Tag Archive for VMware

VCP6-DCV Delta Exam (2V0-621D) Study Guide and Exam Experience


Having successfully completed the VCP6-DCV Delta Exam (2V0-621D) this week, I thought it would be worthwhile jotting down a few thoughts on the exam, and noting the resources I used to prepare for it.

I’ve previously completed the VCP3, VCP4 and VCP5 “DCV” exams, however being specifically a delta exam, this one was a little different. The exam primarily covers the differences between vSphere 5 and vSphere 6, with a handful of seemingly more general questions.

For summary impressions of the exam (i.e. the TLDR), jump to the end of this article! :)

I used the following resources in prep for the exam:


The Exam
The exam itself was different to any previous VCP exam I’ve done. I would say that because the scope of the exam was much narrower, the depth of the questions seemed to me to be significantly more, with a few really tricky ones thrown in there.

Over all if I was to do it again (and when it comes time to do the VCP7 in a few years) I would probably just do the full VCP exam, rather than the delta. That way you can be sure of a decent number of the easy peasy questions which will probably be on stuff you’ve been doing for years, as well as the new stuff you may not know quite as well.

Obviously having not done the full VCP6 exam I can’t say this for sure, but I would say it’s a pretty good bet.

NanoLab – Part 10 – Your NUCs are nice and cool, but what about your stick?


I have been running a variety of Intel NUC nodes in my vSphere homelab over the past 3 years now, including the D34010WYKH, DC3217IYE & DC53427HYE.

In that time I have unfortunately seen more than my fair share of USB drive failures and corruptions, generally with an error which looks something like this:

Error loading /k.b00
Fatal error: 33 (Inconsistent data)

These are not cheap and nasty, or freebie USB drives, so I would not normally expect to see this rate of failures. The error only occurs when you reboot the host, and the startup bombs out at the start of the hypervisor launch. I have often managed to recover the stick by copying back corrupted files from another instance, but generally I needed to rebuild and restore the image. An unnecessary pain in the rear!

The Root Cause
The NUC case can become quite warm during normal operation with or without the fans spinning up, and I have come to believe that the main reason for the corruptions is that the USB stick itself is getting too hot and therefore eventually failing. Having pulled a USB out from a recently shut down node, they are really quite hot to the touch. You don’t actually see the symptom / failure until a reboot because the ESXi image actually runs in memory, so is only loaded from the USB stick at boot time.

The Solution
As for the solution, it’s really quite simple. I purchased a number of 12cm (5 inch) USB 2.0 extender cables on eBay for just 99p each (including delivery!).

These keep the USB stick indirectly attached to the NUC chassis, and as such the heat does not transfer into the flash drive. Since doing this I have not seen any further issues with the corruptions. Job done!

Keeping things cool: USB extender on Intel NUC

Keeping things cool: USB extender on Intel NUC

Software Defined Storage Virtualisation – How useful is that then?

VMware Storage

Ignoring the buzzword bingo post title, storage virtualisation is not a new thing (and for my American cousins, yes, it should be spelt with an s! :) ).

NetApp have for example been doing a V-Series controller for many years which could virtualise pretty much any storage you stick in the back of it. It would then present it as NFS and layer on all of the standard ONTAP features.

The big advantage then was that you can use the features which might otherwise be missing from your primary or secondary storage tiers, as well as being able to mix and match different tiers of storage from the same platform.

In a previous role, we had an annual process to full backup and restore a 65TB Oracle database from one site to another over a rather slow link, using an ageing VTL that could just about cope with incrementals and not much more on a day to day basis. End to end this process took a month!

Then one year we came up with a plan to used virtualised NFS storage to do compressed RMAN backups, replicate the data using snap mirror and restore on the other side. It took us 3 days; an order of magnitude improvement!

That was 4 years ago, when the quantity of data globally was about 4x less than it is now; the problem of data inertia is only going to get worse as the worlds storage consumption doubles roughly every two years!

What businesses need is the flexibility to use a heterogeneous pool of storage of different tiers and vendors in different locations to move our data around as required to meet our current IT strategy, without having to change paths to data or take downtime (especially on non virtualised workloads which don’t have the benefits of Storage vMotion etc). These tiers need to provide the consistent performance defined by individual application requirements.

It’s for this reason that I was really interested in the presentation from Primary Data at Storage Field Day 8. They were founded just two years ago, came out of stealth at VMworld 2015, and plan to go GA with their first product in less than a month’s time. They also have some big technical guns in the form of their Chief Scientist, the inimitable Steve Wozniak!

One of the limitations of the system I used in the past was that it was ultimately a physical appliance, with all the usual drawbacks thereof. Primary Data are providing the power to abstract data services based on software only, presented in the most appropriate format for the workload at hand (e.g. for vSphere, Windows, Linux etc), so issues with data gravity and inertia are effectively mitigated. I immediately see three big benefits:

  • Not only can we decouple the physical location of the data from it’s logical representation and therefore move that data at will, we can also very quickly take advantage of emerging storage technologies such as VVOLs.
    Some companies who shall remain nameless (and happen to have just been bought by a four letter competitor) won’t have support for VVOLs for up to another 12 months on some of their products, but with the “shim” layer of storage virtualisation from Primary Data, we could do it today on virtually any storage platform whether it is VVOL compliant or not. Now that is cool!
  • By virtualising the data plane and effectively using the underlying storage as object storage / chains of blocks, they enable additional data services which may either not be included with the current storage, or may be an expensive add-on license. A perfect example of this is sync and async replication between heterogenous devices.
    Perhaps then you could spend the bulk of your budget on fast and expensive storage in your primary DC from vendor A, then replicate to your DR site asynchronously onto cheaper storage from vendor B, or even a hyper-converged storage environment using all local server media. The possibilities are broad to say the least!
  • The inclusion of policy based Quality of Service from day one. In Primary Data parlance, they call them SLOs – Service Level Objectives for applications with specific IOPS, latency etc.
    QoS does not even exist as a concept on many recent storage devices, much to the chagrin of many service providers for example, so being able to retrofit it would protect the ROI on existing spend whilst keeping the platform services up to date.

There are however still a few elements which to me are not yet perfect. Access to SMB requires a filter driver in Windows in front of the SMB client, so the client thinks it’s talking to an SMB server but it’s actually going via the control plane to route the data to the physical block chains. A bit of a pain to retrofit to any large legacy environment.

vSphere appears to be a first class tenant in the Primary Data solution, with VASA and NFS-VAAI supported out of the “virtual” box, however it would be nice to have Primary Data as a VASA Client too, so it could read and then surface all capabilities from the underlying storage straight through to the vSphere hosts.

You will still have to do some basic administration on your storage back end to present it through to Primary Data before you can start carving it up in their “Single Pane of Glass”. If they were to create array plugins which would allow you to remote manage many common arrays this would really make that SPoG shine! (Yes, I have a feverish unwavering objection to saying that acronym!)

I will certainly be keeping an eye on Primary Data as they come to market. Their initial offering would have solved a number of issues for me in previous roles if it had been available a few years earlier, and I can definitely see opportunities where it would work well in my current infrastructure. I guess it now becomes up to the market to decide whether they see the benefits too!

Further Reading
Some of the other SFD8 delegates have their own takes on the presentation we saw. Check them out here:

Ray Lucchesi – Primary data’s path to better data storage presented at SFD8

Dan Frith – Primary Data  Because we all want our storage to do well

Disclaimer/Disclosure: My flights, accommodation, meals, etc, at Storage Field Day 8 were provided by Tech Field Day, but there was no expectation or request for me to write about any of the vendors products or services and I was not compensated in any way for my time at the event.

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