Migrating images
Migrating VMs from one server host to another happens for a variety of reasons, ranging from load balancing to application aggregation.
Migrations for our direct comparisons here revolve around taking snapshots of existing working VM guests and then moving these images to new target server hypervisor hosts.
VMware offers an optional live migration tool available call VMotion. Our prior experience with ESX VMotion is that it can move images within seconds from one server hypervisor to another. Microsoft recently announced a similar server for Hyper-V won’t be available until 2010, a serious deficiency were we to include this in our direct comparison.
By using snapshots under Hyper-V, we were able to capture live system state data on either Windows 2008 or Novell’s SUSE Linux Enterprise Server 10.2 VMs.
A loaded machine took seconds for the snapshot to complete. The snapshot feature can be used to roll-back or restore a server's use state, but there are implications. For example, as transactional states of applications are frozen, the server becomes unavailable for a short period of time, and so users may find their applications performing badly because they cannot access the server while the snapshot state is being taken. Further, the snapshot of a system state, where the image rendered is then used subsequently as an instance on another machine, may or may not be supported in operating system and/or application licensing. Microsoft recently changed its policy to allow VM instances to be migrated (for various versions of Windows) from one host to another, but licensing prohibits spontaneous movements of VM instances, whatever their state. That state may also represent application or file states that when re-instantiated, require maintenance. Transaction states may also have to be verified as well.
VMware's Virtualized Consolidated Backup (VCB) that’s included in the VMware Infrastructure Foundation edition that we tested, adds full and incremental backup to disk or tape of guest hosts. The file system is quieted during backup to keep things synchronized, possibly, and temporarily, removing VM guest operating system/applications from availability through the process. VMware says VCB also has integration capability with CommVault EMC, HP, Symantec, IBM/Tivoli, and other backup applications, but we did not test that level of integration.
VMware's ESX uses one of two capture systems to pull VM images, one that develops a VM image from a live, running server, or one that takes a shutdown-server’s disk and captures the state of the disk. We captured several operating systems and found that this is a simple process that works well and consistently.