Expanding a four-disk RAID array
I have a four-disk RAID 5 configuration that is running out of room. I currently have four 9.1 GB UltraSCSI-2 drives. Can I replace each drive, one at a time, with larger drives and have the array rebuilt to accommodate the larger drives? I have two volumes on the array. Can I expand the data volume to assume the increased space?

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Thank you for the question. This question has come up a number of times in my work and the answer all depends on what the RAID vendor supports. Unfortunately, there is no standard answer to what can be done and what can't in a generic RAID 5 configuration, as each RAID controller allows for different operating capabilities. Some will allow you to rebuild a RAID implementation on the fly and add disks as needed, while others will not, requiring you to back up the data, tear down the RAID configuration and rebuild it, and then restore the data back from tape or mirroring back using a host based volume manager. I would check with your RAID vendor and ask them what they support doing in this environment.

This was first published in October 2004