Hello and welcome to VMinstall. In this post I’ll share a list of 25 VMware interview questions that I have crafted to screen for the best talent to manage and support VMware vSphere.
Why is my list any different from the hundreds of others on the web?
Well, first of all, it’s not a VCP test brain-dump…
Secondly, these interview questions are carefully crafted to narrow the talent pool to the most qualified, not the most memorized.
These interview questions require hands on experience to answer!
VMware Technical Interview Questions
The list of questions below is intentionally broken up into 5 groups:
- System Requirements for ESXi 5.5
- ESXi 5.5 Installation
- System Requirements for vCenter
- vCenter Installation
- Managing vSphere Resources
These 5 groups will test for technical proficiency that an experienced VMware administrator will [or should have].
The list is also what I use when interviewing someone at an administrator level who will manage the day-to-day support, build, and provisioning of:
- ESXi hosts
- virtual servers
- virtual networks
- virtual storage
Note: This list of questions may also be used for screening vSphere Engineers or Architects.
System Requirements for ESXi
- Your company has a bunch of unused server hardware and you have been asked to build a vSphere environment. But before you start you want to make sure it is supported by the ESXi version you plan to install. Where would you find a list of hardware that is supported?
Answer: You would check the VMware Compatibility Guide http://www.vmware.com/resources/compatibility/
- Your hardware is on the compatibility list and now you need to know what the minimum CPU and memory requirement of an ESXi host when building a 64bit OS that will take full advantage of ESXi features ?
Answer: 2 CPU Cores and 8 GB memory (bare minimum)
- Before you start installing software what must be enabled in the server BIOS in order to run ESXi?
Answer: The NX/XD bit needs to be enabled.
- You also have an old pile of network adapters to choose from. Where would you find a list of network adapters (NIC) that are supported by the version of ESXi you are installing?
Answer: You would check the VMware Compatibility Guide (same link as above)
- One of the servers you found wasn’t on the list and now you have a problem that is causing ESXi to purple screen so you call VMware for support. What would happen if they found out your hardware was not supported?
Answer: When hardware is not supported there are known issues that will happen and VMware cannot help to resolve problems due to unsupported hardware.
Unpacking the ESXi hardware interview questions.
Why are these questions about server hardware important?
Since 2006 I have had the awful job of having to clean up behind admins that would build vCenter and ESX/ESXi on any hardware they found. I’m guilty of it myself!
This is not only a bad practice but it also leads to unplanned maintenance and costly outages that impact users and customers.
ESXi will run on just about any hardware but that doesn’t mean it should.
An experienced vSphere admin will know better than to waste time (and a costly license) trying to run a 64bit OS on a server that doesn’t support it.
ESXi Installation Qs
- You’ve done this a hundred times. What are 3 methods that can be used when doing an Interactive ESXi installation?
Answer: Boot from a CD/DVD, boot from a USB, and PXE boot from a deployment server on the network.
- After so many ESXi builds you have figured out a faster way to do the install using a script. What’s the main difference between an interactive ESXi installation and a scripted installation?
Answer: The interactive install will require you to follow along and fill in the configuration information whereas, in a scripted install, the configuration information will be queried from an unattended text file (boot.cfg). Note: ESXi uses a Kickstart installer similar to Linux.
- You can install ESXi in your sleep. What is the command to access the installer window on ESXi 5.5?
Answer: Shift+O will get you to the runweasel command prompt.
- Darn, one of your servers is not loading. What’s the first thing to double-check when having a problem installing ESXi?
Answer: Make sure the hardware clock is set to UTC and the NX/XD bit is enabled in the BIOS.
- You’ve typed this stuff in a million times. Name 5 of the 10 bits of information required when installing ESXi?
Answer: Keyboard Layout, VLAN ID, IP Address, Subnet Mask, Gateway, Pri DNS, Sec DNS, Host Name, Installation Location, Root Password.
Now let’s unpack VMware interview questions about ESXi Installations.
ESXi is actually easy to install and setup; however, problems do arise when there are different admins or teams building out environments that share the same network, storage, and server resources. It is very important to have a standard build process so all hosts are built the same way every time.
Finding a good vSphere admin who can follow your standard, someone who can answer these basic questions, is a good start.
System Requirements for vCenter
- You decided not to run the vCenter appliance. What’s the minimum hardware requirements for a vCenter 5.x server?
Answer: It depends on whether other vSphere services such as single sign-on, inventory service, and the database will be running on the same hardware with vCenter.
- You’re going to upgrade vCenter and the old vCenter is running on Windows Server 2003. What Windows Operating System is required for vCenter 5.x?
Answer: Windows 2008 SP2
- You’re creating a list of ports you need the network admin to open on the firewall. What is port 902 used for on vCenter?
Answer: Port 902 is the default port vCenter uses to send data to hosts managed by vCenter.
- The old vCenter was running MS SQL Express but you are building 10 ESXi hosts. What’s the difference between using MS SQL Server Express and MS SQL Server for vCenter?
Answer: MS SQL Server Express is for vSphere installations with up to 5 ESXi hosts and 50 virtual servers.
