> For the complete documentation index, see [llms.txt](https://docs.tibero.com/zetadata.en/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tibero.com/zetadata.en/failover.md).

# Failover

## **SSVR** Instance Failure

If an SSVR instance fails, the TAS instance automatically detects the status of the corresponding disk and performs I/O Fail-over. If each SSVR instance is configured with a FAILGROUP of 1:1, and the redundancy level of the disk space is NORMAL or higher, all loads performed on the DB will run normally regardless of the failure of one SSVR instance.

If a sSSVR instance recovers from a failure, then the TAS instance automatically detects the SSVR instance's status to synchronize all the disks in the SSVR instance . If it is impossible to perform a failover on a SSVR instance , then that SSVR instance can be removed from the disk space. To remove the SSVR instance, connect to the TAS instance to remove the FAILGROUP that corresponds to the storage server that is to be removed.

The following is an example of removing from a TAS disk space when the failed SSVR instance is in a FAILGROUP named FG0.

```sql
$ tbsql sys/tibero@tas0
SQL> alter diskspace DS0 drop disks in failgroup FG0 rebalance wait;
```

There must be enough free disk space left to store the data on all the disks you want to remove.

To add the newly configured SSVR instance, add FAILGROUP using the ALTER DISKSPACE syntax in TAS. 

The following is an example of adding the grid disk of a newly configured SSVR instance to a FAILGROUP named FG0 in a disk space.

```sql
$ tbsql sys/tibero@tas0
SQL> alter diskspace DS0 add failgroup FG0
disk '-10.10.10.11/GD0' name DISK0 size 64G, 
     '-10.10.10.11/GD1' name DISK1 size 64G
rebalance wait;
```

{% hint style="info" %}
**Note**

Failure of a flash device should be treated as an unrecoverable failure.
{% endhint %}

###

***

## **TAC** Instance Failure

If a TAC instance fails, sessions are recovered through the Fail-over feature of Tibero Active Cluster. 

For more information, refer to the "Tibero Administrator's Guide".

###


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