Vin8140_123VM
Contributor
Contributor

VMWARE Interview Questions

VM is not my forte other than the straight forward install from CD make some VM's on an ESX 3.02 server.

Can you folks in the communtity helpme put together an list of say 10-15 questions on VMware. (from simple to progressively harder) with a short answer after them?

I would appreciate very much, as I need to interview a few people tommorrow afternoon. Again any type of question that would help me spot out the obvious, and people jsut putting VM on thier resumes for the sake of it... Thx again !!!!

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36 Replies
weinstein5
Immortal
Immortal

A couple quick ones are:

1) ask about virtual SMP - when and why should you give a vm multiple vCPUs - part of their answer whould be that best pracrtice is to start with a single vCPU because of you can run into perfomance issues do to CPU scheduling

2) Ask what version of Linux kernel does ESX run - if they are truly experienced they should say ESX is not Linux and does not use a Linux kernel - and give them an extra poijnt if they explain that the service console runs a modified version of Red Hat Ent 3 -

3) Ask if they have a VCP - there are very few paper VCPs -

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bguthrie1
Contributor
Contributor

Ask about how HA works.

Is HA dependent on virtualcenter (Only for Install)

What is the Maximum Host Failure allowed in a cluster (4)

How does HA know to restart a VM from a dropped Host (storage lock will be removed from the metadata)

How many iSCSI targets will ESX support 8 for 3.01, (64 for 3.5)

How Many FiberChannel targets(256) (128 on Install)

What is Vmotion(ability to move running vm from one host to another)

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weinstein5
Immortal
Immortal

Another good one to ask - does HA use vmotion? the answer is no - vm stops and restarts on ESX other host

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vmroyale
Immortal
Immortal

Somewhere prior to your VMware questions, maybe ask each of them if they ever visit this site! Some of your candidates may be reading this....

Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com
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postfixreload
Hot Shot
Hot Shot

Ask what is the different when you use viclient connect to VC and directly to ESX server itself. When you connect to VC you manage ESX server via vpxa (Agent on esx server). Vpxa then pass those request to hostd (management service on esx server). When you connect to ESX server directly, you connect to hostd (bypass vpxa). You can extend this to a trobleshoot case, where connect to esx see one thing and connect to VC see another. So the problem is most likely out of sync between hostd and vpxa, "service vmware-vpxa restart" should take care of it.

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fusebox
Enthusiast
Enthusiast

You can also ask them if one could run 20gb RAM worth of 10 windows 2003 VM(s) when infact the esx host only has 13gb RAM...The answer should be yes...This is called over allocation and esx intelligently uses its transperant memory sharing technique for similar or like VMs (running same OS)...You can also ask to describe in short about memory ballooning also...

One more, what is the maximum swap size we can allocate for an esx host..Ans:1600mb as,a maximum of only 800mb of RAM can be allocated for COS/SC..Hence twice the size of COS/SC = Swap Size..

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Dave_Mishchenko
Immortal
Immortal

Your post has been moved to the Virtualization Technology & Industry forum

Dave Mishchenko

VMware Communities User Moderator

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Vin8140_123VM
Contributor
Contributor

Some good stuff here. I appriciate everyones intellectual Q's and A's. Keep them comming.. thx again

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chandlm
Expert
Expert

1) ask about virtual SMP - when and why should you give a vm multiple vCPUs - part of their answer whould be that best pracrtice is to start with a single vCPU because of you can run into perfomance issues do to CPU scheduling

I couldn't agree with this one more. Pretty important from my experience that many people just let the vCPUs get out of hand. Especially now with multicore...even though you have all those cores do you really need to give out more vCPUs? A quick explanation from them on how ESX schedules vSMP machines would be a good indicator of their understanding.

- Have you ever used Converter? If so what are some of the steps you might take before/after the conversion process to prepare the physical/virtual?

- Explain snapshots; how they work, when they should/should not be used, etc.

