In the event that an HDB file is taken offline, a file recovery process may be needed to recover the data and put the file back online. A file may be taken offline if it is open for writing during a hard shutdown, the timestamp of a tag moves in a backward direction from one file to the next (this can happen if manually moving files from one historian to another), or some other file corruption caused by the file system or a historian crash. An offline file will appear as a gray tile within the dataset. In order to recover it:

1. Select the offline file
2. Click the yellow down-arrow in the FILE menu
3. Select RECOVER

The recovery process goes through four phases in creating a new file. During this process the historian attempts to correct and recover any corrupted data as well as trim any overlapping timestamps that may occur between files.

Once recovered, the new file will be placed back online. The old file is retained but is renamed using a .old extension in the directory.

It is recommended that once the file is recovered it be validated to ensure that it stays online. A file can be validated using the same drop-down arrow from the FILE menu. If it passes the validation process no more action is required. If, however, the validation process finds an issue it will place the file offline and report an error in the validation window. In this case, contact support@canarylabs.com as it may require further troubleshooting and we will need the old and new file and its adjacent files to analyze.

Overlapping Timestamps

As stated above, one of the reasons a file is taken offline is if the timestamps of a tag(s) overlap from one file to the next. This tag(s) can be determined by putting the file online and running the validation process. The validation window will reveal the tag and timestamps which are not in chronological order. The user may wish to examine both files before determining which one to recover as the recovery process will trim out the timestamps of the file that is being recovered.

If needing to revert back to the old file, the new file can be taken offline and deleted. Remove the .off.old extension of the old file, then select 'REFRESH FILE LIST' within the DATASET OPTIONS menu.