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Can not create snapshot for 1TB VM Guest on ESXi 4 Host

  • 1.  Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 07, 2012 12:32 AM

    I have an ESXi 4.1 host with local storage.  I am trying to use a third party backup product called PHD that uses snapshots to backup VMs.  I have a 1TB VM that is on a local storage data  store that only has about 190GB free.   I am receiving an error that a snap shot can not be created due to space.

    My question is this, is there away around this?  I have another local data store on that host that has about 500GB free.  Is it possible to use that other data store for this VM's snapshots?

    Any helpd would be greatly appreciated.

    Thanks in advance,

    Dave



  • 2.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 07, 2012 04:59 AM

    PHD is just being cautious with its default settings. VMFS will let you take a snapshots until your datastore is completely full, so a lot of backup products will default to a "safe" setting around 20% to avoid that situation. You should determine what's appropriate for your environment though.

    See this PHD post for details. You can lower the "Available free space before aborting backups" setting to something you're comfortable with. Try 100 GB and see if you're successful.

    Essentially what happens when you take a snapshot is that your existing VMDK flat file is locked read-only, and changed blocks get written to a delta VMDK file. That snapshot delta file has the potential to grow up to the entire size of the original virtual disk, if you touch every single block before the snapshot is deleted (i.e. committed). If you don't write anything to the virtual disk during this time, the space consumed by just having a snapshot present is negligible.

    Hope that helps. If you're looking for a quick crash-course on VMFS snapshots, Ruben Garcia has an excellent writeup on them here.



  • 3.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 07, 2012 05:42 AM

    Hi,

    I think it might be the space issue , Kindly check for the space requirment with the help of the below formula.

    (Size  of virtual machine's hard disk(s)) + (size of RAM for virtual machine) + (100MB  for log files per virtual machine)

    OR

    For more details go the below link

    http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003755



  • 4.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 07, 2012 08:14 PM

    Unless the setting mentioned by AndySimmons solves your issue, try to create a snapshot manually to see whether this works. If it does not work, you are most likely running the VM on a datastore with a 4MB block size and the virtual disk is larger than 1016GB.

    For details see "Calculating the overhead required by snapshot files" at http://kb.vmware.com/kb/1012384

    André



  • 5.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 07, 2012 11:26 PM

    It is a 4MB block. I haven't tried to manually create a snapshot yet. Is there anything that can be done if it is a 4MB block?



  • 6.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 07, 2012 11:36 PM

    Unfortunately the block size cannot be changed without reformatting the datastore. Your options are either to evacuate the datastore and recreate it with an 8MB block size (backup and restore the VMs) or migrate the VM to another datatore with an 8MB block size. Another alternative - depending on your environment - is to upgrade the host to ESXi 5.0 which allows to upgrade the datastore to VMFS-5. VMFS-5 will then allow virtual disks with up to 2TB minus 512 bytes.

    André



  • 7.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 11, 2012 03:47 PM

    Is it possible to use another datastore for the snapshots and configure that datastore with 8MB block size?



  • 8.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 11, 2012 03:58 PM

    You could create a new datastore with the 8MB block size, and storage vMotion the 1 TB disk off to that other datastore.



  • 9.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 11, 2012 03:58 PM

    Also currently the VMDK is setup to 1024.  Is it possible to reduce the size of this drive?  The guest O/S is Server 2008.



  • 10.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 11, 2012 04:01 PM

    EDIT: Cutting this post to avoid confusion. See Andre's post below.



  • 11.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 11, 2012 04:08 PM

    You cannot shrink a virtual disk that easy. You'd have to use e.g. VMware Converter for this.

    Regarding the snapshot location, you could specify the "workingDir" in the VM's settings to create the snasphots on another datastore (see http://kb.vmware.com/kb/1002929)

    André

    @AndySimmons

    It makes no difference whether the virtual disks are provisioned thin or thick. What counts is the provisioned disk size, as this will be the maximum disk size (plus some overhaed) to which a snapshot could grow.



  • 12.  RE: Can not create snapshot for 1TB VM Guest on ESXi 4 Host

    Posted Feb 15, 2012 05:36 AM

    Setting 'WorkingDir' works from the VMware side for a different snapshot location but I don't believe PHD supports that. You may want to double check with their support on that question.

    Pete

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