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Special types of data migrations
A data migration doesn't always equate to moving data from one disk to another. While these may represent the bulk of data migrations, other types of migrations usually require even more forethought and can make a migration from one disk to another seem like child's play. If you attempt the following data migrations, make sure your back-out plan works and that you can recover to your existing environment.
Database

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Migrations. Migrating data from a SQL Server database to an Oracle database or vice versa requires that tables, indexes, primary and foreign keys, unique and check constraints and default values as well as security are all factored into the migration plan.
Directory service migrations. Migrating data from Novell's NDS to a Windows ADS or vice versa brings its own set of issues. User accounts and existing domains--along with the corresponding security settings on the objects in the existing environment--must be replicated to the new environment for everything to work. A product such as Bind View's bv-Admin Migration Solutions can help facilitate this sort of task.
E-mail migrations. Moving from one e-mail platform to another, or even upgrading the existing e-mail platform, can disrupt the entire enterprise. Address books, calendars and e-mail retention policies, as well as the messages and their message format, all need to be converted and migrated into the new environment.

Network-based tools such as FalconStor Software's IPStor and DataCore Software's SANsymphony offer a vendor-neutral approach from an operating system and storage perspective. Yet these approaches sometimes make administrators uneasy because of the time required to set up these roducts.

Before a network-based migration commences, an administrator needs to set up zones, allocate LUNs on the new arrays and reboot servers so they can discover the new volumes on the new array. The amount of risk that something will go wrong correlates to how large the networked storage environment is and how well it's maintained and documented. Poorly maintained and documented storage area networks (SANs) may require weeks--if not months--to identify, schedule and verify each server's access to volumes on existing arrays, and also verify their access to volumes on the new arrays after they have been allocated. Migrating data from one database format to another presents a set of additional problems (see "Special types of data migrations").

Host migrations
Host-based replication technologies exist for nearly every major operating system platform, including mainframe, Novell, Windows and most flavors of Unix. The free utilities that ship with the operating systems should only be used with offline applications or files. Look for a third-party solution if you need to maintain application availability while moving data to a new storage location. Products differ in the number of steps required to perform the data migration and how they manage the process.

There are a number of good reasons to use host-based technologies for data migrations such as:

  • Lack of money to purchase replication software
  • Inexperience with array- and network-based solutions
  • Comfort level with existing migration techniques
  • Integration with existing databases or a mix of different vendor's storage arrays
But before selecting a host-based tool, it's important to understand its pros and cons:

Pros:

  • Migrates from anything (internal or external disk) to anything
  • Inexpensive if used with existing OS utilities
  • Can change volume characteristics during migration
Cons:
  • Requires root-level access to each server
  • May need to install software in addition to migration software
  • Need to uninstall software following the migration
Administrators also need to consider if and how the utility handles periods of network latency. Not all data migrations will be from one array to another on a high-speed Fibre Channel (FC) network. As organizations consolidate data centers, data migrations will increasingly occur asynchronously over longer distances. So the utility must not only monitor the performance of the application on the server, but the speed of the migration. And the migration software must recover from interruptions that may occur during the data migration.

Tools such as Veritas' StorageCentral and Storage Reporter track data usage and profile storage resources--information essential for a successful data migration. Once the migration begins, Veritas' Storage Foundation analyzes the amount of disk space that will be saved and shows a progress bar as the data is migrated.

Look for products that monitor network traffic during data migrations, and in the event of a network slowdown, store all source changes and transmit them when possible. They should also perform resyncing operations to get the target data back in sync with the source data. And ensure the tools have a central management console from which to manage the migration.

This was first published in May 2004

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