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walkindakat
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Full Name: Rhian Cohen
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Backing up a VM with multiple disks of different block sizes

Post by walkindakat » Aug 10, 2011 2:24 pm

Hiya

Our DB Admins have created an RHEL 5 (64bit) VM with 9 attached hard disks. These disks are from datastores which have been formatted with different blocksizes as per below

Hard Disk 1 - 1MB
Hard Disk 2- 1MB
Hard Disk 3- 1MB
Hard Disk 4- 1MB
Hard Disk 5- 1MB
Hard Disk 6 - 4MB
Hard Disk 7 - 2MB
Hard Disk 8 - 4MB
Hard Disk 9 - 1MB

We have just encountered 2 errors when snapshotting this machine through just VMware snapshots as per below and from what I can see it is related to the block size and also the high I/O of the server timing out the quiescing. Hopefully the explanations might assist others with similar issues.

I was just wondering if anyone has encountered a similar issue and whether this has stopped Veeam from backing up VM's with this setup? I would test it in Veeam however it is a critical production server so have been asked to get answers before we try another snapshot or Veeam backup operation

"file <unspecified fiename> is larger than the maximum size supported by the datastore '<unspecified datastore>" So far I have found that this error appears to be caused by the VM having disks which are located on datastores which have been created using different block sizes when adding a datastore in VMware. (1MB and 2MB) There isn't a lot you can do here other than have all disks with the same block size attached to a VM. ESXi 4 checks whether the snapshot destination VMFS has a block size equal or greater to the disk you are snapshotting and will fail with the error above if it is too small.

"Can not create quiesced snapshot because the create snapshot operation exceeded the time limit for holding off I/O in the frozen machine."
I have read that this issue occurs because the I/O in the virtual machine is high and the quiescing operation is unable to flush all the data to disk, while further I/O is created. VMware recommend that with busy transactional systems that you should never use a snapshot based backup, you should use agent based backups. (This commonly occurs in SQL/Exchange/Oracle/Citrix)

walkindakat
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Joined: Jun 15, 2011 4:02 pm
Full Name: Rhian Cohen
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Re: Backing up a VM with multiple disks of different block s

Post by walkindakat » Aug 10, 2011 2:44 pm

Found this link which may also help anyone else with similar issues

http://kb.vmware.com/selfservice/micros ... Id=1012384

Gostev
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Re: Backing up a VM with multiple disks of different block s

Post by Gostev » Aug 10, 2011 2:44 pm

Hi Rhian, basically, both explanations above are incorrect. Please search the forum for these errors, as there are many existing topics on both of these issues with correct information. Please feel free to continue posting in the existing topics if needed. Thanks.

Gostev
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Re: Backing up a VM with multiple disks of different block s

Post by Gostev » Aug 10, 2011 3:05 pm

And to save you some time searching, this topic happens to cover both issues above at once ;)

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