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jberryman
Asked: 2011-10-11 07:28:58 +0800 CST

Reliably and quickly migrate data to a RAID array

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We have a web service running on Amazon EC2. Currently we have some live user data stored on a single disk (EBS). We are considering moving to a RAID0 setup (we don't have to be concerned about the increased failure rate).

If we do this migration, what is the quickest (to minimize site unavailability) way to reliably transfer the user data to the RAID array?

One idea I had was to take a recent snapshot of the data, copy it over to the new RAID array, then when the site goes down for maintenance use rsync to copy only the changed data over. I'm not sure if this would actually save time or ensure data integrity though.

amazon-ec2

1 Answers

  1. Best Answer

    I use the exact approach you describe for migrating / copying data on EC2:

    1. Create EBS snapshot
    2. Create volume from EBS snapshot
    3. Warm up EBS volume (e.g., dd device to /dev/null)
    4. rsync
    5. Take production to maintenance mode
    6. rsync again
    7. Switch to new copy
    8. Bring production live again

    With the right options, rsync should ensure a close to exact copy from the file system level. It varies a little with Linux distro, but perhaps:

    rsync -aSHAX --delete source/ dest/

    The cool thing about EC2 is that you can test your entire migration plan on temporary volumes and temporary instances before you do it for real.

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