Yellow Bricks

by Duncan Epping

Howto

Command line tips and tricks #2

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Three totally different command line tips/tricks this time:

  1. Dump a specific disk via the VCB Proxy monolithic(1 big chunk):
    Open a cmd and goto your VCB installation path
    “vcbexport.exe -M 1 -d test01.vmdk -s TestVM/TestVM.vmdk”
  2. Any swapping going on or more info on memory usage in general:
    Open a putty sesion to your ESX box
    “watch -n 1 cat /proc/vmware/sched/mem”
  3. Reinitialize the VirtualCenter Database:
    Stop the service
    Start vpxd.exe with the option “-b”
    CAUTION, this will wipe out the entire database, this is a last resort!

Deleting snapshots when everything else failse…

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The common mis perception of the term “snapshot”, related to VMware, can cause huge problems. I’ve spend a lot of time the last years solving snapshot problems. For once and for all, a snapshot isn’t a static situation like a clone is. A snapshot can best be compared to a redo log, although technically it isn’t because it’s just a bitmap of disk sectors that changed. When you create a snapshot you only create a small “differences” file (*.delta.vmdk) which will contain all the differences until you delete or revert. Please remember reverting(go to) doesn’t delete the differences file! And this file can grow very fast depending on how many changes are made on the disk.

Another thing that people don’t know is the way “delete all” works, but I’ve already outlined that a while ago in a blog.

When you’ve got for instance a 10 levels deep nested snapshot tree with a very large last snapshot it would almost be impossible to press delete all because it will take up a lot of disk space. It would consume a lot of time doing a “delete” for every snapshot, and still it would always take up additional diskspace.

Another way to remove the snapshot is just by cloning the VM to another Datastore. This way you don’t need the extra disk space on the same datastore, and it might be a good moment to consider re-loadbalancing your lun’s again. [Read more…] about Deleting snapshots when everything else failse…

Virtual Machine tweaks for a better performance

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Over the last couple of months I gathered the following tweaks for a better performance insight the virtual machine, besides disabling / uninstalling useless services and devices:

  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!

vscsi stats

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Via the Dutch VMUG site I landed on a new blog, well new… for me new. This blog is maintained by Toni Verbeiren and he created an excellent article about monitoring performance stats for the scsi controllers inside a VM:

A tool is available on ESX 3.5 that creates histograms by default (and complete traces if wanted) is VscsiStats. As an option, one provides the vSCSI handle ID and the VM World ID. In order to get some statistics at all, one first needs to start the monitoring:
./vscsiStats -s

After some time, the relevant statistics can be fetched by issuing a command like:
./vscsiStats -i 8260 -w 1438 -p ioLength

Read more at the source…

There also appears to be a pdf about the subject on the VMware website which contains good information on the subject.

EDIT: You can find the command here: /usr/lib/vmware/bin