Many administrators assume that full VM backups eliminate the need for transaction log backups in SQL Server. However, the transaction log serves three critical functions that go beyond simple recovery:

-- Basic transaction log backup command
BACKUP LOG [YourDatabase] 
TO DISK = N'C:\Backups\YourDatabase_Log.trn'
WITH COMPRESSION, STATS = 10;

Full database backups alone cannot provide minute-level recovery. Transaction logs enable:

• Recovery to any specific point in time (e.g., 2:15 PM before the corruption occurred)
• Rollforward of committed transactions after restoring a full backup
• Rollback of uncommitted transactions during recovery

While VSS-aware backups like ArcServe UDP capture database files, they typically:

-- Check log space usage (shows why truncation matters)
DBCC SQLPERF(LOGSPACE);
GO

-- View log reuse wait reasons
SELECT name, log_reuse_wait_desc 
FROM sys.databases;
GO

VSS backups often don't properly mark log space as reusable, leading to uncontrolled log growth over time.

Consider this sequence that only transaction logs can solve:

1. Full backup at 12:00 AM
2. Corruption occurs at 3:15 PM
3. You need data as it existed at 3:14 PM

-- Sample point-in-time restore sequence
RESTORE DATABASE [YourDB] FROM DISK = 'C:\Backups\Full.bak' 
WITH NORECOVERY, REPLACE;

RESTORE LOG [YourDB] FROM DISK = 'C:\Backups\Log1.trn' 
WITH NORECOVERY;

RESTORE LOG [YourDB] FROM DISK = 'C:\Backups\Log2.trn' 
WITH STOPAT = '2024-02-20 15:14:00', RECOVERY;

Without explicit log backups, the log continues growing because:

• SQL Server maintains logs for potential rollback operations
• Active transactions may span multiple backup cycles
• Some operations like index rebuilds are fully logged

-- Complete backup plan example
-- Full backup nightly
BACKUP DATABASE [YourDB] TO DISK = 'C:\Backups\Full.bak'
WITH COMPRESSION, CHECKSUM;

-- Differential every 4 hours
BACKUP DATABASE [YourDB] TO DISK = 'C:\Backups\Diff.bak'
WITH DIFFERENTIAL, COMPRESSION, CHECKSUM;

-- Log backup every 15 minutes
BACKUP LOG [YourDB] TO DISK = 'C:\Backups\Log.trn'
WITH COMPRESSION, CHECKSUM;

SQL Server's transaction log isn't just an audit trail - it's the backbone of ACID compliance. When you execute a transaction, SQL Server first writes to the log (WAL protocol) before modifying data files. This ensures recoverability even if the server crashes mid-operation.

While ArcServe UDP with VSS provides point-in-time recovery, consider these scenarios:

-- Scenario 1: Corrupt page at 2:05 PM
-- Full backup at 2:00 PM + log backups = recover to 2:04 PM
-- VM snapshot at 2:00 PM only = lose 4 minutes of data

-- Scenario 2: Accidental DELETE at 1:58 PM
-- Log backup lets you perform STOPAT recovery
RESTORE DATABASE ERP_DB 
FROM DISK = 'C:\Backups\ERP_Full.bak' 
WITH NORECOVERY, REPLACE;

RESTORE LOG ERP_DB 
FROM DISK = 'C:\Backups\ERP_Log.trn' 
WITH STOPAT = '2023-11-15 13:57:00', RECOVERY;

Log truncation isn't just about space management - it's about recovery chain integrity. When you perform:

BACKUP LOG ERP_DB TO DISK = 'C:\Backups\ERP_Log.trn'
WITH COMPRESSION, CHECKSUM;

SQL Server marks VLFs as reusable only after the log backup completes. Without this, the log grows indefinitely until you hit max size.

Imagine your ERP database gets corrupted during a failed index rebuild:

-- 1. Tail log backup (critical!)
BACKUP LOG ERP_DB TO DISK = 'C:\Backups\ERP_Tail.trn'
WITH CONTINUE_AFTER_ERROR;

-- 2. Restore sequence
RESTORE DATABASE ERP_DB 
FROM DISK = 'C:\Backups\ERP_Full.bak' 
WITH NORECOVERY, REPLACE;

RESTORE DATABASE ERP_DB 
FROM DISK = 'C:\Backups\ERP_Diff.bak' 
WITH NORECOVERY;

RESTORE LOG ERP_DB 
FROM DISK = 'C:\Backups\ERP_Log_Sequence.trn' 
WITH RECOVERY;

Configure your backup jobs like this:

-- Full backup weekly
BACKUP DATABASE ERP_DB 
TO DISK = 'C:\Backups\ERP_Full_$(ESCAPE_NONE(DATE)).bak'
WITH COMPRESSION, CHECKSUM, STATS = 10;

-- Differential daily
BACKUP DATABASE ERP_DB 
TO DISK = 'C:\Backups\ERP_Diff_$(ESCAPE_NONE(DATE)).bak'
WITH DIFFERENTIAL, COMPRESSION, CHECKSUM;

-- Log backup every 15 minutes
BACKUP LOG ERP_DB 
TO DISK = 'C:\Backups\ERP_Log_$(ESCAPE_NONE(DATE))_$(ESCAPE_NONE(TIME)).trn'
WITH COMPRESSION, CHECKSUM;