Ref: https://learn.cantrill.io/courses/1820301/lectures/41301324

• Summary
• Contents:

💡 Understanding pros & cons of instance store volumes can save money & improve performance, misunderstanding them can cause significant headaches

EC2 Instance Store - Characteristics

• 🔧 Highly-performant, ephemeral, local, block volumes
• Block storage devices
  • Raw volumes which can be attached to an instance
  • FS can be mounted on them
• Local
  • Physically connected to a single EC2 Host (NOT over NW)
  • Each host has its own instance volumes, which are isolated to that one particular host
  • Instances on host can access these volumes if configured to do so
• ❗ Included in instance price
  • Different instance types and sizes support different types and sizes of volumes
    • Some instances don't include instance store volumes at all
    • