Azure SQL VM Disk Caching Configuration

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 For SQL Server on Azure VMs, the optimal disk host caching choice depends on the disk type and workload:

OS Disk:

  • Read/Write caching - This is the default and recommended setting for OS disks

Data Files:

  • Read-only caching - Best for most SQL Server data files
  • Provides faster read performance while ensuring write operations bypass cache for data consistency
  • Critical for transactional workloads where data integrity is paramount

Log Files:

  • None (no caching) - Always recommended for transaction log files
  • Log writes must be synchronous and durable for ACID compliance
  • Any caching could compromise transaction log integrity and recovery capabilities

TempDB:

  • Read/Write caching - Can be used since TempDB data doesn't need to be durable
  • Helps improve performance for temporary operations

Additional Best Practices:

  • Use Premium SSD (P-series) or Ultra Disk for production SQL Server workloads
  • Enable Write Accelerator for log files on M-series VMs if using Premium SSD
  • Consider disk striping for larger databases to improve IOPS and throughput
  • Place data and log files on separate disks for optimal performance

The key principle is balancing performance with data consistency requirements. Log files require the strictest durability guarantees, while data files can benefit from read caching without compromising integrity.

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