Database Snapshot

This is the New product Introduced in SQL Server 2005.A database snapshots allow you to create a point-in-time, read-only copy of any database.Multiple snapshots can be created for the same source database at different points in time.The actual space needed for each snapshot is normally much less than the space required for the original database because the snapshot stores only pages that have changed.

Microsoft has finally added database snapshots to its database store.Database have been a part of challenging products (ORACLE & DB2) for years.
Keep in mind that database snapshots are point-in-time and read-only.System Databases cannot be created for Database Snapshot.
Database snapshots make huge use of Microsoft’s copy-on-write technology
The database snapshot feature is available only with the Enterprise Edition of SQL Server 2005.
Database snapshots allow you to do the following:
They decrease recovery time of a database because you can restore a troubled database with a database snapshot
They create a safeguard previous to running mass updates on a critical database.
They provide a read-only, point in time reporting and off-loaded database.
Protect against administrative or user errors.

How to create a Database Snapshot :The mechanics of snapshot creation are straightforward—you simply specify an option for the CREATE DATABASE command. There is no graphical interface for creating a database snapshot through Object Explorer, so you must use the T-SQL syntax.

Limitations and Restrictions :
You must drop all other database snapshots when using a database snapshot to revert a source database.
The more updates to pages in the source database, the bigger your database snapshot sparse files become.
A database snapshot can only be done for an entire database, not for a subset of the database.
No additional changes can be made to a database snapshot. It is read-only and can’t even have additional indexes created for it to make reporting queries run faster.
Additional overhead is incurred on update operations on the source database due to the copy-on-write technique (only when something changes, though).
If you’re using a database snapshot to revert (restore) a source database, both the snapshot and the source database are not available.
The source database cannot be dropped, detached, or restored until the database snapshot is dropped first.
Files on the source database or the snapshot cannot be dropped.
In order for the database snapshot to be used, the source database must also be online (unless the source database is a mirrored database)
The database snapshot must be on the same SQL Server instance as the source database.
Database snapshot files must be on NTFS only (not FAT 32 or RAW partitions)
Full-text indexing is not supported.
If a source database ever goes into a RECOVERY_PENDING status, the database snapshot also becomes unavailable.
If a database snapshot ever runs out of disk space, it must be dropped; it is actually marked as SUSPECT.
You must drop all other database snapshots when using a database snapshot to revert a source database.