gbps of throughput from a VM on modern hardware. Dealing with very network heavy guests, however, does sometimes require some tweaking.

I’ll quite often get questions from customers who observe TCP re-transmissions and other signs of packet loss when doing VM packet captures. The loss may not be significant enough to cause a real application problem, but may have some performance impact during peak times and during heavy load.

After doing some searching online, customers will quite often land on VMware KB 2039495 and KB 1010071 but there isn’t a lot of context and background to go with these directions. Today I hope to take an in-depth look at VMXNET3 RX buffer exhaustion and not only show how to increase buffers, but to also to determine if it’s even necessary.

Rx Buffering

Not unlike physical network cards and switches, virtual NICs must have buffers to temporarily store incoming network frames for processing. During periods of very heavy load, the guest may not have the cycles to handle all the incoming frames and the buffer is used to temporarily queue up these frames. If that buffer fills more quickly than it is emptied, the vNIC driver has no choice but to drop additional incoming frames. This is what is known as buffer or ring exhaustion.

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