Lets answer the impact/overhead portion first, yes there is an overhead. It is in the range of percents. You might ask yourself where this overhead is coming from and if that is vSphere overhead or… When CPU and Memory Hot-add is enabled the Guest OS, especially Windows, will accommodate for all possible memory and CPU changes. For CPU is will take the max amount of vCPUs into account, so with vSphere 5 that would be 32. For memory it will take 16 x  power-on memory in to account, as that is the max you can provision . Does it have an impact? Again, a matter of percents. It could also lead to problems however when you don’t have sufficient memory provisioned as described in this KB by Microsoft: http://support.microsoft.com/kb/913568.

Another impact, mentioned by Valentin (VMware), is the fact that on ESXi 5.0 vNUMA would not be used if you had the HotAdd feature enabled for that VM.

What is our recommendation? Enable it only when you need it. Yes they impact might be small, but if you don’t need it why would you incur it?!

I checked if there was a snapshot on the disk but that wasn’t the case. I tried the same thing on a different VM and it actually wasn’t greyed out. Then I noticed the difference between the VMs… The VM on which it was greyed out had an “IDE” disk and the other VM had a “SCSI” disk. It appears that it is currently not possible to change the size of an IDE virtual harddisk within vCenter.

My question of course was doesn’t this impact performance? The answer was simple: No as a limit on a vCPU is only applied when there’s a resource constraint. It took me a couple of minutes to figure out what he actually tried to tell me but basically it came down to the following:

When a single VM has a limit of 300MHz and is the only VM running on a host than it will run it full speed as it will be constantly rescheduled for 300MHz.

However, that’s not what happens in my opinion. It took me a while to get the wording right but after a discussion with @frankdenneman this is what we came up with:

Look at a vCPU limit as a restriction within a specific time frame. When a time frame consists of 2000 units and a limit has been applied of 300 units it will take a full pass, so 300 “active” + 1700 units of waiting before it is scheduled again.

In other words applying a limit on a vCPU will slow your VM down no matter what. Even if there are no other VMs running on that 4 socket quad core host.

Would I ever recommend setting a limit? Only in very few cases. For instance when you have an old MS DOS application which is polling 10000 times a second it might be useful to limit it. Personally witnessed they can consume 100% of your resources, unnecessary as it isn’t doing anything actually.

In most cases however I would recommend against it. It will degrade user experience / performance and there is no need in my opinion. The VMkernel has got a great scheduler which will take fairness into account.

• mbralign by NetApp(*)
• vOptimizer by Vizioncore(*)
• GParted(Free tool, Thanks Ricky El-Qasem).

First let’s explain why alignment is important. Take a look at the following diagram:

In my opinion there is no need to discuss VMFS alignment. Everyone, and if  you don’t you should!, creates their VMFS via vCenter which means it is automatically aligned and you won’t need to worry about it. However you will need to worry about the Guest OS. Take Windows 2003, by default when you install the OS your partition is misaligned. (Both Windows 7 and Windows 2008 create aligned partitions by the way.) Even when you create a new partition it will be misaligned. As you can clearly see in the diagram above every cluster will span multiple chunks. Well actually it depends. I guess that’s the next thing to discuss but first let’s show what an aligned OS partition looks like:

I would recommend everyone to read this document. Although it states at the beginning it is obsolete it still contains relevant details! And I guess the following quote from the vSphere Performance Best Practices whitepaper says it all:

Src
The degree of improvement from alignment is highly dependent on workloads and array types. You might want to refer to the alignment recommendations from your array vendor for further information.

Now you might wonder why some vendors are more effected by misalignment than others. The reason for this is block sizes on the back end. For instance NetApp uses a 4KB block size (correct me if I am wrong). If your filesystem uses a 4KB block size (or cluster size as Microsoft calls it) as well this basically means every single IO will require the array to read or write to two blocks instead of 1 when your VMDK’s are misaligned as the diagrams clearly show.

Now when you take for instance an EMC Clariion it’s a different story. As explained in this article, which might be slightly outdated, Clariion arrays use a 64KB chunk size to write their data which means that not every Guest OS cluster is misaligned and thus EMC Clariion is less effected by misalignment. Now this doesn’t mean EMC is superior to NetApp, I don’t want to get Vaughn and Chad going again , but it does mean that the impact of misalignment is different for every vendor and array/filer. Keep this in mind when migrating and / or creating your design.

source

Products that have passed the SVVP requirements for Windows Server 2008 R2 are considered supported on Windows Server 2008, Windows 2000 Server SP4 and Windows Server 2003 SP2 and later Service Packs, both x86 32-bit, and x64 64-bit.

Might come in handy when you need to get support from Microsoft….

<Recovery>
<powerStateChangeTimeout>120</ powerStateChangeTimeout>
</Recovery>

Like stated above, the time-out value is in seconds. The default value is 120 and it can be changed according to your requirements. This change will be effective when the SRM service has been restarted. (If you can’t find this section in the XML file, just add it…)

logging = true or false
log.rotateSize = maximum size in bytes the file can grow to: 10000
log.keepOld = rotation level, amount of log files to keep: 10
log.fileName = change name and path of log file

1. Disable the pre-logon screensaver:
   Open Regedit
   HKEY_USERS\.DEFAULT\Control Panel\Desktop
   Change the value of “ScreenSaveActive” to 0.
2. Disable updates of the last access time attribute for your NTFS filesystem, especially for i/o intensive vm’s this is a real boost:
   Open CMD
   fsutil behavior set disablelastaccess 1
3. Disable all visual effects:
   Properties on your desktop
   Appearance -> Effects
   Disable all options.
4. Disable mouse pointer shadow:
   Control Panel -> Mouse
   Click on the tab “pointers” and switch “enable pointer shadow” off.

So if you’ve got an addition, please post it and I’ll keep updating this blog post!

• Dominic of VMProfessional created an additional perl script to make storage vmotion a bit easier. It works very simple just edit the script to include your VC url, username, password, cluster and Datacenter, then you will be prompted with a list of VMs to choose from, and a list of target datastore to choose from. Check it out at his website, VMProfessional.
• ASP24 created a PHP website with some easy to use dropdown boxes. It’s hosted on the VMware VMTN forum. I did not had the opportunity to test it by the way.

In my case VMware added the following bit:

cpuid.1.eax = “xxxx————xx————–”
cpuid.1.ecx = “——–R–RR——————-”
cpuid.1.edx = “—————————T—-”
cpuid.80000001.eax.amd = “xxxx————xx————–”
cpuid.80000001.ecx.amd = “—————————-0—”
cpuid.80000001.edx = “——————–H———–”
cpuid.80000001.edx.amd = “—–R————–H——T—-”

This CPU masking surprised me because both Servers are completely the same. Than again ESX 3.5 contains Paravirtualization and Virtualized MMU, and I can image that this functionality is exposed to the VCPU and doesn’t need to be exposed in ESX 3.0.2. Anyone else any thoughts on this?