- Your new boss doesn’t like MS SQL and asked you to use Oracle. Does vCenter support Oracle 11c or 12c?
Answer: Yes, but the JDBC driver must be installed manually.
Let’s review vCenter Interview Questions.
vCenter is at the heart of vSphere and when it’s not properly setup there will be problems!
These problems may be as small as a frustrated admins who can’t access and support virtual servers from a central management console. Or as large as a full-blown outage and corruption of the vCenter database.
For example, if a vSphere clouds grows too fast the additional load on hardware and system resources can cause performance problems that in worst cases can require a complete rebuild of vCenter on bigger hardware. Fortunately, each ESXi host can be managed separately if central management via vCenter is lost.
An experience vSphere admin who can answer these questions will likely know this work-around.
Managing vCenter Resources
Before we dive into the final 10 questions I want to stress how important finding a team player that will work closely with storage and network admins really is.
Tip! Pay close attention for any sign that the person you are interviewing does not think he/she owns your vSphere Cloud!
Storage is everything!
- You’ve learned over the years there’s more to vSphere than server hardware. What other 2 resources are just as important as servers and need to be properly planned out when designing and building a vSphere Cloud?
Answer: Storage and network resources are crucial for all vSphere Clouds.
- VMware vSphere give you options. What are the 4 typical ways storage can be added to a vSphere?
Answer: Storage can be added via iSCSI, FC, NFS and local disk (including DAS).
- When setting up a new datastore how many VMFS file systems should be created per LUN?
Answer: The best practice is to only create 1 VMFS file system per LUN.
- What is the best plan for a storage failure that impacts multiple datastores?
Answer: Always have a backup of the VMs on a separate storage environment that can be used to restore the lost virtual servers.
- Your host is a beast, dual socket with 8 core CPUs and 192 GB of memory. How many virtual servers can be added to a 1TB datastore?
Answer: It depends on the size of the VMs and the performance of the storage. Higher performing storage can be filled to capacity but space should be left for data growth and snapshots. A datastore should never be allowed to fill up 100%.
Unpacking these VMware Storage Qs.
Managing storage in a vSphere is an important job that can get a junior vSphere admins in big trouble!
Regardless of the protocol (iSCSI, NFS, FC) it requires a certain skill set which only comes with time and experience. Every new ESXi hosts which is added to vSphere requires someone to know how to balance the workloads across various storage tiers: local disk, SATA, SAS and SSD (depending on the needs of the environments and applications).
Far too many new VMware admins have learned the hard way that “Not all storage is the same” and very quickly a junior admin can cause an outage on a business critical database server simply by vMotioning a VM to a datastore that looks empty.
Networking is everything, too!
- This is a tough VMware interview question created just for you. Name 4 things that happen on the VMkernel networking layer?
Answer: vMotion, IP storage (iSCSI/NFS), Fault Tolerance and Virtual SAN.
- You have a VCP so this should be an easy interview question. What are 2 ways a vSphere admin can separate traffic from distinct environments (ex. Production and test) on the same hosts.
Answer: Either by creating separate vSwitches using dedicated NICs or if NICs are not available by creating separate port groups using different VLAN IDs on the same vSwitch.
- True or false. A Distributed Virtual Switch is very much like a physical switch that detects which VMs are logically connects to each port and uses that information to forward network traffic. Hint: It is not used for monitoring and administration across a datacenter.
Answer: False. A Distributed Virtual Switch acts as a single switch across all hosts in a datacenter to provide centralized provisioning, administration, and monitoring of virtual networks.
- Another True or false. NIC teams are “normally” put in active/active mode to allow fail-over in the event of a hardware failure.
Answer: False again. NIC teams are normally put in active/standby mode to allow fail-over in the event of a hardware failure. You can use active/active but this would not be standard and would require port channeling at the physical switch.
- This is a trick question so think about it! How many physical NICs are needed in an ESXi hosts for hosting 25 virtual servers on iSCSI storage split between 2 diverse environments (web/app).
Answer: The answer is purely subjective. It depends on how much separation is needed for performance and the level of redundancy built into the design for hardware failure. At minimum, maybe 2 (1 for data and 1 for VMkernel) but more should be used.
And finally, let’s review the Network Questions.
Since 2007, I estimate 80% of all the VMware problems I have dealt with were network or storage related. That’s not to say it was the network or storage admins fault. No, in most cases it was the VMware admins fault for not communicating and properly calculating the requirements before he/she asked for IP addresses or storage LUNs.
Like I said in the beginning. These questions are not for practicing to take a VCP test. They are designed to gauge the level of experience someone who is applying for your VMware admin or engineer job has before you give them the keys to start managing your company’s jewels.
I hope these VMware interview questions have been helpful!
You don’t need to use them all … maybe asking one question from each group during the screening call to start and then have your technical team unload the rest during the face to face interview?
Also, if you noticed, I didn’t add any questions about managing VMs. It’s because someone who can answer most or all 25 VMware questions will surely have experience deploying and supporting virtual servers.
That’s not all. I’m sure your technical team will have a few whoppers of their own!
Reference: VMware vSphere Documentation
Need an experienced Pro to screen your VMware applicants? Contact me on LinkedIn!
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