Helpful to remember the diff between the trans log (huge single .LDF file prob in MSSQL\Log dir) and trans log backup files (.TRN files saved off the main mssql drive).
- Log backups are necessary to recover when the log drive has gone down (which could be any time, so single LDF file goes down, we still have the daily log backup as a starting point and all the TRN files since that).
- The trans log is truncated every time it is backed up - meaning all the TRN files must be chained together to be able to recover from the last full db backup.
- A common frequency for OLTP systems log backup is 10-15 mins. - TRN files.
- This only happens when db NOT in SIMPLE recovery mode.
- A full db backup (data file - nothing to do with trans log) means any trans log or their backups are redundant.