Recover XenServer VHD Volumes

So you blew up your CloudStack installation and all you have is a chain of XenServer VHD files on your primary storage.

The recovery process would involve creating a coalesced volume from the available VHD chain files. The steps outlined in CloudStack’s CreateVolumeFromSnapshotCommand API says…

* Given the UUID of a backed up snapshot VHD file on the secondary storage, the execute of this command does
* 1) Get the parent chain of this VHD all the way up to the root, say VHDList
* 2) Copy all the files in the VHDlist to some temp location
* 3) Coalesce all the VHDs to one VHD which contains all the data of the volume. This invokes the DeletePreviousBackupCommand for each VHD
* 4) Rename the UUID of this VHD
* 5) Move this VHD to primary storage

Comment numbered (1), (2) and (3) are what we are interested in. So using vhd-util, you can coalesce the chain VHDs as below:

# vhd-util scan -f -m'*.vhd' -p
vhd=c15d6628-0109-4e7a-9b45-28ed4e2fbbed.vhd capacity=21474836480 size=1155727872 hidden=1 parent=none
   vhd=c32d7e83-6c1e-4609-8ff3-a44ff50e1af3.vhd capacity=21474836480 size=1529294848 hidden=0 parent=c15d6628-0109-4e7a-9b45-28ed4e2fbbed.vhd
# vhd-util coalesce -n c32d7e83-6c1e-4609-8ff3-a44ff50e1af3.vhd 

This would be a manual step for each VHD chain you have. Once the VHD is coalesced, import the parent as a regular XenServer VHD template and manually set the OS Type. Some trial and error might be required to get the OS type right.

Finally, launch a new instance from the imported template.

References

OpenStack – XenServer – type Image to Volume (Citrix Blog)

Shanker Balan

Shanker Balan is a devops and infrastructure freelancer with over 14 years of industry experience in large scale Internet systems. He is available for both short term and long term projects on contract. Please use the Contact Form for any enquiry.

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