Benefits of EBS vs. instance-store (and vice-versa)
I'm unclear as to what benefits I get from EBS vs. instance-store for my instances on Amazon EC2. If anything, it seems that EBS is way more useful (stop, start, persist + better speed) at relatively little difference in cost...? Also, is there any metric as to whether more people are using EBS now that it's available, considering it is still relatively new?
Answer
The bottom line is you should almost always use EBS backed instances.
Here's why
- EBS backed instances can be set so that they cannot be (accidentally) terminated through the API.
- EBS backed instances can be stopped when you're not using them and resumed when you need them again (like pausing a Virtual PC), at least with my usage patterns saving much more money than I spend on a few dozen GB of EBS storage.
- EBS backed instances don't lose their instance storage when they crash (not a requirement for all users, but makes recovery much faster)
- You can dynamically resize EBS instance storage.
- You can transfer the EBS instance storage to a brand new instance (useful if the hardware at Amazon you were running on gets flaky or dies, which does happen from time to time)
- It is faster to launch an EBS backed instance because the image does not have to be fetched from S3.
- If the hardware your EBS-backed instance is scheduled for maintenance, stopping and starting the instance automatically migrates to new hardware. I was also able to move an EBS-backed instance on failed hardware by force-stopping the instance and launching it again (your mileage may vary on failed hardware).
I'm a heavy user of Amazon and switched all of my instances to EBS backed storage as soon as the technology came out of beta. I've been very happy with the result.
EBS can still fail - not a silver bullet
Keep in mind that any piece of cloud-based infrastructure can fail at any time. Plan your infrastructure accordingly. While EBS-backed instances provide certain level of durability compared to ephemeral storage instances, they can and do fail. Have an AMI from which you can launch new instances as needed in any availability zone, back up your important data (e.g. databases), and if your budget allows it, run multiple instances of servers for load balancing and redundancy (ideally in multiple availability zones).
When Not To
At some points in time, it may be cheaper to achieve faster IO on Instance Store instances. There was a time when it was certainly true. Now there are many options for EBS storage, catering to many needs. The options and their pricing evolve constantly as technology changes. If you have a significant amount of instances that are truly disposable (they don't affect your business much if they just go away), do the math on cost vs. performance. EBS-backed instances can also die at any point in time, but my practical experience is that EBS is more durable.