Vmware virtual disk types

Vmware supports three different type of disks at this point (5.1)

  • Eager-zeroed thick
  • Lazy-zeroed thick
  • Thin

Eager-zeroed thick:

Disk space is allocated and zeroed out at creation time.   It takes the longest time to create but provides the best possible performance at first use. Mostly used for MSCS and FT virtual machines.

Lazy-zeroed thick

Disk space is allocated but not zeroed at creation time.  The first time your operating system requests a new block it is zero’ed out.   Performance is a little less than Eager-zeroed on first write then equal on each additional write to same sector.


Disk space is allocated and zero’ed upon request.

Which one do you choose?

Well that depends on your needs.  If performance is your critical issue then Thick eager zeroed provisioned is the only choice.  If you need to save disk space or doubt that your customer will really use the 24TB’s of disk space they have requested then thin provisioned is the choice.  Lazy zeroed is something between the two.  At this point vmware recommends Lazy zeroed.

How do I switch?

As of ESXi 5 you have two choices: storage vmotion and inflate.  When initiating a storage vmotion you have the option to choose any of the three options above and convert it.  You can also turn a thin into thick by finding the flat file using the datastore browser and selecting inflate.

SCSI Controller type (Only on first disks):

Much like disk type there are many choices:

  • BusLogic Parallel
  • LSI Logic Parallel
  • LSI Logic SAS – Requires Hardware 7 or later
  • VMware Paravirtual – Requires Hardware 7 or later

Paravirtual is a physical adapter that requires vmtools drivers in order to use.  Paravirtual adapters provide the best performance but can be only used in new operating systems.  Also they cannot be used on boot devices.   Normally your OS selection handles the best scsi type for you.

SCSI Bus Sharing:

When you add a new SCSI Bus you have options on the scsi type but it also gives you the following options (can only be changed when added or vm is powered down)

  • None – Virtual disks cannot be shared
  • Virtual – Virtual disks can be shared between virtual machines on the same server
  • Physical – Virtual disks can be shared between virtual machines on any server

Of course you still need a cluster file system but if you plan on using this system then select Physical.

Scsi bus location:

Each virtual machine can have up to 4 scsi buses each with their own controller.  Lots of people have questioned the advantage of multipe buses in vmware.  In traditional hardware you have multiple buses to provide redundancy in case of a bus failure.  This does not apply to virtual hardware.  But it still provides the virtual operating system multiple channels to handle I/O which is always a good thing.


  • Independent (Not affected by snapshots)
  • Virtual (Default)

Independent Mode:

  • Persistent (Changes are written to disk) – great for databases and other data where a snapshot does not make sense.
  • Nonpersistent (Changes to this disk are discared when you power off or revert to the snapshot) – Used on lab computers, kiosks etc..

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