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MattG
Expert
Expert

When I have interviewed candidates for an open VMWare position, I avoided questions relating to specific numbers like Max this or that as anyone can memorize numbers. The problem that I find when interviewing, is that everyone's resume is fluffed up claiming that they can do all of things that you are looking for. The first thing I do is ask for specific examples how they (not their team) implemented the items listed. For example, if they claim to have upgraded from ESX 2.5 to 3.0 I would ask them the specific steps they took to do that and why. Also what issues did they run into and how did they resolve them. Their answer will immediately tell you if they are the real deal or not ("It was a long time ago and I don't remember the exact details..."). I would do this for every VM specific item of interest on their resume.

Hypotheticals work well. For example I would say you have a budget of X and no SAN or VM infrastructure. With X I want you to design the best infrastructure possible to meet these Y requirements. There is no right answer per se, but you want to see how the candidate thinks through the problem. If you the interviewer is fluent in VMWare it is easy to spot the posers.

For actual questions:

  • What was the most difficult VMWare related problem/issue you faced in a production environment and what were the specific steps you took to resolve it?

  • When was the last time you called VM Support and what was the issue?

  • What was the most performance intensive production app that you supported in VMWare and what were the some of the challenges that it posed?

  • How would you determine that a perf intensive app is a good candidate? Spefically what tools would you use to identify candidates. Specifically inside those tools what metrics would you use?

  • What is yor philosphy on how much of the data center can be virtualized? (If the interviewer wants max virutalization, but the interviewee is not convinced that this is a good idea, this could be a deal breaker)

  • What is your opinion on the vritualization vendors (MS vs VM vs Citrix vs etc) and why? (Just trying to figure out if the candidate is keeping up with this ever changing virtualization market)

-MattG

-MattG If you find this information useful, please award points for "correct" or "helpful".
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Rockapot
Expert
Expert

I beleive another good question would be to ask the candidate to briefly describe VST, VGT & EST mode and 802.1Q trunking. I say this because networking is such an important part of VMware implementations and on going support.., do you really want a VMware engineer working in your environment if they lack the knowledge of these concepts (unless of course they are only delegated with low level permissions for generic VM operations)

More information on these mode's can be found here: www.vmware.com/pdf/esx3_vlan_wp.pdf

Also ask the candidate to explain why one mode would be used as opposed to another?, remember that there can be numerous reasons for the use of different modes depending on your company/client's network, security policies etc..

If you are interviewing for a consultant role it would also be a good scenario to provide a brief overview of a fictional network and ask the candidate to do a whiteboard draft of how the network would be layed out if say the ESX servers have 6 NIC's or 8 NIC's etc.. etc...

Hope this helps

Carl

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JDLangdon
Expert
Expert

One more, what is the maximum swap size we can allocate for an esx host..Ans:1600mb as,a maximum of only 800mb of RAM can be allocated for COS/SC..Hence twice the size of COS/SC = Swap Size..

You can make the size of the swap partition as large as you have available disk space for. Granted ESX will only avail of the first 1600MB but it can be bigger.

Jason

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Rockapot
Expert
Expert

Just a follow up on this article.

When the postings started "vmroyale" stated that "Some of your candidates may be reading this...", which I completely agreed with.

I have since being interviewing for 4 x VMware/Citrix consultants for a global telecoms firm and I have to say that I am shocked at the amoonut of consultants who arrive at the interview with such poor VMware skills despite massive company names or their CV's, and "extensive" background knowledge of the VMware arena.

I have actually used others interview questions from this forum, and my own contributed questions and only 1 of the 7 candidates interviewed knew answers to these so I was surprised at the amount of VMware engineers not reading the forums.

I should note that the recruitment agency putting candidates forward is only putting them forward based on the contents of their CV so they can not really identify the candidates failings at that stage.

How these candidates "specialise" in virtualisation with out reading the forums is beyond me.., surely anyone specialising in the subject and completely interested in the technology would take the time to read the forums, even if they dont come accross issues, just out of interest to see what others are experiencing..

My 2 cents worth Smiley Happy

Carl

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JDLangdon
Expert
Expert

Just a follow up on this article.

