Tableau is slow over Azure VPN

Question

Tableau is slow over Azure VPN

reza admin 80

Hello,

Our employees here use Tableau Desktop with our Azure file storage ( Fileshare). When accessing Azure file storage using its public IP address the speed was just fine , but since we have moved Azure file storage to a private link and users are using Azure vpn client, the speed has significantly dropped.

What could be the issue?

FYI, our Azure vpn is in split tunnelling mode.

Thank you

Venkatesan S 4,660 Reputation points Microsoft External Staff Moderator

2026-03-12T18:12:16.58+00:00
Hi reza admin,

Thanks for reaching out in Microsoft Q&A forum,

The main issue boils down to SMB traffic now routing through the slower VPN tunnel and extra network hops instead of zipping directly over the optimized public internet path, and SMB just hates extra latency.

The private endpoint forces all file access (client > VPN > gateway > VNet > storage), adding latency that kills SMB performance Tableau reads tons of small files and metadata, making it extra sensitive. Your split-tunnel setup might also cause inconsistent DNS or routing, where the storage FQDN sometimes hits the public IP instead of private, leading to retransmits. VPN gateway limits and possible MTU fragmentation pile on top.

Check the below steps:

Just run these on a user's machine:

Check raw SMB speed: robocopy \\yourstorage.file.core.windows.net\yourshare C:\temp bigfile.bin /MT:32 (use a 1GB file). If under 10-20 MB/s, VPN or path is the bottleneck.

Ping latency: ping <private IP> (find IP with nslookup yourstorage.file.core.windows.net). Over 50ms? That's your SMB killer.

DNS check: nslookup yourstorage.file.core.windows.net (VPN on vs. off). Must always show private IP when connected.

MTU test: ping <private IP> -f -l 1400 (lower until it passes). Stuck at 1300 or less means fragmentation.

To fix:

Set VPN adapter MTU to 1400 in Device Manager (under Network Adapters > Advanced).

In Azure VPN config, force file.core.windows.net into the tunnel routes check client's route print.

Enable SMB Multichannel on clients (Enable-WindowsOptionalFeature -Online -FeatureName SMBDirect if needed) for better parallelism.

Monitor gateway metrics in portal for saturation during workflows.

If robocopy is slow but pings are fine, it's probably the gateway SKU consider upgrading. For Tableau, local. hyper caching could bridge the gap short-term.

References:

Azure Files networking overview

VPN Gateway FAQ & throughput

SMB performance tuning

Private endpoint config

Kindly let us know if the above helps or you need further assistance on this issue.

Please “up-vote” if the information helped you. This will help us and others in the community as well.
reza admin 80 Reputation points

2026-03-12T18:33:46.95+00:00

Thanks Venkatesan for your response. We are not using any Azure DNS and instead the private ip address and the link have been added to our employee's host files. Is this potentially an issue?

I will do your steps above , except for DNS ones, to see if I can find the bottleneck. Thanks
Venkatesan S 4,660 Reputation points Microsoft External Staff Moderator

2026-03-12T19:12:32.7133333+00:00

reza admin,
No, using hosts files with the private IP for your Azure Files endpoint is not an issue—it's a reliable workaround that ensures consistent resolution to the private IP over VPN, avoiding DNS inconsistencies.