EC2 Instances primarily utilize storage known as EBS Volumes. But this isn’t the only type of storage that is available. There’s another type, known as Instance Store, or Ephemeral Storage.
Instance Store was first used by Amazon, until they shifted to Elastic Block Store. There are several differences between EBS and Ephemeral Storage that may be worth understanding for us as Cloud Engineers.
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The AWS Documentation mentions that Amazon Instance Store is designed for temporary storage for EC2. Things like Buffer, Cache,, in Raid Arrays, or Temporary Backups. are some possible use cases for instance store.
I was surprised to see this storage option besides EBS, because EBS is the default. EBS is is the DeFacto standard when launching an EC2 instance.
It’s actually pretty tricky to figure out where you can actually use ephemeral storage when launching EC2 instances. For example, if you try to launch a t2.micro EC2, or even most of the other instance types, you will not be able to attach ephemeral storage.
But if you launch the m3.medium EC2, then you are able to add ONE instance store. And for the g2.8xlarge, it allows you to add TWO additional instance stores. And if you create a new AMI image from a launched EC2 instance, then you can attach as many Instance store volumes as are available (24 total).
Don’t ask me why it’s all set up this way. I’m clueless. But If you do know, please explain it by leaving a comment below.
I don’t expect you to fully understand Ephemeral Storage just by this post, but hopefully this helped to clarify a bit the concept of Ephemeral Storage according to AWS. Like is the case with most of AWS, after getting the theory, you gotta “get your hands dirty” by playing around in the actual AWS console.