Storage vMotion was introduced with ESX 3.5 about a year ago but for various reasons I’ve never had the opportunity or need to use it until now. The project that required its use has been knocking around for a few months now. It started as a single ESX server that was to be used to build a small number of VMs for use by my customer as an HR system. Three months or so after putting in that first host I was finally called back to add another and setup VirtualCenter. Installing ESX, VC and doing all of the necessary configuration was straightforward (mostly), I’ve done it a number of times before. Migrating the live VMs from their location on local storage on the first host to a SAN LUN was the new bit, the bit that required Storage vMotion. It didn’t go smoothly all the way.
vMotion (the movment of a running VM from one host to another without downtime) is an established technology. It works and it’s built into the VI client. Storage vMotion functionality doesn’t have a button or context menu entry for it by default. It needs to be invoked from a command line or a plugin needs to be installed. I investigated two options, tried them both and still had a few issues.
Simple SVMotion GUI by Alexander Gaiswinkler
In the hunt for svmotion utilities, this is the one that I found first. It can be downloaded from a link in a VMware communities thread here and requires the Remote CLI for VMware to be installed. Installation of the SVMotion GUI isn’t too difficult. It is merely a zip file containing a perl script and a Windows executable. The perl script has to be moved to the bin directory of the Remote CLI installation. The executable can be placed anywhere and just exeuted to launch the GUI.
The GUI is quite straightforward to use although there are a couple of problems that I encountered. The first was with the datacenter name. VirtualCenter will allow you to create a datacenter with a name that contains certain characters that the Simple SVMotion GUI will not work with. Spaces for instance. The datacenter name had been selected as “xxx – London”. The GUI was unable to connect and return a list of datastores when this was entered so I had to rename the datacenter in VirtualCenter to be just “xxx”.
The second issue I hit was with the source datastores. When ESX was installed a VMFS partition was created automatically with the remainder of the disk space after all of the other partitions had been sized. ESX creates this datastore with a name of “[hostname:storage1]” or something like that. The colon caused a problem with the svmotion.pl script however so I had to rename the datastore to “[hostname_storage1]”.
With those two issues sorted I was able to svMotion two of the five VMs stored locally on one host to the SAN space. The other three would not go but that’s a story for later.
Simple SVMotion GUI is certainly simple but it does it’s job. There are limitations though.
vip-svmotion by Andrew Kutz
This is actually a plugin for the VI client and looks a lot like what you would expect VMware to create themselves. Who knows, the next release of VirtualCenter and the VI client may include it. The plugin can be downloaded from SourceForge here and the installation is straightforward. In fact, once installed, the plugin is automatically enabled within the VI client.
Using it is pretty simple, just right click on a VM and select Migrate Storage… from the context menu.
This opens a window that shows the currently configured storage and allows a new location to be selected. My apologies, I would included a screenshot with lots of detail but I have to be careful about pasting customer specific data into a public blog!
The top for disk icons are the local storage on the two hosts. The VM (and its single Hard Disk) is stored on the second local VMFS of the first host. Relocating the storage is simply a case of dragging the VM (the grey box) to the SAN LUN (the bottom disk icon) and applying the change.
This is more like how svMotion should be done. It’s all kept in the VI client and is easy to follow.
Other svMotion Issues
I mentioned that I had some other issues with svMotion. Three of the VMs that I had to move would not go. In case anyone else runs into these problems, I will describe them here.
1. Floppy drive
A handful of the VMs had actually been migrated from an old ESX 2.x environment and the default hardware configuration had probably not been changed when they were first setup. The new ESX hosts (HP DL585s) did not have floppy drives fitted yet the .vmx file for two of the VMs were trying to map virtual floppy drives to a real one on the host. For some reason this was causing the following message to appear when svMotion was attempted:Device ‘Floppy Drive 1’ has a backing type that is not supported. This is a general limitation of the host.
VirtualCenter won’t let me remove the floppy drive while the VM is running and it also suggested that the .vmx file had been edited by hand at some point. So, to fix this I’m going to have to shut down the VM which is unfortunate as that was the whole point of using svMotion in the first place.
Once I got change approval to shut the VM down, I downloaded the .vmx file and changed the floppy configuration to remove the floppy drive.floppy0.present = “true”
becamefloppy0.present = “false”
The VM had to be removed from inventory and then re-added with the modified .vmx file but after that Storage vMotion worked fine and the VM booted without issue.
2. Independent Disks
Again I believe that this is a VM from an older 2.x host. This time the hard disk is set to be in independent-persistent mode. I will have to shut down the VM and change the setting to allow svMotion to work. The error message that VMware provides is pretty clear as to what the problem is:
A general system error occurred: The virtual machine has virtual disk in indepedent-persistent mode that prevents migration.
Michael is a Senior Consultant for Xtravirt. If it's got buttons or flashy lights on it then it'll probably be on his radar. When not "mending computers" (it's sometimes easier than explaining "cloud" to relatives), Michael provides essential education, entertainment and trampoline services to his two children.