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Data migrations can be complicated, time consuming and happen all too frequently. Here's how to simplify the process.|
whatever storage media your data sat on a year or two ago, chances are it's moved since then and will likely move again soon. There are plenty of reasons why that data may have to move: maybe the lease is up on an old Fibre Channel (FC) SAN and you're upgrading to new hardware, you're moving to a new data center or you need to move older files to less expensive storage to keep up with soaring data demands.
Data migration may be a common chore, but that doesn't mean it's easy. Disk (and tape) drives are linked to applications and business processes through servers, routers, switches, and storage and data networks, not to mention access control policies and other layers of security. The more complex your environment, and the more data you're managing, the less likely you'll be able to use simple copy functions built into operating systems or arrays to pull off your required migrations.
Migrating data involves a lot more than just ripping out one storage cabinet and plugging in another. The following tips will help make your data migrations go more smoothly.
before migrating any data to new storage arrays, be sure you understand how servers are currently mapped to storage so you can re-create those mappings in the new environment. Otherwise, servers may not reboot correctly after the migration.
To avoid unplanned outages, administrators should "understand the true end-to-end relationships among the platforms you're moving across," says Lou Berger, senior director of products and applied technologies at EMC Corp. This is especially important if, for redundancy purposes, your storage infrastructure is a multipathing environment where hosts may boot from alternate arrays if the primary array is down. If administrators fail to check the parameters on the host HBAs to ensure the pathing software is set up correctly, he says, the host may not reboot properly.
Administrators also need to be sure the host will discover storage resources in the proper order after a migration. "Some applications and databases are sensitive to the order in which they discover volumes," says Berger, because an application boot sequence might be on one LUN and its data on another.
Administrators may not even know a server exists until it fails to reboot after a migration, "because oftentimes people install them and forget them," says Ashish Nadkarni, a principal consultant at GlassHouse Technologies Inc., a Framingham, MA-based consulting and services firm. While storage discovery and auditing tools are valuable, he says, none of them can capture 100% of the misconfigurations that can cause a problem.
This was first published in November 2008