Introduction
Since vSphere 5.1, VMware offers an easy migration path for VMs running on hosts managed by a vCenter. Using Enhanced vMotion available in Web Client, VMs can be migrated between hosts, even if they don’t have shared datastores. In vSphere 6.0 cross vCenter vMotion(xVC-vMotion) was introduced, which no longer requires you to even have old and new hosts be managed by the same vCenter.
But what if you don’t have a vCenter and you need to move VMs between standalone ESXi hosts? There are many tools that can do that. You can use V2V conversion in VMware Converter or replication feature of the free version of Veeam Backup and Replication. But probably the easiest tool to use is OVF Tool.
Tool Overview
OVF Tool has been around since Open Virtualization Format (OVF) was originally published in 2008. It’s constantly being updated and the latest version 4.2.0 supports vSphere up to version 6.5. The only downside of the tool is it can export only shut down VMs. It’s may cause problems for big VMs that take long time to export, but for small VMs the tool is priceless.
Installation
OVF Tool is a CLI tool that is distributed as an MSI installer and can be downloaded from VMware web site. One important thing to remember is that when you’re migrating VMs, OVF Tool is in the data path. So make sure you install the tool as close to the workload as possible, to guarantee the best throughput possible.
Usage Examples
After the tool is installed, open Windows command line and change into the tool installation directory. Below are three examples of the most common use cases: export, import and migration.
Exporting VM as an OVF image:
> ovftool “vi://username:password@source_host/vm_name” “vm_name.ovf”
Importing VM from an OVF image:
> ovftool -ds=”destination_datastore” “vm_name.ovf” “vi://username:password@destination_host”
Migrating VM between ESXi hosts:
> ovftool -ds=”destination_datastore” “vi://username:password@source_host/vm_name” “vi://username:password@destination_host”
When you are migrating, machine the tool is running on is still used as a proxy between two hosts, the only difference is you are not saving the OVF image to disk and don’t need disk space available on the proxy.
This is what it looks like in vSphere and HTML5 clients’ task lists:
Observations
When planning migrations using OVF Tool, throughput is an important consideration, because migration requires downtime.
OVF Tool is quite efficient in how it does export/import. Even for thick provisioned disks it reads only the consumed portion of the .vmdk. On top of that, generated OVF package is compressed.
Due to compression, OVF Tool is typically bound by the speed of ESXi host’s CPU. In the screenshot below you can see how export process takes 1 out of 2 CPU cores (compression is singe-threaded).
While testing on a 2 core Intel i5, I was getting 25MB/s read rate from disk and an average export throughput of 15MB/s, which is roughly equal to 1.6:1 compression ratio.
For a VM with a 100GB disk, that has 20GB of space consumed, this will take 20*1024/25 = 819 seconds or about 14 minutes, which is not bad if you ask me. On a Xeon CPU I expect throughput to be even higher.
Caveats
There are a few issues that you can potentially run into that are well-known, but I think are still worth mentioning here.
Special characters in URIs (string starting with vi://) must be escaped. Use % followed by the character HEX code. You can find character HEX codes here: http://www.techdictionary.com/ascii.html.
For example use “vi://root:P%40ssword@10.0.1.10”, instead of “vi://root:P@ssword@10.0.1.10” or you can get confusing errors similar to this:
Error: Could not lookup host: root
Disconnect ISO images from VMs before migrating them or you will get the following error:
Error: A general system error occurred: vim.fault.FileNotFound
Conclusion
OVF Tool requires downtime when exporting, importing or migrating VMs, which can be a deal-breaker for large scale migrations. When downtime is not a concern or for VMs that are small enough for the outage to be minimal, from now on OVF Tool will be my migration tool of choice.
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