Comparing ExpressRoute vs Site-to-Site VPN for large-scale backup operations

Cloud Platforms Microsoft Azure
, , , , , , , ,
1

We’re evaluating network connectivity options for our hybrid backup strategy where on-premises data (15-20TB monthly) needs to flow to Azure Storage. Currently considering ExpressRoute versus Site-to-Site VPN, and I’d like to hear from folks who’ve implemented either for backup workloads.

Our backup windows are tight (6-8 hours nightly), and we’re concerned about throughput consistency and cost implications. The VPN option is obviously cheaper upfront, but I’m wondering about real-world bandwidth limitations and reliability for sustained large transfers. ExpressRoute provides dedicated bandwidth but comes with significant monthly costs.

What have been your experiences with backup performance over these connection types? Are there hidden costs or limitations we should consider? Also curious about hybrid strategies - some companies seem to use VPN for control plane and ExpressRoute for data plane.

2

For hybrid routing, we use BGP communities to control route advertisement. ExpressRoute advertises more specific routes for Azure Storage service tags, while VPN advertises broader Azure address spaces. On-premises, we use policy-based routing to direct traffic based on destination. The backup servers have routes pointing to ExpressRoute gateway for storage endpoints, while management tools route through VPN. This requires careful planning because Azure VNet can only have one default route. We also implement QoS policies on both connections - backup traffic gets lower priority during business hours on ExpressRoute to preserve bandwidth for production workloads.

3

One aspect often overlooked: backup software behavior over these connections. Some backup solutions don’t handle high-latency links well, and VPN adds 20-50ms latency versus ExpressRoute’s 5-15ms for most regions. We tested Veeam and CommVault over both - CommVault’s deduplication worked better over ExpressRoute due to lower latency for metadata operations. Also consider that VPN throughput degrades with packet loss, while ExpressRoute’s private connection is more resilient. For large-scale backups, you want consistent throughput, not peak throughput. We calculated our TCO over 3 years and ExpressRoute was only 15% more expensive when factoring in reduced backup window SLA violations.

4

Don’t forget about ExpressRoute Direct as an option if you’re moving serious data volumes. Standard ExpressRoute goes through provider networks with some oversubscription, but Direct gives you 10 or 100 Gbps ports directly to Microsoft. For 20TB monthly, you probably don’t need it, but if your backup volumes grow, it becomes cost-effective around 50TB monthly. Another consideration: ExpressRoute supports FastPath which bypasses the VNet gateway for data plane traffic, reducing latency further. We saw 30% improvement in backup throughput after enabling FastPath. The downside is complexity - you need network engineers who understand BGP and routing policies deeply.

5

Cost structure is critical to understand. ExpressRoute isn’t just the circuit cost - you pay for outbound data transfer, the ExpressRoute gateway in Azure, and your provider’s port fees. For 20TB monthly, you’re looking at $1,500-2,000 in data egress alone on top of circuit costs. VPN costs are primarily the VPN Gateway SKU (VpnGw3 for 1.25 Gbps is around $350/month) plus minimal data transfer fees. However, VPN bandwidth is shared and best-effort. If your backup window tolerance is strict, ExpressRoute’s SLA (99.95%) versus VPN’s gateway SLA (99.95% but no bandwidth guarantee) matters. We use a hybrid approach: VPN for management traffic and small backups, ExpressRoute for production database dumps.

6

We migrated from Site-to-Site VPN to ExpressRoute specifically for backup traffic. The VPN was theoretically capable of 1.25 Gbps but in practice we saw 600-800 Mbps with significant jitter during peak hours. The overhead from IPsec encryption also consumed CPU cycles on our VPN gateway. ExpressRoute gave us consistent 2 Gbps with sub-10ms latency. For 15-20TB monthly, you’re looking at roughly 55-75 Mbps average sustained throughput, which VPN could handle, but backup windows need burst capacity. ExpressRoute’s predictable performance was worth the cost for us - we reduced backup windows by 40%.

7

After reading through everyone’s experiences, here’s my synthesis on the ExpressRoute vs VPN decision for backup workloads:

Bandwidth and Performance Characteristics: ExpressRoute provides dedicated, predictable bandwidth with consistent throughput. In production environments handling 15-20TB monthly, this translates to reliable 6-8 hour backup windows. VPN offers theoretical bandwidth (up to 1.25 Gbps on VpnGw3) but real-world performance typically achieves 60-70% of maximum due to IPsec overhead and internet path variability. The key difference: ExpressRoute delivers consistent performance while VPN is best-effort.

Cost Structure and TCO Analysis: VPN appears cheaper initially ($300-400/month for gateway) but lacks bandwidth guarantees. ExpressRoute costs break down as: circuit fee ($500-3,000/month depending on bandwidth), ExpressRoute gateway ($200-600/month), and data egress ($0.025-0.087/GB). For 20TB monthly, total ExpressRoute cost runs $2,500-4,000/month versus $400-600 for VPN. However, factor in soft costs: missed backup windows, potential data loss from failed transfers, and staff time troubleshooting performance issues. Our 3-year TCO analysis showed ExpressRoute only 15-20% more expensive when including operational costs.

Hybrid Network Strategies: The most sophisticated implementations use both technologies strategically. Common patterns:

  1. Control/Data Plane Split: VPN for management, monitoring, and small transfers; ExpressRoute for bulk data movement
  2. Active/Backup: ExpressRoute primary with VPN failover (requires careful BGP tuning)
  3. Tiered Approach: ExpressRoute for production backups, VPN for test/dev environments

Implementing hybrid requires BGP expertise for route manipulation, policy-based routing on-premises, and potentially Azure Route Server for complex topologies. Use BGP communities to control route advertisement and AS-path prepending for failover scenarios.

Decision Framework: Choose VPN if: backup windows are flexible (12+ hours), monthly data volume < 10TB, budget is primary constraint, or you’re in testing phase.

Choose ExpressRoute if: strict backup SLAs, monthly volume > 15TB, low latency required for backup software (dedup, metadata), or you need predictable performance for compliance.

Recommendation for Your Scenario: With 15-20TB monthly and 6-8 hour windows, you’re borderline. I’d start with VpnGw3 (1.25 Gbps) and monitor actual throughput for 30 days. If you consistently achieve > 900 Mbps and meet backup windows, VPN suffices. If you see degradation or window violations, the business case for ExpressRoute becomes clear. Many organizations start with VPN and migrate to ExpressRoute as data volumes grow - this staged approach reduces upfront investment while providing upgrade path.

8

These are excellent points. The latency impact on backup software is something I hadn’t fully considered. Our backup solution does heavy metadata operations during synthetic full backups. Regarding the hybrid approach mentioned - how do you handle routing policies to ensure backup traffic goes over ExpressRoute while keeping management traffic on VPN? Is this done through BGP route preferences or application-level configuration?