Correct way to take a snapshot

Question

I've asked this question before, but I am still confused. What's the correct and quickest way to take a snapshot (I only use EBS-backed Unix and Windows machines, so that's all my interest right now). Some ideas:

• Just take the snapshot... This seems to sometimes cause system corruption.
• Stop the machine, take the snapshot and then start the machine. I guess this also means I need to wait for each individual task to complete, making scirpting a bit of a challenge?
• Take a snapshot with the 'reboot machine' flag set. There is very little in the documentation to specify why a reboot is needed...

Hope you EC2 experts can help me.

Answer 1

If a bit of data loss is acceptable, just take the snapshot while the instance is running. If it's not acceptable, write some script magic to ensure everything your application is working on is saved to disk, take the snapshot, then let your app resume work.

For what I do, I find it best to keep a separate EBS volume with my application and its data on it, and when I need a snapshot, I just stop the app for a moment, snapshot, and fire it back up. That way you don't have to worry about what the OS is doing during the snapshot, and it also comes with the added bonuses of being able to quickly move your app and its data to more powerful hardware, and having much smaller snapshots.

Answer 2

Taking a snapshot often requires scheduled downtime.

Procedure:

1. I'd unmount the drive.
2. Start the snapshot and wait until it's done.
3. And then re-mount it.

Afaik, the only viable way for a consistent snapshot.

If you could share more about what kind of data is on the snapshot (e.g. a database?), then I could probably extend my answer.

I cannot comment on Windows-based instances since I'm not at all familiar with it but in order to avoid redundancy, check out this blog entry explains as it explains a lot:

• http://shlomoswidler.com/2010/01/creating-consistent-snapshots-of-live.html

In a nutshell, they use the xfs file system and when they freeze it to create the snapshot, they allow updates to the filesystem to pass. According to the comments, it seems to work for most people.