Wednesday, 19 October 2011

Practical lessons - Fault Tolerant VM

I have read quite a few official docs and different bloggers' posts about VMware FT, but once again I got evidence that practical knowledge is a best way of studying.
FT seems to be amazing feature, but the long list of requirements and restrictions can stop most of the VMware enthusiasts. Nevertheless, FT is one of the topic of VCAP-DCA blueprint, so I spent half a day playing in my lab with FT and trying to enable FT just for one VM. 

I wrote down some important lessons I learned about it, even though they seem very obvious you need to have some practical experience to remember them forever :)
  • The identical CPU model are required - in my lab it didn't work on hosts that had Xeon 5550 and Xeon 5650
  • The identical patch/firmware level is required - the same here, hosts had different firmware versions
  • The VM Monitor mode has to be set to Use Intel VT-x/AMD-v for CPU virtualization and software for MMU Virtualization". - Yes, I have read that EPT and Large Pages are not supported for FT, but I didn't know it had to be switched off manually.
  • VM disk can be converted to thick-eager-zeroed one only when VM is shutdown. - I was quite sure it was doable while VM was running
  •  Memory reservation is set to the amount of configured memory. - You need to be very careful enabling FT if you use HA with HA Admission Control configured with hosts number to tolerate. This can impact the slot size of your HA cluster. 
  • It is possible to configure Hyperthreading Core Sharing mode to None to provide slightly better performance for FT VM. - Actually, I am not really convinced that it provides better performance for FT enabled VM, but at least it will guarantee no other vCPU will be scheduled with FT VM vCPUs on the same physical CPU. My main idea was to make sure it is compatible with FT. 
  • When you disable FT the secondary VM still stays in vSphere, but it powered off and disabled. All historical data about FT performance is kept.
  • When you turn off FT the secondary VM is removed and all historical data is delel.
  • RDM disks are not supported in FT VM.
I have also found some minor bug when you turn off FT. When you enable FT for VM it warns you about memory reservation and says it reservation will be maintained while FT is on. 

However, when I turned off FT the VM still kept memory reservation. Not a big deal, but it is just good to know you need to check VM settings after FT is switched off. 

There are a lot of other problems/issues you can face with when enabling FT, but my story was not that long :)

If you find this post useful please share it with any of the buttons below. 

Saturday, 8 October 2011

My VCP 5 Exam experience

One year ago I passed VCP4 exam. That was a tough adventure. In August 2010 I attended my training on vSphere 4.1 and it was my very first experience with virtualization technologies. 2 weeks after the training I built my first vSphere farm on new HP Blade servers and carried out my first migration from VI 3.5 to vSphere 4.1. It was a hard time for me - zero real life experience, lack of knowledge and understanding how all these technologies work. However, by October 2010 I was ready to take my first exam for VMware. The final score of exam was just a little bit higher than the passing score, but I was still happy since I fell in love with vSphere and virtualization world.

This year I have decided to take an exam without any hands on experience with vSphere 5 for the simple reason that I don't have free time to build a proper lab and play around with new features. All my time currently is devoted to a preparation for a VCAP-DCA lab. Since this preparation has been lasting for last 6 month I can say now I have a solid understanding of main vSphere technologies. Also, I have designed and built few small to medium size vSphere farms and gained some real life experience with vSphere. 

So, I have started with reading all "vSphere 5: What's New" documentation. After that I decided to take a mock exam on VMware site and then I found out that there were still some gaps in my vSphere 5 knowledge. Reading official documenation is not a big fun. Therefore I wanted to buy some good book that explains the new technologies in depth and, what is more important, provides examples of their practical implementations, which helps me a lot to memorize the material. Surprise-surprise, I found only one vSphere 5 book available on Amazon site, which is the great book by Duncan Epping and Frank Denneman, however it was not exactly what I wanted for VCP5 exam preparation. So, I had to go back to VCP 5 Blueprint and go through all links to official VMware documentation, which took me about a week. 

The exam was more difficult than I expected. I was actually a bit scared after I answered first 10 questions and wasn't sure if my answers were correct in 5 of them. I was surprised there were very few questions about configuration maximums and none about licensing. That was a bit frustrating as I have spent a lot of time in debates about new licensing model :)  Surprisingly, there were more  questions than I expected about vCenter appliance. I can definitely say this exam requires more real life experience with vSphere than VCP4. Good thing is that probably about 80% of exam material is inherited from VCP4 exam, therefore, if you feel confident in your expertise in vSphere 4 it shouldn't take you more than a week to go through blueprint briefly, focusing only on new features.  Additionally, I checked some popular virtualization blogs to get alternative view or interpretation of the particular feature and I really like reading implementation examples' stories.  

A day before exam I looked for more mock exams on the Internet and found some good links here. I would say all of them are not as difficult as the real one, but at least you can find out what your gaps in vSphere 5 knowledge are and gain some confidence in yourself :)

Now I can go back to my VCAP-DCA lab. I would like to wish a good luck for this exam to all of you who has the same passion for virtualization technologies as I have. :)

If you find this post useful please share it with any of the buttons below.