Full disk lock

The full disk lock function of KubeBlocks ensures the stability and availability of a database. This function triggers a disk lock when the disk usage reaches a set threshold, thereby pausing write operations and only allowing read operations. Such a mechanism prevents a database from being affected by disk space exhaustion.

Mechanism of lock/unlock

When the space water level of any configured volume exceeds the defined threshold, the instance is locked (read-only). Meanwhile, the system sends a related warning event, including the specific threshold and space usage information of each volume.

When the space water level of all configured volumes falls below the defined threshold, the instance is unlocked (read and write). Meanwhile, the system sends a related warning event, including the specific threshold and space usage information of each volume.

Enable full disk lock

• For MySQL, the read/write user cannot write to the disk when the disk usage reaches the highwatermark value, while the superuser can still write.
• For PostgreSQL and MongoDB, both the read/write user and the superuser cannot write when the disk usage reaches highwatermark.
• 90 is the default value setting for the high watermark at the component level which means the disk is locked when the disk usage reaches 90%, while 85 is used for the volumes which overwrites the component's threshold value.

Steps:

1. Edit the ClusterDefinition Custom Resource (CR) of a database.

   This guide takes mysql as an example. You can replace mysql with postgresql or mongodb.

   kubectl edit clusterdefinition mysql
   

2. Add the volumeProtectionSpec field under spec.componentDefs[] to enable the full disk lock function. You can set the values of highWatermark as needed.

   ...
   spec:
     componentDefs:
     ...
     - name: mysql
       volumeProtectionSpec:
         highWatermark: 90
         volumes:
         - highWatermark: 85
           name: data
     ...
   

   NOTE

   The recommended value of highWatermark is 90.

3. Save the changes and exit.

Disable full disk lock

To disable the full disk lock function, just delete the volumeProtectionSpec field from the ClusterDefinition CR.

Steps:

1. Edit the ClusterDefinition CR of a database.

   This guide takes mysql as an example. You can replace mysql with postgresql or mongodb.

   kubectl edit clusterdefinition mysql
   

2. Delete the volumeProtectionSpec field.

3. Save the changes and exit.