In this continuing series of blog posts we are going to cut through the self-serving and competing claims and examine each of the arguments in favor and against the various techniques used for virtual data protection. You can check out the first post from this series here. Today’s post will discuss virtualizaton backup approaches.

Picking up where we left off last week, we’re going to explore the primary advantages and disadvantages of GOS-level protection versus HOS-level protection. Today we will conclude our discussion, but if we’ve missed a feature that you would like to see discussed, please leave us a comment.

Microsoft Hyper-V CSV (Cluster Shared Volume) Support

A CSV is a volume that is simultaneously available to directly read from and write to by all notes of a Microsoft failover cluster.  CSVs enable an IT administrator to reroute data over the network in the event that a node loses its path(s) to the shared storage array.

HOS-level protection typically works with virtualization constructs such as CSV.  GOS-level protection is implemented at a level lower than the virtualization infrastructure and thus depending upon implementation will not support virtualization constructs such as CSV. This is the case for one major vendor who released and then had to de-release CSV support (AppAssure.)  Note that in “theory” GOS-level protection could support CSV; in practice it’s proven a bit difficult for some vendors.

Advantage: HOS-level protection

VMware vCenter and VMware HA Support

VMware vCenter Server provides centralized management of vSphere virtual infrastructure.  vCenter is an aggregation mechanism that allows IT administrators to gain centralized control and visibility into their vSphere deployment, provide proactive management, and manage multiple vCenter Server instances.

Data protection products that operate at the HOS-level are able to work directly with VMware vCenter and handle situations such as a virtual machine migrating from one ESX/ESXi host to another.

HOS-level protection typically works with virtualization constructs such as VMware vCenter Server.  GOS-level protection is implemented at a level lower than the virtualization infrastructure and thus don’t typically support virtualization constructs such as VMware vCenter Server.  Note however that GOS-level protection will work with other virtualization constructs, such as vMotion, that are implemented “underneath” the GOS such that GOS-level protection does not have to be aware of their existence.

Advantage: HOS-level protection

VMware Free (Unlicensed) ESXi Support

As noted previously, VMware free (unlicensed) ESXi doesn’t support the use of VADP – thus HOS-level protection is not possible.  GOS-level protection, where each virtual machine is treated as a physical machine, is the only option possible.

Advantage: GOS-level protection.

VMware RDM (Raw Device Mapping) in Physical Compatibility Mode

VMware’s VADP doesn’t support VMware RDM in physical compatibility mode.  Thus GOS-level protection must be used to protect this particular configuration.  Note that GOS-level protection that is block-based will not work in this situation; only a more flexible approach will work.

Advantage: GOS-level protection (if not implemented as block-level backup)


There’s only one easy answer in terms of virtualization data protection – and that’s to reject dogma and embrace facts in order to find the optimal data protection solution for your unique IT infrastructure.  Vendors shouldn’t ask you to conform to their data protection offerings; instead they should prove to you how their solution can flexibly adapt to your existing IT infrastructure as well as enabling you to respond to future needs and requirements of your business and your users in an agile manner.

What do you think?