Data Backup and Recovery

Transaction Log backups LSN values





Do anyone has good understanding of TLOG backups[.trb files] which are created as part of SMSQL.

I need some info on how the first LSN,Last LSN values are calculated and how this effects the log chain.


In what cases can the chain break..


I have a situation where 3 log backups has same First LSN and different Last LSN.what is this mean?









TRB basically means transaction log backup


A transaction log backup is a record of the database changes that have occurred since the last transaction log backup. SnapManager supports transaction log backups in order to provide a more granular level of database backup and to recover the transactions committed since the most recent full backup.

SnapManager creates a backup of a transaction log by copying transaction log data to a file in the SnapInfo directory. Transaction log backup files are named using the following convention:



from here


Every record in the SQL Server transaction log is uniquely identified by a log sequence number (LSN). LSNs are ordered such that if LSN2 is greater than LSN1, the change described by the log record referred to by LSN2 occurred after the change described by the log record LSN.


So, as far as i know if yiu have the same LSN means that there weren't any changes in the database




In SMSQL new-backup cmdlet which is executed via powershell has a parameter named  -trunclog which can have parameters true/false.


When set to true we are having tlog backups forming a chain.

Whereas when set to false tlog backups no longer form a chain and not able to restore to point in time.


What is truncate log means when doing tlog backp and what happens when set to false?