Archive for 28th March 2012

VMware VCAP-DCD 4 Exam Review

Well I’m very pleased to say that as of 4pm yesterday I am now a VCAP having passed the VMware VCAP4-DCD exam! So how was it?

My final week was an interesting one as I was actually out of office all week attending the internal/partner version of our Sun Storage 7000 Unified Storage System Installation, Maintenance and Administration course. In some ways this was a blessing as this was away from work (and all the distractions thereof), but studying all day on one subject then coming home at night and hammering the books on another does tax the brain somewhat!

Anyway, my final week of prep looked something like this:

One week to go: Finished watching the last few VMworld 2010 videos listed in my Exam Prep post. Mainly concentrating on the Exchange, SQL & Oracle ones, plus anything to do with SRM. I also watched several of the customer case studies, which were really useful in helping to relate the theory to the practice.

4 days to go: Watched all of the VCAP Brown Bags by Alastair Cooke et al, and the other two by Jason Boche and Harley Stagner. I cannot recommend these highly enough, and would really like to thank them for all of their efforts in producing this excellent (and completely free!) content. I would suggest you save these for your final week or so, as they are a great recap of everything you should know, plus a few extra golden nuggets. The one by Harley Stagner was also really good as an exam prep as the way things are discussed, is exactly what you need to do in your own head during the trickier exam questions! Do NOT miss this brown bag!

3 days to go: Read through all of my copious notes (> 400 pages of A4!!!) taken over the past 8 weeks. My preferred study method is always to take lots of notes as I watch / read material, and the act of writing it down helps to cement it, and give you a summarised reference for later. It does mean I tend to take a lot longer to watch a video as I often have to pause to write up diagrams etc (+30-50% on the length of most videos!). Obviously this is just my preference, but try it, and see if it helps you too…

2 days to go: Read the official VMware vSphere: Design Workshop [V4.x] workbook from my course last year, cover to cover. This didn’t really come up with anything I didn’t already know but it was good to remind me of the VMware-specific terminology, which obviously carries through to the blueprint and hence exam. In much the same way as you do with an MS exam, you have to “think with your VMware hat on”, even if you would do something slightly differently in the real world.
Finished reading VMware vSphere 4.1 HA and DRS Technical Deepdive by Duncan Epping and Frank Denneman, which is an excellent resource. If you don’t have time to read it all before your exam, just jump to Appendix A, which lists all of the key best practices (or recommended practices as Scott Lowe calls them!). If you are studying for the VCAP 5, there is an updated version already out: VMware vSphere 5 Clustering Technical Deepdive

Day before the exam: Read through a handful of the white papers dealing with the “fringes” of my knowledge, e.g. vCenter Heartbeat, where I haven’t actually used the product before, and where none of my previous study materials had covered much detail.
Read through the case study at the end of VMware vSphere Design by Forbes Guthrie, Scott Lowe and, Maish Saidel-Keesing. I read the book weeks ago, but deliberately saved the case study until later. In hindsight it may have been interesting to write down some thoughts on it before and after the rest of my study, maybe highlighting the things I’d learned in between!
Did as much of the VMware workshop case study as I had time left to complete. Went to bed @ 2.30am ready for my midday exam the next day.

Night before the exam, 4.30am: Got called out for work!!! Aaaargh! Not only that but it turns out it was due to someone being unable to connect an box by IP and thinking it was down, when they simply had the wrong IP… we invented DNS 30 years ago, let’s try using it!!! *facepalm*

The Exam: So as for the exam itself, I managed to completed every one of the 113 questions in time, but by “in time” what I actually mean is that I literally submitted my last answer with one second to go! The timing on the exam really is that tight! It didn’t help that about half way through the exam I needed the loo, and held on to the end. Had I not done so I might not have managed to get to those last handful of questions… the “crossing of legs” best practice was implemented with no DR plan, which I admit was a high risk strategy!

One thing I would say if looking at the exam with a critical eye, is that VMware should consider taking a small leaf out of Microsoft’s book. At the end of an MS exam you get a breakdown of where you gained all of your points (just a bar chart with a relative %). I would love to have known how my points were broken down so it could identify any weaknesses in my skill set, both for future exams and my actual job! Similarly there could be a small breakdown of the “relative” scores for the three types of questions. It’s great to know I passed, but would be even better to know where I didn’t do so well. This would be even more useful for people who don’t pass on the first attempt.

Regarding the “Visio tool”; even though I did actually do the demo a couple of times, I still had some issues with it, including the fact that the more objects you add, the more lag you experience (sometimes several seconds to place an object), which wastes precious time. I hope this improves with the vSphere 5 exam (though I doubt it will).

Now, a few tips for the actual exam from my perspective (obviously being careful not to breach the NDA!). Watch this brownbag with Jon Hall (of the VMware cert team) for an in depth look at the way the points are allocated per question, or see my summary:

  1. Don’t pay too much attention to the clock, except when doing the Visio design questions, and maybe for the final 30 minutes or so. Whenever I had one of those (for which VMware recommends 15 mins each), I checked the clock and worked out roughly what time I should be done by. A couple of them took me 5+ mins longer than the recommended time, but the others took slightly less so I guess it probably averaged to 15 or just over. Dont stress if one takes you a bit more time, but don’t let it go much beyond the 20 minute mark. At that point you’re better to move on and get more points elsewhere as you can still get lots of points for a “nearly right” answer.
  2. There was one exam strategy I mentioned in my prep post which came from a VMware trainer; Do all multi choice questions first. Second time through, do drag and drop questions. Third time through do design questions, which means you know how much time you have left.
    I did not take this approach in my exam, and instead just went through the exam in a serial fashion. If I had taken the above approach I may have wasted time with the review process to get back and not had enough time to complete the questions.
  3. Read the question before you read the information as it will help you to more quickly identify what information you are looking for and will reduce the likelihood of having to re-read anything.
  4. Once you have entered an answer don’t second guess yourself. Chances are your gut reaction is probably right as long as you have read the question and answers properly.
  5. Mark any questions you haven’t been able to complete but always put an answer in and keep moving. There are 113 questions to get through! If you do actually make it to the end with time to spare you can come back, but concentrate on getting through the questions first.
  6. I don’t believe there is negative marking employed, so any answer is better than leaving blanks. This is especially true if you reach the last 5 mins and still have some questions left. Speed read and answer quickly…