How these candidates "specialise" in virtualisation with out reading the forums is beyond me.., surely anyone specialising in the subject and completely interested in the technology would take the time to read the forums, even if they dont come accross issues, just out of interest to see what others are experiencing..

I saw one job posting in the internet just yesterday and one of the required skills was "High level of visibility as an expert in the VMTN community preferred." This is the first time I've ever seen this but I'm not surprised. The first time I do when a resume crosses my desk listing the candidate as a VMware specialist is search these forums for the owners name.

________________________________

Jason D. Langdon

This space is for rent.

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Rodos
Expert
Expert

Now you have done it. Every man and his dog is going to now put a post in this thread to make sure they will get a job interview. In fact there will be some new internet startups where you can hire people to develop or mature a personality and rank on VMTN which they then sell off on ebay to job applicants. Then some trader will come up with a futures market into to the value of the different rankings, people will start to hedge on the future worth of "Master".

Seriously though. This is effectively a new market and there is lots of demand. Its the exciting and interesting job that everyone wants to get. You are not that surprised are you, that candidates are turning up with little experience and inflated resumes?

Rodos. Rodney Haywood.

P.S. Dear Mr Recruiter, if you have searched VTMN and found this post by entering my name then yes what my resume says is true. I do know this stuff. VMTN is a valuable resource. Smart people in a technology who are evangelists do invest their own time to assist and build the community, and these are the type of people you want to employ. Now go away and annoy someone else. We already have great jobs, SO STOP RINGING ME!

Rodos {size:10px}{color:gray}Consider the use of the helpful or correct buttons to award points. Blog: http://rodos.haywood.org/{color}{size}
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Rockapot
Expert
Expert

The fact that candidates put a post on a thread will by no means get them an interview. I am just surprised people sell them selves as "virtualisation consultants & vmware consultants" which this requires them to be on top of their game in the arena in which they specialise. If I was to interview a vmware engineer or technician then fine, by all means they do not require the indpeth skillset, but as a consultant you should.

Responding to the other query, I dont think that ranking on the forums plays a mojority stake part in the acceptance of a candidate for a role. Fine, there are a series of well respected consultants in the UK on these forums, some of which I have worked with (ZippyDaMCT), but.... you will find that some of these of permanent employee's just contributing (very valuable) content to the forum for others.

So in essense, yes, absolutely, I am very surprised that candidates turn up with little experience. There is plenty virtualisation work out there (London/UK in my instance). Candidates have no excuse if they rock up at an interview with a leading organisation trying to sell skills which they should already hold if they are expecting to land a role.

At the end of the day an applicant will be well evaluated in an interview anyway so rankings in community for the not so well known forum posters will not apply.., again, it just surprises me that candidates are going for "consultant" roles not knowing much on their subject Smiley Happy

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Rodos
Expert
Expert

it just surprises me that candidates are going for "consultant" roles not knowing much on their subject Smiley Happy

I think you failed to see the humour in my last post but I could not help doing it again. I think you may have just nailed the definition of consultant, hence making them qualified Smiley Happy Okay, I will stop now, back to the normal serious programming schedule. I shall be light hearted no more.

Rodos {size:10px}{color:gray}Consider the use of the helpful or correct buttons to award points. Blog: http://rodos.haywood.org/{color}{size}
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Rockapot
Expert
Expert

I noticed the humour Smiley Wink

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TomHowarth
Leadership
Leadership

Rod that is not fair, there are "Consultants" and there are Consultants, we all know the diference, there are also "Engineers and then Engineers" it is rife in all levels.

If you found this or any other answer useful please consider the use of the Helpful or correct buttons to award points

Tom Howarth

VMware Communities User Moderator

Tom Howarth VCP / VCAP / vExpert
VMware Communities User Moderator
Blog: http://www.planetvm.net
Contributing author on VMware vSphere and Virtual Infrastructure Security: Securing ESX and the Virtual Environment
Contributing author on VCP VMware Certified Professional on VSphere 4 Study Guide: Exam VCP-410
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