The file verification scan inspects your file selection for any new, changed, or deleted files. This scan provides a second method for the CrashPlan app to detect file changes that the operating system's real-time file watching may have missed.
What does the file verification scan do?
When the file verification scan begins, a synchronization process compares the cache indexes at the source with the destination. The file verification scan then examines the locations selected for backup. If the scan detects any new, changed, or deleted files, those changes are added to the to-do list, then backed up to your archive at the destination. On Mac devices, the file verification scan is the only time the CrashPlan app removes deleted files from the backup archive.
When does the file verification scan occur?
By default, the scan is set to automatically run every day, but this schedule can be changed by updating the Preferred time for verification scan setting in device backup settings. The CrashPlan app periodically runs additional verification scans to detect data corruption, purge files that are no longer selected for backup, and prune file versions and deleted files according to your frequency and version settings.
In addition, there are times when a file verification scan is automatically triggered:
- Changing the file selection: If you update your backup file selection, either to add or remove files, the scan runs to look for new, changed, or deleted files.
- Replacing your device: After replacing a device (for example, if you recently changed devices), the scan runs to compare the files on your device to the files in your existing backup archive.
- Clearing your cache: The cache includes information about your destinations and the data on your device. When the cache is cleared, a file verification scan initiates to help rebuild this information.
- Attaching an external drive: When you attach an external drive, the scan runs to compare the files on the drive to the files in your existing backup archive.
- At device reconnection: If the device is powered off or asleep at the scheduled scan time, the scan runs 15 minutes after the device reconnects.
- Manually: The file verification scan can be triggered at any time from the Backup Set Settings Menu.
What does a file verification scan look like?
Initially, the CrashPlan app displays a message on the Backup tab that reads, "Scanning." If this initial scan determines that there have changes to the files, the file verification scan starts.
This file verification scan may look like your backup is starting over because the estimated time to complete doesn't account for the data that has already been backed up. During the file verification scan, the CrashPlan app compares each block in your file selection to the blocks that have already been backed up in your archive. Once the blocks have been analyzed, the CrashPlan app only backs up the differences.
Verification and backup is prioritized as follows:
- Newer, smaller files
- Newer, larger files
- Older, smaller files
- Older, larger files
How long does a file verification scan take?
The file verification scan normally runs within minutes and most users do not notice it. The larger your file selection, the longer the file verification scan takes. Although the scan may take longer for large backups, it is much faster than backing up the files. The estimated time to complete the file verification scan initially reports the time it would take to back up all files, but drops sharply once it finishes backing up new files and starts de-duplicating the data that is already backed up.
During your initial backup, you may wish to set the scan to run less often, as it can consume a significant amount of time that could otherwise be used to continue the backup. Keep the scan intervals reasonable (for example, every 30 days during a large initial backup). If you set the value too high, like every 10,000 days, the value overflows and the CrashPlan app ends up running the scan daily, which is the opposite of what you want!