The CrashPlan app stores information about your file selection and the progress of your backup in its cache files. To verify the accuracy of the cache files, the CrashPlan app periodically synchronizes this information with the information stored at the backup destination.
What happens during synchronization?
The CrashPlan app cache contains indexes with detailed information on all of the files, versions, and blocks of data you’ve backed up. During synchronization, the CrashPlan app repairs any mismatches between the local cache and your backup archive's cache on the CrashPlan server. The CrashPlan app then updates the cache and uses the updated information to complete your backup.
During synchronization, you cannot back up or restore using the CrashPlan app. See our troubleshooting article for more information and a temporary workaround.
When does synchronization occur?
By default, the CrashPlan app synchronizes your local cache with your backup at the beginning of each backup session, or when reconnecting to the CrashPlan server. Other actions that trigger synchronization include:
- Changing the file selection
- Adding a backup set
- Replacing a device
- Ejecting and reconnecting an external drive within your backup selection
See the synchronization process
Normally the synchronization process runs quickly and you may not notice that it has occurred. If your backup selection or archive are very large, then you may see the following process within the CrashPlan app when one of the triggers above begins the synchronization process:
- From Home in the CrashPlan app, Synchronizing is displayed under the progress bar.
The CrashPlan app compares the cache indexes. If they do not match, it downloads them from the server.
- File synchronization runs.
The CrashPlan app displays Synchronizing file information (0-100.0%).
- Block synchronization runs.
The CrashPlan app displays Synchronizing block information (0-100%).
- Backup and restore resume normally.