Backup & Recovery

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  • 1.  Maximum snapshot size

    Posted Mar 27, 2012 07:13 AM

    Hello,

    I'm currently evaluating the different methods in order to protect one of our virtual machines.  I have a virtualised FileNet server and I want to take snapshots of it. I have tried creating snapshots but I get an 'unspecified error' from the backup software.  A quick search shows that it may be down to the block sizes on the vmware datastore being insufficent, is this correct?  The virtual machine is # 2TB and a file backup takes too long.  The question I suppose is, is there an upper limit for snapshots in vSphere?

    Many Thanks

    Rich



  • 2.  RE: Maximum snapshot size

    Posted Mar 27, 2012 08:32 AM

    Hello,

       i suggest to read this

    http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1012384

    as it explains your issue. And as i understand you can create a snap with a size of the largest possible file that you can create on your vmfs datastore. It's explained in this kb.

    Also please be aware that sometime you can have a vmdk file 256GB where a 256GB max file size is supported. But if you will look on the exact vmdk size it can cave 256.00564something.. and in that case snapshot will fail

    I hope it answers your question.

    Greg



  • 3.  RE: Maximum snapshot size

    Posted Mar 27, 2012 11:40 AM

    Hi,

    I have managed to increase the the size the datastore and the problem still resides.  Upon reading through the documentation is it clear the block size needs to be increased, I will attempt to increase the block size.

    Thanks



  • 4.  RE: Maximum snapshot size

    Posted Mar 27, 2012 06:07 PM
    I will attempt to increase the block size.

    You can't. Switching to another block size would require to recreate/reformat the datastore!

    Since you mentioned the VM is ~2TB in size the issue may be related to the maximum supported disk size in order to be able to create snapshots. In the KB article posted by Grzesiekk you can find a table at the end of the article ("Calculating the overhead required by snapshot files") which lists the maximum disk sizes based on block sizes (btw. for ESXi 5.0 with VMFS-5, only the last line applies)

    Since snapshots are sparse files, the additional space is needed for metadata.

    André



  • 5.  RE: Maximum snapshot size

    Posted Mar 27, 2012 11:45 AM

    wht is the vmfs version you are using? also please check if multiple snapshots are available on the same vm, if yes, commit them and try to take snapshot again