Azure App Service Linux CIFS filesystem extremely slow causing 20–35 second WordPress/WooCommerce response times

We migrated a production WooCommerce/WordPress site from SiteGround to Azure App Service Linux.

The application experiences extremely high server-side response times (TTFB between 10 and 35 seconds).

We have completed extensive troubleshooting and isolated the issue away from the application itself.

The application was tested on both Basic B3 and Standard S2 App Service Plans with no meaningful improvement in response time.

Environment

• Azure App Service Linux

• PHP 8.2

• Azure Database for MySQL Flexible Server

• WooCommerce

• Divi Theme

• App Service Plan tested on both B3 and S2

Completed investigations

✓ Database queries are not the bottleneck (approximately 0.5 seconds using Query Monitor)

✓ PHP bootstrap profiling shows more than 8 seconds spent before page rendering

✓ OPcache tuned (memory, interned strings, max accelerated files)

✓ Heavy plugins disabled individually

✓ App Service scaled from B3 to S2

✓ No significant performance improvement after scaling

Filesystem investigation

Application storage is mounted as:

/home

Type: CIFS (SMB)

Verified using:

mount

Benchmark results

Local filesystem

time find /tmp -maxdepth 2

Result:

0.019 seconds

Application filesystem

time find /home/site/wwwroot/wp-content/plugins -type f

Result:

14.96 seconds

The application contains approximately 13,500 PHP files.

This demonstrates extremely high filesystem metadata latency.

Observed page response times

Home:

10–18 seconds

Product:

10–17 seconds

Cart:

10–16 seconds

Checkout:

20–37 seconds

Evidence

Filesystem

Filesystem Type:

SMB2

Filesystem benchmark

Local disk:

/tmp

0.003 seconds

Application storage:

/home/site/wwwroot/wp-content/plugins

14.302 seconds

HTTP benchmark

Checkout page

TTFB: 24.005 seconds

Total: 24.065 seconds

Database

Query Monitor reports database execution around 0.5 seconds.

Questions

1. Is this level of SMB2 filesystem latency expected on Azure App Service Linux?
2. Can Microsoft confirm whether the application content share is causing this metadata latency?
3. Is Microsoft recommending Custom Containers or Run From Package for large WordPress/WooCommerce applications with many PHP files?
4. Is there any supported way to keep application code on local SSD instead of the mounted SMB share while remaining on Azure App Service?