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Chapter 26: Log Shipping
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expected RTO is, that way in the case of disaster there is an established expectation for
getting data systems accessible again. This agreement is typically formalized in the form
of a service level agreement (SLA), which is a written agreement between the business and
technical units.Warm Standby Availability
Warm standby refers to a database that has a copy set up on separate hardware. A warm
standby solution can be achieved with log shipping. Log shipping involves periodically
restoring a transaction log backup from the primary server to a warm standby server, mak-
ing that server ready to recover at a moment’s notice. In case of a failure, the warm standby
server and the most recent transaction-log backups are ready to go. Apart from this, log
shipping has the following benefi ts:■ (^) It can be implemented without exotic hardware and may be signifi cantly cheaper.
■ It has been used for many years and is a robust and reliable technology.
■ (^) It can be used for disaster recovery, high availability and reporting scenarios.
■ Implementing log shipping is simple because Microsoft has a user-friendly wizard,
and when implemented it is easy to maintain and troubleshoot.
■ The primary server and the warm standby server do not have to be in the same
domain or same subnet. As long as they can talk to each other, log shipping works.
■ There is no real distance limitation between the primary and warm standby serv-
ers, and log shipping can be done over the Internet.
■ Log shipping allows shipping the transaction log from one primary server to mul-
tiple warm standby servers. It also allows having different copy and restore times
for each warm standby server. This can be useful to set up one secondary server as
a standby for disaster recovery purposes and use another secondary for reporting
purposes.
■ (^) Log shipping can be implemented between different editions of SQL Server
(Enterprise Edition to Standard Edition) and between different hardware platforms
(x86 or x64-based SQL Server instance; if you’re using an older version of SQL
Server, IA64 also applies).
However, log shipping has a few drawbacks:
■ Only user databases in full or bulk-logged recovery model can be log shipped. A
simple recovery model cannot be used because it does not allow transaction log
backup. This also means that log shipping can break if the recovery model for a log
shipping database is changed from full/bulk-logged to a simple recovery model.
■ System databases (master, model, msdb, and tempdb) cannot be log shipped.
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