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Microsoft SQL 2000 Disaster Recovery with SANRAD V-Switch - Planning Guide
Designing a disaster recovery system requires planning and
consideration of the available options that will best fit your
company's needs, SLA and budget. With SANRAD DR Solution there
is no need to use Log shipping (which requires extra recovery
steps) or Microsoft SQL's built in replication mechanism (which
requires the configuration of a publisher and a subscriber).
SANRAD DR makes the data and transaction log available to the
SQL server on the remote site for immediate use. Even if there
is no SQL server on the remote site, once built after a
disaster, it will be able to access the data immediately with
minimum recover time. SANRAD DR solution is a "hot standby
solution" when there is a server on the remote site and a "warm
standby solution" when there is no SQL server on the remote site
(which will be built after a disaster). This guide will help you
design Disaster Recovery plan for Microsoft SQL 2000 in
conjunction with . The guide assumes that you have basic
knowledge of SANRAD V-Switch and MSSQL 2000 Administration.
Disaster Recovery Planning For Microsoft SQL 2000 This
section discusses both general and MSSQL specific considerations
that need to be addressed when designing a disaster recovery
solution combining and Microsoft SQL 2000.
General Considerations
solution allows for flexibility with Microsoft SQL 2000 disaster recovery design. The most
influential factors affecting design consideration are:
* Budget limitations
* Recovery Time Objective (RTO) requirements (the time until the
data is back online)
* Recovery Point Objective (RPO) requirements (the amount of
data that can be lost)
* Network bandwidth between the local site and remote site
* Replication method: Synchronous versus Asynchronous
* Replication frequency (only for Asynchronous replication)
* Initial volume synchronization
RTO (Recovery Time Objective)
* With high level RTO, duplicate hardware is required to allow
quick recovery making the solution more costly.
RPO (Recovery Point Objective)
RPO requirements are best defined by the amount of data that the
company is willing to lose.
* High level RPO requires more bandwidth for both Synchronous
and Asynchronous replication.
* Low level RPO requires less frequent replication and smaller
bandwidth.
Network Bandwidth between the Local and Remote sites
Bandwidth between the sites is generally the most crucial factor
affecting the replication component of a solution.
* T1 (1.5Mb) links impose less frequent data replication and the
use of asynchronous replication methods.
* T3 (45Mb) links or a 1Gb links allow frequent replication and
the flexibility to choose between synchronous replication or
asynchronous replication methods.
Replication method
When considering which replication method to choose it is
important to remember:
* In Synchronous Replication the I/O commands are written to the
local disk and to the remote volume at the same time. Every IO
command requires an acknowledgment from both the local
and
remote sites before the next command. Consequently, synchronous
replication is best deployed with a high bandwidth connection in
order to allow the remote acknowledgment to arrive back to the
local site as fast as possible and the replication can run
faster.
* In Asynchronous Replication the I/O commands are written to
the local volume and local journal volume which in turn is
replicated periodically to the remote volume as periodically
defined by the user. Consequently asynchronous replication can
work well with lower bandwidth (minimum recommended for
Microsoft SQL 2000 replication is 1.5 Mb).
* For Asynchronous replication, you must decide the data
replication frequency. There are three factors that must be
considered:
1. The size of the network bandwidth between the sites.
2. The amount of data changes that need to replicate each time.
For example, large amounts of data changes take longer to
replicate using T1 links.
3. The RPO requirements.
Initial Volume Synchronization solution can be used to
protect existing production Microsoft SQL 2000 data. solution
supports both online and offline synchronization. When using
with existing Microsoft SQL 2000 data, an Initial
synchronization of the Microsoft SQL 2000 volumes on the local
site to the remote site must be performed. The initial volume
sync method depends on:
* The size of the volumes needed to be synchronized.
* The network bandwidth between the sites. For example, the
bigger the volume size, the longer it will take to synchronize
over a T1 link.
Online synchronization starts immediately when
replication is started and uses the same network link that will
be used during the replication.
Offline synchronization is a manual process where
prepares the volumes on the primary site and the user must copy
the data to the remote site. It is the user's responsibility to
make sure the volumes on the remote site are synchronized.
Microsoft SQL 2000 Considerations
Any Microsoft SQL 2000 Disaster Recovery planning should
(at the very least) consider the following requirements:
* Quick access to the most recent copy of the Microsoft SQL 2000
database and the transaction logs. In a disaster situation
provides fast access to the most recent replicated data on the
remote site.
* The Microsoft SQL 2000 database and its related transaction
logs must be replicated together to the remote site. uses
consistency groups to ensure simultaneous replication of all
volumes assigned to a consistency group.
This article deals with designing a disaster recovery system
while planning and considering the available options. It further
discusses about suggested Disaster Recovery Designs, fully
Mirrored Remote Site, partially Mirrored Remote Site, small
Remote Site, combining SANRAD Disaster Recovery Designs with
Microsoft SQL 2000 Disaster Restore Models, restore Microsoft
SQL 2000 with a Standby Server and restore by Rebuilding
Microsoft SQL 2000 Server. For further reading click here
About the author:
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