Disks and Storage¶
Azure VM storage uses managed disks with different latency, IOPS, and throughput characteristics. Correct disk type and caching choices are critical for both performance and durability.
Disk Types¶
| Disk Type | Description | Persistence | Recommended Use |
|---|---|---|---|
| OS Disk | Contains operating system files | Yes | Boot and system state |
| Data Disk | Persistent application storage | Yes | Databases, app data, logs |
| Temporary Disk | Local host storage | No | Page/swap, temp, scratch data only |
Managed Disk Tiers¶
| Tier | IOPS (Max) | Throughput (Max) | Typical Profile |
|---|---|---|---|
| Ultra Disk | Up to 400,000 | Up to 10,000 MB/s | Highest performance, low latency |
| Premium SSD v2 | Up to 80,000 | Up to 1,200 MB/s | High performance, flexible provisioning |
| Premium SSD | Up to tier limit | Up to tier limit | Production transactional workloads |
| Standard SSD/HDD | Lower | Lower | Cost-optimized general workloads |
Host Caching Guidance¶
Warning
Ultra Disk and Premium SSD v2 do not support host caching (ReadOnly or ReadWrite). These disk types use their own performance architecture, so host caching settings are not applicable.
| Disk Role / Workload | Default Caching | Recommended Caching | Why |
|---|---|---|---|
| OS Disk | ReadWrite | ReadWrite (default) | Improves boot and OS read/write responsiveness |
| Data Disk (general default) | None | None (default) | Safe baseline for mixed and write-sensitive workloads |
| Read-heavy data (reference/catalog/reporting) | None | ReadOnly | Improves repeated reads |
| Write-heavy data or DB transaction logs | None | None | Avoids added write latency and crash-consistency risk |
| Apps with explicit durable flush behavior | None | ReadWrite (case-by-case) | Only when the app correctly handles flush/ordering |
Managed Disk Hierarchy¶
graph TD
MD[Managed Disk] --> U[Ultra Disk\nHighest performance tier]
MD --> PV2[Premium SSD v2\nHigh performance, flexible]
MD --> P[Premium SSD\nHigh performance]
MD --> S[Standard SSD\nBalanced cost/performance]
MD --> H[Standard HDD\nLowest cost tier]