Quest vRanger and Direct-To-Target Backups
Direct-To-Target backups can generally significantly increase parallelism and backup performance. In the vRanger architecture, each ESX host would be the “data mover” and collect the bits and write them directly to the backup target (CIFS or NFS). Quest has noted that customers have experienced significant performance improvements with Direct-to-Target over proxy architectures where the “data mover” can become a bottleneck.
ESXi however created a problem for this Direct-to-Target capability. With ESXi being a bare-metal hypervisor, it was no longer possible to inject run-time binaries onto the ESX host. Thus when ESXi is used, all the backup traffic is now passing through the vRanger server itself – acting as a backup proxy. This is why some have noticed a drop in backup performance after deploying ESXi in a vRanger environment.
What can be done for ESXi hosts? For the moment, all you can do is use either fiber-based (LAN free) backups and/or leverage ESX’s CBT (Changed Block Tracking) to reduce backup times.
But in order for true Direct-To-Target capability with ESXi, vRanger customers will have to wait until next quarter (Q1 2011) when a VA (virtual appliance) architecture will be introduced. In this design, an appliance VM will run from each ESXi host and use the hot-add capability of the vStorage API to mount each VMDK as read-only and perform the backup operation.
Quest has a detailed whitepaper on this VA solution, and an illustration is provided below.