Summary the high availability technologies offered by SQL Server 2008.

<!-- [if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:DrawingGridVerticalSpacing>7.8 磅</w:DrawingGridVerticalSpacing> <w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery> <w:DisplayVerticalDrawingGridEvery>2</w:DisplayVerticalDrawingGridEvery> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:SpaceForUL/> <w:BalanceSingleByteDoubleByteWidth/> <w:DoNotLeaveBackslashAlone/> <w:ULTrailSpace/> <w:DoNotExpandShiftReturn/> <w:AdjustLineHeightInTable/> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> <w:UseFELayout/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!-- [if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!-- [if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:普通表格; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]-->

Summary the high availability technologies offered by SQL Server 2008.

1. Federated Databases.

2. Failover Clustering

3. Mirror Database

4. Peer to peer Replication

==================================================

1.Federated database is a collection of independent servers.Connected by a LAN.

The data is distributed across each participating server.

The application see a logical single view of data through UNION ALL views.

The application know which data in the view is local and which is remote.

To avoid creating a hot node the DBA need to know how to partition and distribute the data.

If one node failure then need DBA to take offline the data on the node.

It does not provide the complete availability.

2.Failover Clustering is a group of SQL Server database acts just like a single SQL Server database.

The clustering does not provide additional scalability. The database only runs on 1 node.once this node fails all connections to this database are lost.

The new connection has to wait restart the SQL server database on a surviving nodel.

The application need to reconnect and restart their transactions.

The procedure is complex and take rather long time and also the standby node has nothing to do if the primary node work well.

3.Mirror Database

The SQL Server database provide more than one warm standby site through log shipping.

Mirror Database does not provide any kind of scalability.

The availability of it is similar to Oracle Data Physical Guard.

The Mirror Database is in unavailable state to application until a failover occurred automitically or manually.

4.Peer to Peer Replication

The Replication can move data in both ways,act as a bi directional replication.

It also provide the load balance workload across more than one database server.

It does not provide any scalability.It provide the conflict detection and conflict resolution since it is bidirectional replication.

The data is reducdent distributed across all the participating server.