Data Migration is the process of transferring data between different storage types, servers or formats. It’s not just about copying data, but also about validating the data according to constraints and since different databases uses different data types, this step also include modifying the data as per the target server. One essential requirement is that the data migrated should verify the Business logic to run applications smoothly on target server.
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Migrating from one server to another can be a tricky situation. There are various challenges while migration of full data from UNIX server to Microsoft Server. First of all the user should completely understand the data sources and their proper formats. Usually, too many spreadsheets or excel files, or redundant data may affect proper migration. Wherever possible, instead of manual, automated systems should be used. Microsoft offers MAP (Microsoft Assessment and Planning) tool to identify the various constraints, or issues that might occur while migrating from UNIX platform to Microsoft server. Moreover, SSMA (SQL Server Migration Assistant) can further help in performing the migration. SSMA can create mapped schemas to UNIX server, which helps in easy migration of data.
It is essential that the all applications like email, finance systems, personal records, CAD/CAM engineering facilities, production systems, Sales & Marketing databases, Website etc. should run smoothly after migration. There are various underlying steps that need to be taken care of for easy and error-free migration, as explained below:
- Recognizing the pattern-Template Creation: To begin migration, first we’ll have to understand the schema of UNIX database. We’ll create a template consisting of master data key objects. The template has following two sections:
Section 1: Key Data Fields: In the first section of the template user will provide the key values, such as storage objects material, address etc. Usually, in key field columns, drop-down lists are provided for accurate and easy entry of data.
Section 2: Derived and Default Fields:Based on the key field values, various fields can be derived based on the Business translational logic. For example, using the production unit key field the template will determine the employee names working in it. For different production units, different employee names will be automatically derived by the template.
The default fields like, “currency used” will be automatically updated.
- Process of Migration: The process of migration is summarized on the figure below:
Figure-1 (Source: Ranga Rao Davala, Nikhil Singh, 2011, A Case Study on Data Migration Strategy, The Data Administration Newsletter, Robert Seiner Publishers.)
- Select Source:Due to various applications running on UNIX server, the data will be spread across many sources like different DBs, excel files or spreadsheets. In this step, user will identify the various data sources that are to be migrated. The selection of sources will be based upon the requirements in the project, according to which what data needs to be migrated can be identified.
- Data Fields Mapping:This is an essential step, where the schema or key fields from source system are mapped to target system. The field names in target schemas should be kept similar to source schema for easy mapping. This step is usually done manually for error-free mapping. Usually the different database servers will have different underlying data types. For example, Integer’s maximum and minimum limit in UNIX server is different from in SQL Server. The mapped data, therefore, should be transformed according to destination server data types.
- Data Transformation:This is where the template we created will come in picture. User will manually enter the key field values in the template and based on that all the derived and default field values will be generated automatically. Moreover, in this step, the user will transform the data based on the difference between data types of both servers.
- Validations and Constraints:This step is to ensure that the data entered in the template is accurate. The template will gray out the field which are entered wrong or doesn’t qualify the constraints, such as mandatory fields, null values etc. This step will help in minimizing errors and improving the quality of data.
- Extract Files:Once the data is entered into the template, the master data objects are extracted or generated.
- Load files:The load files are in text format, and they can be generated in single click by macro-enabled extract files system. This step ensures that data present in the text file is in exactly the same format as we require in the Microsoft system.
- Loading data in Microsoft Server:The data is loaded in batches. Since there are multiple applications running on UNIX system that are to be migrated, this step may take several hours to complete.
Web server migration (FTP or HTTP Websites)
Once we have completed the initial steps of creating a template and selecting the proper migration tools, we can begin full migration from UNIX to Microsoft server i.e. IIS. We must follow following steps:
- Assessment of hardware requirements and acquiring new hardware if required.
- We can begin migrating FTP or HTTP websites by copying their content to destination server.
- Next step is to replicate Web application files to destination.
- Migration of log files.
- Migration of Web server configuration settings.
- The last step is to create security settings and user permission and roles.
DHCP/DNS Migration:
The process of migrating UNIX server DHCP/DNS services to Microsoft Windows Server DHCP/DNS servers requires the following steps:
- Install Microsoft Windows Server DHCP/DNS Services Manually
- Configure Microsoft Windows Server DHCP/DNS Services
- Create Forward and Reverse Lookup Zones: Creating lookup zones will make sure that Microsoft server is authoritative for the DHCP/DNS names for local resources and forwards other queries to an ISP or performs recursive resolutions.
- Add secondary zones to Microsoft Windows Server DHCP/DNS for the existing zones that are hosted on UNIX based DHCP/DNS servers.
- In this step we’ll initiate zone transfers at the Microsoft Windows Server-based DHCP/DNS servers to transfer the zones from the UNIX servers.
- After the transfers are successful we will convert secondary zones into primary zones.
- In the last step, we’ll point client configurations to Microsoft Windows based DHCP/DNS Servers.
Avoiding downtime while migrating:
We can avoid the downtime while migration by reconfiguring our sites to connect to our new database remotely. Using this way, our users or visitors will be redirected to new site and all the updates will be saved to new server. This technique is, though, very complex, but it will minimize the downtime to a great extent. We can summarise this process in following steps:
- Transfer the files, DBs and important settings to the new server.
- Then we can test our site on the new server to check if it’s working as expected.
- After two steps are successfully completed, we will change the various database settings on our site, to make sure that the old server accesses the DB from the new server.
- Then we’ll modify the name servers and DNS and point them to the new server.
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