Level 1 to 9 backups are not supported for snapshot backups.

What is the SQL Server Version? Windows Version? NetWorker Version and NMM Version?

SQL : 2008 R2

Windows :server2008r2

NMM:8.2.1.4

Is it VDI or VSS backup?  I assume VDI as you mentioned logs   Anyway, truncating is kind of slippery terrain in SQL (see http://www.brentozar.com/archive/2009/08/backup-log-with-truncate-only-in-sql-server-2008/ and Transaction Log Truncation). I don't use differential level, but rather only full and incr, but I would assume differential level is not involved in any truncation.

Truncation of SQL log files will only be done by a SQL log-backup which translates to a NetWorker level incremental backup.

Neither a NetWorker level 1 backup (which translates to a database differential backup in SQL) nor a level full backup will do this.

Please check out the link Hrvoje mentioned above. There are links at MS sites available telling similar.

When using VDI backup technologie you will be able to do a level incr backup from NetWorker.

When using VSS snapshot technologie you will be able to perform level full backup only, so no incremental backup is available and no SQL log truncation will occure.

Please share with us what backup technologie is used so we can help more accurate.

hth

Thanks a lot for this information

it is VDI Backup