Azure Storage — Azure DocumentDB
Azure DocumentDB clusters use remote premium SSD storage. Two disk types are offered:
| Storage type | IOPS / bandwidth scaling | Max IOPS | CMK | Use it for |
|---|---|---|---|---|
| Premium SSD (v1) | Scales with disk capacity — bigger disk → higher IOPS | 20,000 | ✔️ | Legacy clusters, scenarios that require CMK |
| Premium SSD v2 | Decoupled from disk size — IOPS/bandwidth gated by compute tier | 80,000 | ❌ | New production clusters; any I/O-intensive workload |
Premium SSD v2 is the default recommendation for new clusters. It delivers up to a 12× performance boost at no added cost by removing the disk-size lever from the IOPS equation — you size storage for capacity and size compute for throughput, independently.
How Premium SSD v2 changes sizing
On Premium SSD v1, hitting 20,000 IOPS required provisioning a 20 TB disk even when only ~1 TB of data was stored. On Premium SSD v2, the highest achievable IOPS and bandwidth for the chosen compute tier are auto-configured regardless of disk size:
- Choose storage size based on how much data the cluster will hold.
- Choose compute tier based on how much IOPS / MBps the workload needs (see storage-tier-iops-caps).
- No knobs to tune — the upper-bound IOPS/bandwidth for the tier are applied automatically at no extra cost.
Rules
- storage-choose-premium-ssdv2 — When to pick Premium SSD v2 vs Premium SSD; the CMK trade-off.
- storage-tier-iops-caps — Compute-tier → max IOPS / MBps table; size compute for throughput, not disk for IOPS.
- storage-premium-ssdv2-limitations — Known limits: no CMK, capacity-change cap, replication restrictions, no online v1→v2 migration.
- storage-disk-hydration-sequencing — Space out compute scale / storage scale / HA-enable operations while the disk is hydrating.