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Restoring an Amazon EBS RAID0 array from snapshots taken with ec2-consistent-snapshot
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I've configured a new MySQL server on Amazon EC2 and decided to store my data on a EBS RAID0 Array. So far so good, and I've tested taking snapshots of those devices with ec2-consistent-snapshot, great. Now, how do you rebuild the array on a new instance, from these snapshots, quickly? When you use ec2-consistent-snapshot to create a snapshot of multiple volumes, you have no way to tell which volume was used for each device in the RAID. I maybe completely wrong, but since you're striping data across the volumes, it would stand to reason that you have to put each NEW volume in the same location on the RAID as the volume from which the snapshot was created. An example:
you create an ec2 snapshot with: You now have 3 snapshots, and the only way to trace back which device they are is to look at the source volume id, then look at which device the source volume id is mounted as on the instance, and then check the details of the RAID configuration on the source volume's instance. This is obviously incredibly manual...and not fast (which obviously makes it hard to bring up a new mysql instance quickly if the other one fails. not to mention, you'd have to record the device positions on the RAID at the time of snapshot, because if the source volume instance crashes, you have no way to get to the RAID configuration). So, in conclusion:
I hope this was clear, and thanks for your help!
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2 Answers
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I know this doesn't answer your question, but I'm doing something similar but with Amazon's base ec2-create-snapshot tool and a cron script. It's not as fast as ec2-consistent-snapshot, but I get the extra control I need: fsync, lock writes, and most importantly, name the snapshots appropriately so they can be reconstituted in the correct order. |
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I tested your premise, and logical as it may seem, the observation is otherwise. Let me detail this: I'm using Ubuntu 10 and have 2 EBS devices forming a RAID0 device formatted with XFS. The raid0 device was creating using the following command: I've installed MYSQL and a bunch of other software that are configured to use /dev/md0 to store their data files. Using the same volumes: Once done, I umount everything, stop the Raid and reassemble it like so: Using snapshots: Post this, I use Sounds strange, but it works. |
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February 7, 2011
February 7, 2011