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On EC2, most of the larger current generation instances have multiple SSD devices. To take advantage of the combined size of these for applications like nosql databases that store large amounts of data, I've been combining them with software raid 0 or 10 using mdadm.

It takes forever when launching new instances though, for instance to run the initial raid10 sync on an i2.4xlarge instance takes several hours to complete.

Is there any way to speed this up? Is it possible to save an AMI after running the initial mdadm sync that will include all the ephemeral disks in the same raid configuration when it lauches?

I haven't used custom AMI's much but from reading the docs it sounds like both instance store backed and ebs backed AMI's only include a snapshot of the root volume.

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closed as off-topic by Frands Hansen, mdpc, MadHatter, Nathan C, Ward May 10 at 17:13

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1 Answer 1

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As you've noticed, ephemeral disks are not included in an AMI snapshot; only the root volume is. Because of this it's not possible to "snapshot" the metadata of mdadm because the ephemeral disks will be lost when the instance hosting it is destroyed. You can however create persistent RAIDs with EBS volumes.

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Thanks, good to confirm I wasn't just missing something. –  danny May 12 at 15:15

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