If you are working in IT (Information Technology) you probably know about Computer Virtualization. Computer Virtualization simulates physical servers through software technology and is an important part in today’s data center world. Virtualization is a fairly new technology and real specialists are hard to find. Accordingly salaries for these specialists easily reach 6 figures per year. The leading software provider in this field is VMWare.
But if you are a manager going to hire one of these specialist you want to make sure the candidate is really an expert in this field. And if you are a job candidate you want to make sure you know what to expect during a technical interview where you can expect VMWare interview questions. In my case I do have about 7 years of experience with computer virtualization and for the matter of this article I went out for a few interviews where companies were looking for virtualization specialists. To a certain degree I have to say I was shocked a little bit due to the lack of technical question in several interviews. I could tell that some of the hiring managers were scrambling to fully understand the technology and instead of preparing for a technical interview they skipped important parts of the technical interview all together. I actually received a few offers from these interviews, but politely declined them because none of offered jobs felt right.
So, what kind of technical questions should be part of a VMWare Virtualization related interview?
The questions should be a sample of simply verifying a good understanding of the technology and then deep-dive into situations either the company or the applicant has experienced and where the person interviewed can describe how the knowledge was applied or would be applied. This combined with the remaining part of the interview should provide a good insight in how good or bad a candidate is.
Believe it or not, but some so-called specialists have major problems with even the basics of virtualization and even simple questions will throw them off the chart. Here are some technical VMWare interview questions – going from easy to difficult.
1) Q.: What is HA and how does it work? A: HA = High Availability. HA kicks in (as an example) if a cluster node (ESX/ESXi host) goes down unexpectedly. HA will grab the virtual machines that were on that specific host and will move them to other hosts in the associated cluster and then power them on again. Of course there is a little more to this magic, but that is basically what it comes down to.
2) Q.: What do you use for scripting and automation for VMWare? A.: PowerCLI. PowerCLI is a special library of commands that runs on top of PowerShell. You were able to run shell scripts against ESX as ESX is running a Linux kernel under the hood. vSphere ESXi is Hypervisor only and the preferred method is PowerCli. Again, there is a little more to scripting and VMWare, but if you are a manager this type of question can easily be expanded if you are interviewing the right candidate. If you are an applicant, this question gives you a great foundation to shine and to show off with your scripting skills.
3) Q.: What are the licensing differences between vSphere 4 and vSphere 5? And why do they matter? A.: The most important licensing change between vSphere 4 and vSphere 5 is that besides having to license each physical CPU, each license is now tied to a certain memory (RAM) allowance. In the past customers kept the number of physical servers small and loaded them up with a lot RAM. Now VMWare “punishes” this strategy by giving each license a memory limitation. As a result customers with servers that were loaded with RAM will have to purchase additional licenses to match physical RAM to licenses. This also means a change in strategy for VM deployments. It is much more critical now to keep an eye on how much RAM is assigned to each VM, because over-subscribing memory can become expensive under the new licensing terms. As a manager asking this question you also want to hear that VMWare allows you to link vCenter installations together and to create over-lapping memory pools.
4) Q: What is the difference between a thin provisioned disk and a thick provisioned disk? A.: The short answer is that a thick provisioned disk takes up the entire disk space it is configured for. So, if you provision a 100 GB for a VM, it would take up 100 GB of actual disk space even if the virtual hard drive has only 15 GB of data in it. If the same disk is thin provisioned for 100 GB, then the VM operating system would show a 100 GB hard drive, but the actual size on the physical disk would only be 15 GB. Thin provisioning virtual disk is a great way to get better usage out of physical storage because in most cases hard drives assigned to VMs will never use all the assigned disk space. However, using thin provisioned disks requires the administrator to have tight monitoring of the storage system in place because if those VMs would suddenly use up all the disk space, it can cause a catastrophic event if the LUN runs out of physical disk space. Again, this question should give the hiring manager a good insight into the skills of the applicant. The applicant on the other side can expand this question and go into much more detail and shine with knowledge.
5) Q.: What is the difference between VMFS-3 and VMFS-5? A.: If a candidate does not know what VMFS is, then the interview should end right that moment. VMFS is the file system that ESX/ESXi uses on the storage LUNs. A few years back with ESX 3.0 VMWare introduced VMFS-3 and migrating up from VMFS-2 to the newer version was a little complicated and caused a lot of headaches. Migrating from VMFS-3 to the new VMFS-5 is much easier and can be done non-interruptive for the virtual machines. With VMFS-5 VMWare removed the need for different block size settings on the storage LUNs. In the past the block size had to be pre-configured in expectation of how large virtual disks on that LUN would eventually be. If the block size was set too small, larger VMDKs could not be deployed to that LUN accordingly. The new standard block size is 1 MB for VMFS-5 and it allows for any VMDK size within the (still) existing 2 TB limit (for VMDKs). VMFS-5 also allows for LUNs larger than 2 TB. It is also important to note that just converting an existing LUN with VMs on it, will not enable the new benefits of VMFS-5 for those VMs. The recommended way is to create a new empty LUN with VMFS-5 as the file system and then to migrate (storage vmotion) the existing VMs to this new LUN.
This is part #1 of VMWare Interview Questions for hiring managers and applicants. I will update this article with more information about many other VMWare interview questions over the next few days. Also, if you are a job seeker looking to land a gig as a VMWare admin, please do not consider these questions as a guide to land a high paying job without actually knowing the correct answers in more detail. It will become very obvious if you are cheating your way into a position. Employers will discover very quickly if you know your stuff or not. These VMWare interview questions are meant to be a helpful guide to prepare for an upcoming interview and to brush up knowledge in areas that you might have overlooked in the past.
Coming soon: VMWare Interview Guide for Job Seekers and hiring managers – published on Amazon Kindle. Please like this article on Facebook so that I can keep you up to date about the final publication date.
Quick update #1: I am about half-way done with the new VMWare Interview guide for job seekers and hiring managers. The eBook will not be a cheat sheet that will get you a job as a VMWare admin, but it will provide a great way of preparing for a technical interview. The ebook will contain standard technical questions as well as scenario-based questions. The ebook will be separated into sections for beginner level interviews, mid-level interviews, and senior level interviews. I will post more updates as the ebook progresses.