image When it comes to architecting jobs for VMware vSphere virtual machines, the Automatic option for the Transport mode proxy configuration is the best option if you are not giving too much thought to the configuration. The Automatic option goes through a number of communications options checks to see what’s available on the proxy and determine the best way to back up the VM. This decision process has a number of factors that go into the mode selection for the active job. Direct SAN access is favored first in all situations, virtual appliance hot-add as the next best thing, and Network Mode as the common denominator to work in most every situation to sum up the process.

Transport mode is a property of each proxy (with version 6 of Veeam Backup & Replication), as shown below:

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During a recent convergence of Veeam technical staff members, three situations were listed when Network Mode may be the best choice for a proxy and its associated job(s), including:

1. VM change-rate awareness. If you happen to be in tune with the change rate behavior of your VMs, taking a look at that behavior will help you determine how much change has incurred. For example, a system that simply takes on new log messages for the day and does not run a database may have a very low change rate. This low change rate may be best suited for Network mode, which would omit the API steps required to hot-add, and subsequently hot-remove the virtual disk(s) to an additional VM.

2. Direct SAN mode is not available. In all situations, although this mode is the best, it isn't always available for all environments. With NFS-based storage systems, for instance, it may be best to save the step of checking for Direct SAN mode availability in favor of Network mode. The per-job and per-iteration check can be omitted by explicitly selecting Network Mode.

3. A large amount of VMs per job. There are a lot of good reasons to have a large number of VMs per job, such as to increase deduplication within that backup job. Virtual appliance hot-add requires a few steps to be run within the job from the proxy that are repeated for each VM. These steps, multiplied across a number of VMs can add time to the overall job. Couple this with the low change rate that may occur, and the overall proxy efficiency can increase. You may see the “reconfigure virtual machine” event occur on both the VM being backed up as well as the proxy VM. Below is a proxy which has a series of these events occur during a backup job using virtual appliance hot-add:
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As a general rule, the Automatic option is the best selection to make. However, awareness of your environment and the ability to access the "knobs and dials" will allow more granular configuration options that in some situations—even with Network mode—allow you to run quicker vSphere backups.

Have you ever explicitly chosen Network mode for a proxy configuration? If so, what were some of the factors that influenced you? Share your comments below.

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    • bhwong

      Direct SAN access is dangerous as we don’t want Windows to write NTFS into VMFS storage. Not all SAN storage allow us to configure read-only for Windows iSCSI to prevent this potential danger from occurring.

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    • Daniel Manthey

      I have one job with several VMs. I try to improve the job preformance, because one machine (500GB) falls back from CBT to HOT-ADD, and I can’t figure out why. So I’ll try this. Any suggestoins what else causes the machine to use HOT-ADD instead of CBT?

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      • Rick Vanover

        Network mode vs. hot-add is one thing, usually determined by the proxy configuration. CBT not being available is usually a permission of the VM itself. One question is if this VM is occasionally a Veeam VMware Backup Proxy – that disables CBT on it.

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    Rick Vanover
    Author: Rick Vanover
    Rick Vanover (MVP, vExpert, Cisco Champion) is the director of Technical Product Marketing & Evangelism for Veeam Software based in Columbus, Ohio. Rick’s IT experience includes system administration and IT management; with virtualization being the central theme of his career recently.
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    Published: January 12, 2012