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Checking the alignment status of virtual machines

Check the alignment status of a virtual machine to determine whether it is aligned or misaligned. You should fix the alignment of a misaligned virtual machine to optimize I/O performance.

Before you begin

You should have scanned your datastores.


  1. In the Optimization and Migration page, select a datastore from the datastores table (the table at the top of the page).
    Screen shot: The datastores table showing a selected datastore.
    After you select a datastore, the virtual machines running on that datastore appear in the virtual machines table (the table at the bottom of the Optimization and Migration page).
  2. In the virtual machines table, view the Alignment State column to identify the alignment state of the virtual machines on that datastore.
    Tip: To quickly identify any misaligned virtual machines, select Show only misaligned virtual machines.
    Note: The View Disk Details button shows you the alignment details of a virtual machine's VMDKs.
    Screen shot: The virtual machines table showing a virtual machine with the status Misaligned, Online migration capable.
    The following states can appear in the Alignment State column:
    For this state... Do this...
    Actually aligned Nothing.

    The partitions of the virtual machine's hard disk are aligned to the storage system and start at the correct offset.

    Functionally aligned Nothing.

    The partitions of the virtual machine's hard disk are misaligned; however, when residing on an optimized datastore, they align on correct boundaries. As a result, the virtual machine performs as though it is aligned.

    If you want to clone a functionally aligned virtual machine, you should take it offline and fix the VMDK alignment before you clone it. Otherwise, the clones can be misaligned if the destination datastores are not optimized for the VMDK layout of the clones.

    Misaligned, Offline alignment only Power down the virtual machine and align the VMDK using a tool such as VMware vCenter Converter.

    The virtual machine is misaligned; however, VSC cannot align it due to either of the following:

    • The virtual machine has more than one disk with different offsets
    • The virtual machine has multiple disks spanning multiple datastores
    Misaligned, Online migration capable Use VSC to perform an online alignment.
    Other Review the following reasons why VSC cannot determine the alignment state of the virtual machine:
    • It is inaccessible or reports an error during read attempts
    • It has a disk size of 0
    • It does not have any partitions
    • It has independent disks or dynamic disks
  3. Repeat steps 1 and 2 for each datastore.