Attach vs Restore Database in SQL Server

Attach vs Restore Database in SQL Server:

Choose the Best One

In SQL Server, Attach and Restore are two methods used to make a database available, but they serve different purposes and use different processes.

Detach/Attach: This will be detaching database from the source server and then, one can attach or copy MDF and LDF files in the targeted server.

Backup/Restore: With help of this operation, take backup of the source SQL server database and restore it in the targeted server.

The above statements give an overview about the server migration activities but, the major problem is to decide the best one. 

 

Attach Database:

§  Purpose: Attach a database that already exists as physical files (MDF, LDF) on disk. This is typically used when you already have the database files available and want to reattach them to the SQL Server instance.

§  Process:

• SQL Server attaches the database by pointing to the existing MDF (data file) and LDF (log file) without performing any data recovery. It reads the metadata from the files and brings the database online.
• You can attach a database by using SQL Server Management Studio (SSMS) or the sp_attach_db or CREATE DATABASE ... FOR ATTACH T-SQL commands.

 

Use Case:

• Used when you move or copy the database files manually, such as after detaching a database, moving it to a new server, or recovering from a disk backup.
• Ideal for when the database was properly detached and the files are intact.

Pros:

• Quick process since no recovery is required.
• Can be used to move databases between SQL Server instances without creating a backup file.

Cons:

• Can only be used if you have access to the original physical files.
• If the log file (LDF) is missing or corrupt, SQL Server will attempt to rebuild it, but this could result in data loss.

 

Restore Database

Purpose: Restore a database from a backup file (a BAK file). This is a more comprehensive method that ensures all data recovery processes are executed.

Process:

• SQL Server restores the database from the backup file, re-creating the MDF, LDF, and optionally NDF (secondary files). During this process, SQL Server applies transaction log backups if any are available, and ensures the database is restored to a consistent state.
• Performed using SQL Server Management Studio (SSMS) or the RESTORE DATABASE T-SQL command.

Use Case:

• When you need to recover from a previous backup.
• Used for disaster recovery scenarios, creating database copies, or restoring databases on another server.
• Ideal for restoring databases to a specific point in time (using Full, Differential, and Transaction Log backups).

 

Pros:

• Comprehensive recovery process that includes applying transaction logs.
• Can restore from a point in time using full, differential, and transaction log backups.
• Ensures database consistency after restore.

Cons:

• Slower than attaching, as the database is recreated from the backup.
• Requires a backup file (BAK), which can be larger in size.

 

Summary:

• Attach is faster and useful when you have the original database files intact and need to move or reattach them.
• Restore is the go-to method for recovering from a backup file, ensuring data integrity and recovery to a specific point in time. It is typically more secure and comprehensive.

 

Difference Between Attach vs Restore Database in SQL Server

Attributes	Attach/Detach SQL Server Database	Backup & Restore SQL Server Database
Description	The operation involves simple attachment of secondary SQL server database file with primary one	The operation involves restoration of all items from the SQL server database backup file.
File Format of Source SQL Database File	Here, the source file for attachment is in MDF format.	The SQL server backup file from which items are to be restored is in BAK format.
Required Mode	This activity is carried out in an offline mode. It means that the source database must be in inactive status.	It requires online or active mode for the successful finishing up of the task.
Total Time Required	The time taken in attaching the SQL database is as such not dependent on file size. Basically, it is same as the time required in copying data files and log from one server to the another.	Restoration time of database is equivalent to 3 times of the backup time. Talking about the migration from one server to another then, time will be overall combination of backup time, restoration time and then the time required in server migration.
SQL Server Log File Presence	If in case the size of server log file is huge then, users need to copy the all the records over the network. However, if you are not having the log file then also you can simply attach MDF file and continue with the server migration.	The backup file size does not include any kind of data log file size aspect.
Fragmented Data Files	It would be of no worth, if you are carrying attach option on fragmented data files. It is so because this activity will carry unwanted additional data bytes, which are totally of no use.	The SQL BAK file comprises of the pages, which are already used in the server. So, here the size concern is quite close to the size of used data files.
Maintenance of the SQL Server Activity Record	There is no record maintained for the detach or attach operation in the SQL server. So, no procedure details like procedure time, where were the files attached, etc., are stored in MSDB database.	The procedure of backup and restoration in the SQL server is stored in MSDB database tables. This table comprises of information like date, size, backup / restore type, etc.
Equipped Additional Options	No other additional options area available to move data from one server to another.	Users are provided with advance options like partial backup, mirrored backup, time recovery point, etc., in this migration measure.