Critical Bug: SQL Server 2025 RC1 on Ubuntu 24.04 – High I/O Wait (~69%) despite official tuning

[micropedro]

Critical Bug Report – SQL Server 2025 RC1 on Ubuntu 24.04

Environment:

• Backup server: Ubuntu 24.04 + SQL Server 2025 RC1
• Production server (control): Ubuntu 22.04 + SQL Server 2022
• Hardware: same host, SSD /dev/sda1 (193GB, 14% usage)
• Kernel: Linux 6.14 (Ubuntu 24.04)

Symptoms:

• Backup server: High I/O wait (~69% average, peaks up to 85.7%)
• Production server: 0% I/O wait under same workload

Optimizations applied (100% official Microsoft Learn recommendations):

• Kernel parameters: vm.swappiness=1, vm.dirty_ratio=80, vm.dirty_background_ratio=3, kernel.numa_balancing=0, vm.max_map_count=1600000
• Transparent Huge Pages: enabled [always], defrag [madvise]
• Disk readahead: 4096 blocks
• I/O scheduler: none
• cgroup v2: CPUQuota=300%, MemoryMax=12GB, MemoryHigh=11GB
• SQL Server: MAXDOP=4, Cost Threshold=50, max server memory=10GB

Results:

• Community checklist: ~58% I/O wait
• Microsoft official tuning: ~69% I/O wait (+11% worse)
• Production (SQL Server 2022): 0% I/O wait

Conclusion:
This is not an OS configuration issue, not SQL Server tuning, and not hardware.
It is a confirmed bug in SQL Server 2025 RC1 when interacting with Ubuntu 24.04 and Linux kernel 6.14 I/O subsystem.
Official Microsoft Learn optimizations make the problem worse.

Request:
Please investigate and patch SQL Server 2025 for Linux compatibility with Ubuntu 24.04 and kernel 6.14. Current release candidate is not production-ready due to critical I/O wait bug.

[tracker1]

This repo is specifically for Dockerized usage... I'd suggest reaching out to MS support directly.

1. https://learn.microsoft.com/en-us/sql/sql-server/sql-server-get-help?view=sql-server-ver17
2. https://support.microsoft.com/en-us/contactus
3. https://support.serviceshub.microsoft.com/supportforbusiness/create