vSphere virtual disk transport modes (VADP) for VM backup

Virtual Disk Transport Methods (VADP) offers interfaces for integration of storage-aware applications, including backup, with efficient access to storage clusters.

Backup vendors may use different transport methods, which provide efficient I/O methods to maximize backup performance and flexible deployment options.

VADP supports four access methods:

• SAN
• SCSI HotAdd
• NBD (network block device) OR NBDSSL
• Local File Access

Network Block Device (NBD)

Description:
NBD allows remote block devices to be accessed over a network as if they were local.

Pros:

• Flexibility: Allows remote storage access.
• Simplicity: Easier to set up than complex storage systems.

Cons:

• Performance: Network latency can slow down data transfer.
• Security: Data is not encrypted, posing a risk on unsecured networks.

Storage Area Network (SAN)

Description:
SAN provides high-speed network access to consolidated block-level storage, typically used in enterprise environments.

Pros:

• High Performance: Low-latency and high-throughput.
• Scalability: Easily add storage devices.
• Reliability: Features like redundancy and failover enhance availability.

Cons:

• Complexity: Requires specialized hardware and expertise.
• Cost: Higher due to infrastructure and management needs.

NBD over SSL (NBDSSL)

Description:
NBDSSL is NBD with SSL encryption, securing data transfer over the network.

Pros:

• Security: Encrypts data in transit, protecting against eavesdropping.
• Flexibility: Maintains the flexibility of NBD with added security.

Cons:

• Performance: Encryption overhead may reduce performance.
• Complexity: Requires SSL certificates and encryption key management.

Local File Access

Description:
Local file access involves reading and writing data on a local storage device, like an internal hard drive or SSD.

Pros:

• Performance: Fastest option with minimal latency.
• Simplicity: Easy to set up and manage.

Cons:

• Scalability: Limited by the physical storage capacity of the local device.
• Flexibility: Not easily shared across machines or networks without additional setup.

Hot-Add Transport Mode

Description:
Hot-add transport mode allows the virtual disk of a VM to be attached to another VM (typically a backup or management VM) while the VM is running, without needing to power down.

Pros:

• Performance: Often faster than NBD, as it avoids network latency by accessing disks directly within the virtual environment.
• Convenience: Can perform data transfers without downtime.
• Integration: Works well in environments where VMs are managed centrally.

Cons:

• Complexity: Requires configuration to enable hot-add capabilities.
• Resource Utilization: Can consume additional resources on the host managing the transfer.

Summary Comparison

• NBD: Suitable for simple, network-based remote storage access with some performance and security limitations.
• SAN: Ideal for high-performance, scalable storage in enterprise setups, but with higher complexity and cost.
• NBDSSL: Adds security to NBD, making it suitable for secure network transfers, with a slight performance trade-off.
• Local File Access: Best for high performance and simplicity in single-machine setups but limited in scalability and network flexibility.
• Hot-Add: Combines performance and convenience for VM environments, allowing for efficient data transfer without downtime, though it requires proper configuration and resource management.

Choosing the right transport mode depends on your specific needs in terms of performance, security, scalability, simplicity, and the nature of your virtualized environment.