Ask the Expert:RAID rebuilds

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Q: I run four 400GB SATA drives configured with RAID 5. I want to replace them with four 750GB drives. Can I rebuild and then swap individual drives?


A: RAID rebuilds take quite a long time and are a resource-intensive operation, so expect your application to suffocate while this is happening. Rebuilds are a protection mechanism and aren't designed for data migration. Assuming your 750GB drives are sup-ported with your RAID adapter, the RAID group will only utilize the first 400GB of storage on each 750GB drive, leaving the remainder inaccessible.

The usual way to migrate data with internal server-based storage is to copy the data to a separate set of drives or temporary storage, install the new drives and then copy everything back, remembering to preserve all file attributes. A tool like Robocopy can do this.

--Ashley D'Costa, enterprise solutions architect, Mainland Information Systems Inc.

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This was first published in March 2008

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