Inconsistent File Size Errors During Restore

michaeldolzani

Hello,
I’m encountering intermittent file size mismatch errors during restore operations with Bacula. The error message is as follows:
• Error: attribs.c:614 File size of restored file /var/log/mysql/mysql-bin.000115 not correct. Original 91146521, restored 91165346.
• Error: attribs.c:614 File size of restored file /var/log/syslog not correct. Original 14576827, restored 14577192.

Environment:
• Architecture: Centralized backup system with one main server (Director, Storage Daemon, and Catalog) managing backups for multiple client servers (File Daemons).
• Restore Process: Restores are performed to a local directory on the central backup server.
• Storage: Sufficient disk space is available on the restore target.
• Network: No connectivity issues observed; restores are local to the central server.

Observations:
• The issue occurs with several client servers but not all.
• Backup jobs complete without errors; discrepancies are only noted during restore.

Questions:
1. What causes these file size mismatch errors during restore?
2. How can I prevent or handle these errors effectively?
3. Are there best practices for backing up files that are actively written to, like logs or database binaries?

Thanks

gani

Hello @michaeldolzani,

michaeldolzani 1. What causes these file size mismatch errors during restore?

This error is displayed during restore but the real mismatch happened during backup. This happens if file was changed during backing it up. It does not need to mean problems because Bacula first gets a given file attributes and then it does the file data backup and at the end Bacula checks if the file has changed during backup. You can read about this error here (file size error):

https://www.bacula.org/15.0.x-manuals/en/main/Restore_Command.html#SECTION00301100000000000000000

If you have Check File Changes directive enabled in job fileset options block (default it is enabled) then in the backup job log you should see message that the backed up file size changed:

https://www.bacula.org/15.0.x-manuals/en/main/Configuring_Director.html#13208

In other words, this error happens if the size value written in the catalog database is different than the real backed up file. I think this situation can be also detected by Verify type job.

michaeldolzani 2. How can I prevent or handle these errors effectively?

(if possible) doing backup from volume snapshot will prevent it.
(if possible) doing backup in a time window when there is not too many write operations in systems will reduce it.

michaeldolzani 3. Are there best practices for backing up files that are actively written to, like logs or database binaries?

In case databases or virtual machines you can check if the database server or vm server provides tools that can be helpful for backup.

Best regards,
Marcin Haba (gani)