4.1.1.3. Configure VM Storage

💡 First Principle: Selecting the appropriate managed disk type and configuration for a Virtual Machine is fundamental to optimizing its performance, data durability, and cost-effectiveness, directly impacting application responsiveness and reliability.

Scenario: You are deploying a Virtual Machine for a new SQL Server database. The database requires very high IOPS and low latency for its data files and log files. You also need to attach a separate, less performance-critical disk for backups.

What It Is: VM storage refers to the persistent disk space attached to an Azure Virtual Machine. Managed disks are recommended, as Azure handles their underlying storage account management.

Managed Disk Types:

• Ultra Disks: Highest throughput, lowest latency (sub-millisecond).
  • Use for: I/O-intensive, mission-critical workloads like SAP HANA, SQL, NoSQL databases.
• Premium SSDs: High performance, low latency.
  • Use for: Production and transactional systems, high-performance web servers.
• Standard SSDs: Cost-effective, consistent performance.
  • Use for: Web servers, dev/test, and lightly used apps.
• Standard HDDs: Lowest cost, for infrequent access, backup, or archival.
  • Use for: Infrequently accessed workloads, non-critical data.

OS Disk vs. Data Disks:

• OS Disk: Contains the VM’s operating system and boot files.
• Data Disks: Additional disks for application data, databases, or logs.

Host Caching:

• Read-only: Improves read performance for cached data.
• Read/Write: Boosts both read and write speeds but may risk data loss if the VM crashes.
• None: No caching; ensures maximum data durability, often used for write-heavy or critical data disks (e.g., database log files).

Visual: Azure VM Disk Types and Host Caching

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⚠️ Common Pitfall: Using a Standard HDD for the OS disk of a production VM. This can lead to slow boot times and poor overall system performance.

Key Trade-Offs:

• Performance (Premium/Ultra) vs. Cost (Standard): Premium and Ultra disks provide superior performance but are significantly more expensive than Standard disks.

Reflection Question: How does selecting the right managed disk type (e.g., Premium SSD for data, Standard HDD for backups) and configuring host caching (e.g., None for logs) fundamentally impact VM speed, reliability, and cost, ensuring optimal performance for critical database workloads?