Microsoft SQL 2000 Disaster Recovery with SANRAD V-Switch - Planning Guide
By Efrat Aharoni-Levi

Introduction

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.

SANRAD is a leader in IP Storage Networks enabling organizations to effectively Access, Share & Manage Stored Data across Standard Ethernet Environments.

SANRAD delivers simplified networked storage with excellent price/performance by coupling open IP storage connectivity with comprehensive network-based data management using IP Storage Area Networks (IP-SANs).

With SANRAD, organizations of all sizes can leverage the benefits of networked storage to link employees and clients with stored data for full storage availability, flexible and scalable storage using an economical Ethernet (IP/SCSI) network.

for further reading: http://www.sanrad.com/objects/support/Library

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