Epochs is a mechanism to decrease VDisk repair time. It works by periodically flushing (e.g. every 4 hours) a changed block bitmap of an online VDisk on the backend. If the VDisk needs to be repaired, the latest common epoch between the master and the slave is determined and then all subsequent epochs on the master are collapsed onto the latest common epoch bitmap. The resulting bitmap is effectively a diff bitmap, so only the blocks indicated into that bitmap need to be re-synchronized. If any error occurs during VDisk repair, the epochs optimization is disabled and VDisk repair switches to full re-synchronization.
To enable epochs for a data store:
- Go to your Control Panel > Admin > Settings menu.
- Click the Data Stores icon. You'll see a list of the data stores on your system.
- Click the Actions button next to the store you want to change, then click Edit.
- On the following page move the Epoch slider to the right to enable epochs.
- Click the Save Data Store button to finish.