When backup solutions leverage Windows Volume Shadow Copy Service (VSS) without SQL Server awareness,
they essentially capture raw .mdf and .ldf files at a frozen moment. While SQL Server's storage engine
is designed for crash recovery, this approach differs fundamentally from native SQL backup mechanisms.

SQL Server's write-ahead logging ensures that transactionally consistent states can be reconstructed from:

1. The database file snapshot (MDF)
2. The corresponding log chain (LDF)
3. The active transaction log portion in memory

The recovery process mirrors what happens during server restart after a crash.

While technically recoverable, non-VSS-aware backups have significant operational constraints:

• No point-in-time recovery capability (only crash-consistent state)
• Potential log file growth if snapshot occurs during heavy transactions
• No built-in checks for page-level corruption
• Lack of metadata about backup timing in SQL Server's msdb

To validate a VSS snapshot backup, use this T-SQL after restoring files:

RESTORE DATABASE [TestRestore] 
FROM DISK = 'C:\backups\vss_snapshot.bak' 
WITH MOVE 'DataFile' TO 'C:\data\TestRestore.mdf',
MOVE 'LogFile' TO 'C:\data\TestRestore.ldf',
RECOVERY, REPLACE, STATS = 5;

DBCC CHECKDB ('TestRestore') WITH NO_INFOMSGS, ALL_ERRORMSGS;

The CHECKDB operation is particularly crucial for VSS-based backups.

For production environments, consider these VSS-aware approaches:

During snapshot creation, SQL Server experiences:

• Brief I/O freeze (typically < 2 seconds)
• Temporary transaction log growth
• Increased memory pressure from copy-on-write operations

Monitor with:

SELECT * FROM sys.dm_io_virtual_file_stats(NULL, NULL);
SELECT log_reuse_wait_desc FROM sys.databases;

When backup applications leverage Windows Volume Shadow Copy Service (VSS) without specific SQL Server awareness, they capture raw database files (MDF/NDF/LDF) at a single instant. SQL Server's storage engine is designed with crash recovery mechanisms that ensure transactional consistency even when files are copied mid-operation.

SQL Server uses write-ahead logging (WAL) and checksum verification to maintain database integrity. A VSS snapshot backup will typically result in a database that:

• Contains all committed transactions up to the snapshot moment
• Automatically recovers using the transaction log during restore
• May require recovery time proportional to transaction log size

While technically possible, several factors affect reliability:

-- Example check for database state after VSS restore
SELECT 
    name AS [Database],
    state_desc AS [State],
    is_in_standby AS [Standby]
FROM sys.databases
WHERE state != 0;  -- Check for non-online databases

VSS operations can cause temporary I/O freezes:

• Expect 2-10 second latency spikes during shadow copy creation
• Heavily loaded OLTP systems may experience timeouts
• Consider scheduling during low-activity periods

For mission-critical systems, combine VSS with:

-- Create a database snapshot for application-consistent backup
CREATE DATABASE Sales_Snapshot ON
(NAME = Sales_Data, FILENAME = 'D:\Backups\Sales_Data.ss')
AS SNAPSHOT OF Sales;

Always validate VSS backups using:

1. DBCC CHECKDB after restore
2. Point-in-time recovery tests
3. Transaction log chain verification