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VMware updates Timekeeping best practices

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A couple of weeks ago I discovered that VMware updated its timekeeping best practices for Linux virtual machines. December 7th VMware published a new best practice of timekeeping in Windows VMs. (KB1318)
VMware now recommends to use either W32Time or NTP for all virtual machines. This a welcome statement from VMware ending the age old question while designing a Virtual Infrastructure; Do we use VMware tools time sync or do we use W32time? If we use VMware tools, how do we configure the Active Directory controller VMs?
VMware Tools can still be used and still function well enough for most non time sensitive application. VMware tools time sync is excellent in accelerating and catching up time if the time
that is visible to virtual machines (called apparent time) is going slowly, but W32time and NTP can do one thing that VMware tools time sync can’t, that’s slowing down time.
Page 15 of the (older) white paper: Timekeeping in VMware Virtual Machines
http://www.vmware.com/pdf/vmware_timekeeping.pdf explains the issue.

However, at this writing, VMware Tools clock synchronization has a serious limitation: it cannot correct the guest clock if it gets ahead of real time (except in the case of NetWare guest operating systems).

For more info about timekeeping best practices for Windows VMs, please check out KB article 1318 http://kb.vmware.com/kb/1318
It appears that VMware updated the Timekeeping best practices for Linux guests as well.
http://kb.vmware.com/kb/1006427 (9 december 2009)

Impact of mismatch Guest OS type

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During Healthchecks I frequently encounter virtual machines configured with the incorrect Guest OS type specified. Incorrect configuration of Guest OS of the virtual machine can lead to;
• Reduction of performance
• Different default type for the SCSI device *
• Different defaults of devices
• Wrong VMware Tools presented to the Guest OS resulting in failure to install
• Inability to select virtual hardware such as enhanced vmxnet, vmxnet3 or number of vCPUs.
• Inability to activate features such as CPU and Memory Hot Add.
• Inability to activate Fault Tolerance.
• VM burning up 100% of CPU when idling (rare occasions)
Buslogic SCSI Device
* Due to mismatch of Guest OS Type, windows 2000 and Windows 2003 can be configured with a Buslogic SCSI device. Using the Buslogic virtual adapter with Windows 2000 and 2003 will limit the effective IO queue depth of one. This limits disk throughput severely and lead to serious performance degradation. For more information visit KB article 1614
Virtual Machine Monitor and execution mode
Selecting the wrong Guest OS type can be of influence of the selected execution mode.
When a virtual machine is powering on, the VMM inspects the physical CPU’s features and the guest operating system type to determine the set of possible execution modes. This can have a slight impact on performance and in some extreme cases application crashes or BSODs.
VMware published a Must-Read whitepaper about the VMM and execution modes
http://www.vmware.com/files/pdf/software_hardware_tech_x86_virt.pdf
How to solve the mismatch?
vCenter only displays the configured Guest OS of the Virtual Machine, it will not check the installed operating system inside the virtual machine. Powercli offers the solution to this problem, today more and more people start to discover the beauty of Powercli and incorporate this in their day-to-day activities.
So I’ve asked PowerCLI guru Alan Renouf if he could write a PowerCLI script which can detect the Guest OS mismatch.

Get-View -ViewType VirtualMachine | Where { $_.Guest.GuestFullname} | Sort Name |Select-Object Name, @{N=”SelectedOS”;E={$_.Guest.GuestFullName}}, @{N=”InstalledOS”;E={$_.Summary.Config.GuestFullName}} | Out-GridView

Alans “one-liner” checks the configured Gues Os Type in the VM (VM properties) and queries the VMtools to see which operating system it reports.
Once the mismatch is identified, set the correct Guest OS Type in the VM properties as soon as possible. The best way to deal with the mismatch is to power-down the VM before changing the guest OS type.

Upgrading to SRM 4 and SSL certificates

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Recently I started to work on a project implementing SRM 4. One of the project requirements is to use SSL certificates issued by a trusted CA.  When upgrading to SRM 4, we ran into a small problem. Because of a change in the vCenter authentication protocol, a new certificate that complies with the new certificate content rules must be obtained.
The requirements changed of the “Subject Alternative Name”, the SSL certificate issued for SRM 1 environments use the FQDN of the vCenter server host. In SRM 4 environments, the Subject Alternative Name field must contain the FQDN of the SRM server.
This value will be different for each member of the SRM server pair. We installed the SRM server on a separate server, but If you have installed SRM on the vCenter server, then you do not need to acquire a new certificate.

Timekeeping best practices for Linux

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VMware KB article 1006427 presents best practices for Linux timekeeping. These recommendations include specifics on the particular kernel command line options to use for the Linux operating system of interest. There is also a description of the recommended settings and usage for NTP time sync, configuration of VMware Tools time synchronization, and Virtual Hardware Clock configuration, to achieve best timekeeping results.
What surprised me is the recommendation done by VMware; “Note: In all cases use NTP instead of VMware Tools periodic time synchronization”
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006427

Windows 2008 disk alignment

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Due to many performance studies about disk performance it is well known that disk alignment for both VMFS partitions and NTFS file systems improve IO performance such as reduced latency and increased throughput. Alignment of VMFS partitions are done when configuring storage via the VI client but aligning NTFS partitions in Windows system prior to Windows 2008 is a manual task.
Windows Server 2008 use a partition starting offset of 1,048,576 bytes (1,024 KB) for disk larger than 4GB. This provides a well enough alignment for most disks. According to the official documentation, windows 2008 uses a different partition starting offset for disks smaller than 4GB. Or as MS states in the document
Performance Tuning Guidelines for Windows Server 2008
“Note that Windows Server 2008 defaults to a smaller power-of-two offset for small drives.”
But which starting offset does W2K8 exactly use for smaller disks?
[Read more…] about Windows 2008 disk alignment