SQL Database Tiers & Compute
DTU vs vCore · General Purpose · Business Critical · Hyperscale · Serverless · Free offer
Practice questions for this topic →
Purchasing models
| DTU | vCore (recommended) | |
|---|---|---|
| Resources | Bundled compute + storage + I/O | Choose compute and storage independently |
| Tiers | Basic, Standard, Premium | General Purpose, Business Critical, Hyperscale |
| Azure Hybrid Benefit / reservations | No | Yes (provisioned compute only) |
| Serverless | No | Yes (General Purpose and Hyperscale, Standard-series Gen5) |
vCore service tiers
| Tier | Architecture | Pick when… |
|---|---|---|
| General Purpose | Compute separate from remote storage | Most workloads; budget-oriented; no replicas in the HA design |
| Business Critical | Replicas on local SSD (Always On style) | Low-latency OLTP, fast failover, free read scale-out replica, in-memory OLTP |
| Hyperscale | Distributed compute with page servers; snapshot backups | Very large or fast-growing DBs beyond 4 TB, fast backups and restores, HA and named replicas |
Serverless compute
| Fact | Detail |
|---|---|
| Best for | Intermittent, unpredictable usage that tolerates a warm-up delay |
| Auto-pause | GA in General Purpose (minimum delay 15 minutes, default 60); preview in Hyperscale (minimum 60) |
| Starts only when | Zero sessions and zero user-workload CPU for the whole delay |
| Blocks auto-pause | Geo-replication, failover groups, long-term backup retention, DNS alias, open sessions |
| Auto-resume triggers | Login attempts, threat-detection settings changes, sensitivity-label changes, viewing auditing records |
| Billing | Per-second compute while active; storage only while paused. No Azure Hybrid Benefit or reservations |
| On resume | The first connection may fail with error 40613, so use retry logic |
Free offer (Microsoft Learn)
| Item | Detail |
|---|---|
| Allowance | Up to 10 General Purpose databases per subscription; per database each month: 100,000 vCore seconds, 32 GB data, 32 GB backup. Free for the life of the subscription, no time limit |
| Limits reached | 'Auto-pause until next month' makes the database inaccessible until the next calendar month; change the option to continue with charges |
| Gotchas | No SLA (development and proof of concept); you can't restore into a free database; leaving SSMS or Object Explorer connected prevents auto-pause and burns credits |
Exam Tips
Tick each tip once you can answer it without looking.
“Dev/test database idle most of the day, minimize cost” → Serverless (General Purpose) with auto-pause.
“Serverless database never pauses” → It's in a failover group/geo-replication or has LTR configured.
“Database will grow to 50 TB, needs fast restores” → Hyperscale.
“Lowest latency OLTP with free read replica for reporting” → Business Critical (ApplicationIntent=ReadOnly).
“Use existing SQL licenses + 3-year commitment for steady workload” → vCore provisioned + Azure Hybrid Benefit + reserved capacity. Trap: Serverless and DTU can't use these.
“Simple fixed-price small database” → DTU Basic/Standard.
“Hyperscale read replicas for heavy, isolated reporting workloads” → Hyperscale named replicas (billed separately). Trap: Only Premium/Business Critical include a free replica.
“Steady 24×7 production load” → Provisioned compute. Trap: Serverless costs more per vCore-hour when always busy.
“What resumes a paused serverless database” → A login attempt, changing threat detection settings, sensitivity label changes, or viewing auditing records. Trap: The first connection may fail with error 40613, so use retry logic.
“Azure SQL Database free offer limits” → Up to 10 General Purpose databases per subscription, each with 100,000 vCore seconds, 32 GB data and 32 GB backup per month, free forever. Trap: No SLA; for development and proof of concept.
“Free database never auto-pauses” → Open sessions (for example SSMS Object Explorer) keep consuming vCore seconds. Trap: Auto-pause starts only with zero sessions and no user CPU for the delay.
“Free offer exhausted with 'auto-pause until next month' set” → Database is inaccessible until the next calendar month unless you enable billing past the free amount. Trap: You can upgrade the tier at any time.
“Restore an existing database into a free-offer database” → Not allowed: free databases are for new databases. Trap: Deleting a free database frees its slot after about an hour.