# Extreme High Availability

+ TiDB Dedicated is designed to be always-on for applications in the events of:
  + Unplanned system or availability zone failures
  + Planned maintenance operations, such as patching and upgrading

![`smart`](TiDBCloudProviderRegion_aa_003_20220524.png)

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TiDB Dedicated is always-on and always-up out-of-the-box. It provides built-in components High Availability and availability zone redundancy.

The following unplanned underlying failures do not hinder the availability of the TiDB service as a distributed database:
- Minority server instances failure
- Minority server hardware failure
- Minority TiDB components (such as TiDB server, TiKV server and Placement Driver server, etc) failure
- Minority availability zone failure

The following planned maintenance operations do not hinder the availability of the TiDB service as a distributed database:
- Applying database patches
- Upgrading database versions

The following public videos on Youtube showcase the near zero downtime high availability ability of TiDB by utilizing a self-hosted instance of TiDB on the public cloud.
- TiDB Quick Demo - Achieving Zero Downtime During Online Upgrade: `https://www.youtube.com/watch?v=HLrIwbMgOhg&list=PLl-T_1b242uWedcYP5ZK1y1rMZUkTp2bz&index=1`
- TiDB Quick Demo - Achieving Zero Downtime Under availability zone Failure: `https://www.youtube.com/watch?v=3gY4-cTDqiE&list=PLl-T_1b242uWedcYP5ZK1y1rMZUkTp2bz&index=4`