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Amazon permits you to image a hot volume -- one that is online and running. Does this come at a cost to image-speeds though? Will it image the volume substantially faster if you take the instance offline?

Evan Carroll
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1 Answers1

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AMI creation uses EBS snapshots, which are instantaneous, point-in-time snapshots of the volume, so no: imaging a "live" volume will not be any slower or faster than imaging an offline vol.

However, imaging a live mounted volume means that it's a dirty copy of the filesystem, and will need to go through fsck on first boot, possibly losing data in the process. As such, it's recommended that you always stop instances before creating AMIs from them.

EEAA
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  • I've read that instantaneous point-in-time piece quite a bit, but this is not instantaneous. I've got a 500 GB EBS volume that has been churning away to generate an AMI image (instance stopped), and it's at 4% 30 minutes later. – Evan Carroll May 22 '13 at 03:52
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    Taking the snapshot **is** atomic. What takes time is building the image file, copying it off to S3, etc. Once you start the AMI creation process, you can start using the instance, as any future writes to those volumes will not be reflected in the snapshot. – EEAA May 22 '13 at 03:56
  • Wow, this I did not know. So I can stop the instance, do a snap shot, and start it up (before completion) and and the snap shot will continue without being "dirty"? – Evan Carroll May 22 '13 at 03:58
  • Yes, that's correct. – EEAA May 22 '13 at 03:58