Pre-migration. Migration prep consists of detailed activities to ready the server, network and storage systems impacted by a given migration. Activities include:
- Backing up data
- Capturing current configuration information
- Detailed review of all planned changes at each level
- Identification of migration validation checkpoints
- Script configuration and review (if used)
- Review/verification of LUN/volume source and target information
- Review/verification of pre- and post-migration OS-level drive mappings
- Review/verification of post-migration app reconfiguration
- Review/verification of clustering modifications
- SAN reconfiguration and rezoning
- Storage preparation
- Host preparation (dependent on migration approach)
Migration. Data migration can be accomplished at several levels. The selection depends on the number of servers and storage devices, the quantity of data, the distance involved and the tolerable level of impact to apps.
Host-based: The traditional means of migration, pre-dating storage networking, is host-based. Approaches include app-specific migration, database replication, the use of OS-based or third-party volume managers to mirror and split volumes, general OS file-copy utilities and special-purpose migration apps. Each has its particular advantages and disadvantages. The overall benefit of host-based replication is that it can support heterogeneous storage and be economical for smaller scale requirements. General disadvantages are the intrusiveness and impact on the host, and overall scalability when lots of systems are migrated.
Storage-based: Migrating at the array reduces host impact, but has traditionally been limited to homogeneous transfers, such as moving between generations of a vendor's product line--a reasonable option if you happen to fit this scenario, but a non-starter if you don't.
More recently, the situation has changed. Specifically, Hitachi Data Systems' (HDS) TagmaStore controller-based virtualization product can support a variety of non-HDS arrays making it an excellent option for migrating data. EMC offers its Open Replicator for Symmetrix, a resident utility that can pull or push data to non-Symmetrix systems on a SAN thereby enabling "outside-the-box" data movement.
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