One final point I would make is that as I understand it, the VCAP4-DCD and the VCAP5-DCD are not massively different, just the new improvements which will tweak your designs (especially HA!) and the way the new blueprint emphasizes the design method. Therefore a very large proportion of the exam prep materials in my VMware VCAP-DCD 4 Exam Prep Guide should be just as relevant as a VCAP-DCD 5 exam prep guide. I plan to upgrade my VCAP4 to a VCAP5 while the information is still fresh in my mind. Hopefully this will be soon as the beta completed over three weeks ago, meaning the final exam version shouldn’t be far off.

In the mean time, I have to learn Hyper V for an upcoming project!…

Related posts:
VMware VCAP-DCD 4 Exam Prep Guide

propertyCollector Error When Editing Virtual Machine Swapfile Location

Today I came across the following propertyCollector error message whilst trying to modify the VM Swapfile location for two hosts in my lab cluster. This pops up as soon as you select the Virtual Machine Swapfile Location settings under the Configuration tab for your host. Once you click Close, you then see Swapfile Location: as Getting Data… for an infinite period of time, and the Edit… option becomes greyed out and cannot be selected.

The same error occurred on both an ESX and ESXi host in the came cluster, both using the latest vSphere 4.1 build 582267. I am going to assume this can appear on older versions too.

The object has already been deleted or has not been completely created

Call "PropertyCollector.RetrieveContents" for object "propertyCollector" on vCenter Server "<servername>" failed.

You can see the error in the following screenshot:

Call "PropertyCollector.RetrieveContents" for object "propertyCollector" on vCenter Server "<servername>" failed.

This seems to occur because the host does not have any record, even a default, for the snapshot location. This only affected half the hosts in my cluster, where the other half were showing their defaults just fine.

The fix for this is very simple. I’m sure it could be implemented by multiple methods, but I used PowerCLI. Simply:

  1. Connect to the faulty host, e.g.:
    Connect-VIServer <servername / ip>
  2. Validate that you can see your preferred datastore from that host:
  3. Manually set the datastore to your preferred DS:
    Set-VMHost -VMSwapfileDatastore <datastorename>
  4. Go back to vCenter and you will find the new value reflected, and you can now edit the Virtual Machine Swapfile Location settings under the Configuration tab for your host:

If you have multiple hosts with the same issue, or indeed when simply making swapfile location changes across your cluster, you could of course script the above.

I’m not sure whether this applies to vSphere 5 as I have not come across it there to date.

FreeNAS 0.7.2 NFS and iSCSI Performance in a vSphere 4.1 Lab

While doing some lab testing and benchmarking for my upcoming VCAP-DCD exam I came across some interesting results when messing about with NFS and iSCSI using FreeNAS. I plan to re-run the same set of tests soon using the EMC Celerra simulator once I have it set up.

The results are from very simplistic testing using a simple buffered read test only (it would be reasonable to expect write times to be the same or slower, and this is just a quick test for my own info). For this I used the following sample hdparm command in some Ubuntu VMs:

sudo hdparm -t /dev/sda

A sample output from this command would be:

/dev/sda:  Timing buffered disk reads: 142 MB in  3.11 seconds =  45.59 MB/sec

As this was a quick performance comparison I only repeated the test three times per storage and protocol type, but even with this simplistic testing the results fairly conclusive.

Test HW was based on my 24GB RAM ESX and ESXi cluster in a box solution [hence some results will be faster than you can achieve over a gig network as this is all running on one host] running under Windows 7 64-bit with VMware Workstation 8. Components are:

  • 4x ESX/ESXi 4.1 hosts running in Workstation 8 with an SSD datastore. 4GB RAM and 2x vCPUs each.
  • 1x FreeNAS 0.7.2 instance running in Workstation 8 with an SSD datastore and a SATA datastore. I use this over FreeNAS 8 as it has a significantly smaller memory footprint (512mb instead of 2GB). 1vCPU and 512 MB RAM.
  • 64-bit Ubuntu Linux VMs running nested under the ESX(i) virtual hosts. 1vCPU and 512 MB RAM each.

Storage components are:

  • SATA 2 onboard ICH10R controller
  • 1x Crucial M4 128GB SSD (500MB/sec Read, 175MB/Sec Write)
  • 1x Seagate 250GB 7200RPM SATA

The results of the testing are as follows:

Protocol Storage Type Read MB/sec
Local VMFS SSD 383
Local VMFS SATA 88
FreeNAS 0.7.2 w/ NFS SSD 11
FreeNAS 0.7.2 w/ NFS SATA 5
FreeNAS 0.7.2 w/ iSCSI SSD 175
FreeNAS 0.7.2 w/ iSCSI SATA 49

As you can see, FreeNAS with NFS does not play nice with ESX(i) 4. I can confirm that I have seen stats and posts confirming these issues are not aparent in the real world, with NetApp FAS or Oracle Unified Storage (which is aparently awesome on NFS) but for your home lab, the answer is clear:

For best VM performance using FreeNAS 7, stick to iSCSI!

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