Redundancy and Availability
“Redundancy refers to the use of multiple servers in a
load-balanced environment for any of several purposes,
such as to improve farm performance, to scale out to
accommodate additional users, and to improve availability.”
“Availability is a more specialized concept that refers to a
multiple-server environment that is designed to accept
connections and operate normally even when one or more
of the servers in the farm are not operational.”
SharePoint 2007 Redundancy
Application Server Role Can be Redundant?
Web Role Yes
Query Role Yes
Index Service Role No*
Windows SharePoint Services 3.0 No
Excel Calculation Services Yes
Number of Nines
Acceptable uptime Downtime Downtime Downtime
percentage per day per month per year
95 72.00 minutes 36 hours 18.26 days
99 14.40 minutes 7 hours 3.65 days
99.9 86.40 seconds 43 minutes 8.77 hours
99.99 8.64 seconds 4 minutes 52.60 minutes
99.999 0.86 seconds 26 seconds 5.26 minutes
Recovery Time Objective (RTO). RTO is the
allowable duration that an application can be down.
Recovery Point Objective (RPO). RPO is the
amount of data loss that the customer can tolerate.
Cannot Connect to ….
The dreaded “Cannot connect to the database
server…or configuration database…”
SQL Clustering – availability at the SQL instance
SQL Mirroring – availability at the database.
* Mirroring available with SQL 2005 SP1
Database Mirroring Best Practices and Performance Considerations. Microsoft(r) TechNet. [Online]
March 10, 2006. [Cited: 10 09, 2008.]
Case Study of High Availability for SharePoint using Database Mirroring (white paper). Microsoft
TechNet. [Online] April 2008. [Cited: September 22, 2008.] http://technet.microsoft.com/en-
Microsoft. How to transfer the logins and the passwords between instances of SQL Server 2005.
Microsoft Help and Support. [Online] July 11, 2006. [Cited: October 13, 2008.]
Microsoft. Using Database Mirroring with Office SharePoint Server and Windows SharePoint
Services. Microsoft TechNet. [Online] July 24, 2008. [Cited: October 13, 298.]
Talmage, Ron. Database Mirroring in SQL Server 2005. Microsoft TechNet. [Online] April 1, 2005.
[Cited: October 14, 2008.] http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx.
Microsoft. Setting Up Login Accounts for Database Mirroring. MSDN: SQL Server Developer Center.
[Online] September 2007. [Cited: October 14, 2008.] http://msdn.microsoft.com/en-
Curry, Ben and English, Bill. Microsoft Office SharePoint Server 2007 Best Practices. Redmond:
Microsoft Press, 2008.
Plan for redundancy (Office SharePoint Server). Microsoft TechNet. [Online] July 15, 2008. [Cited:
September 22, 2008.] http://technet.microsoft.com/en-us/library/cc263044.aspx.
Plan for availability (Office SharePoint Server). Microsoft TechNet. [Online] September 5, 2008.
[Cited: September 22, 2008.] http://technet.microsoft.com/en-us/library/cc748824.aspx.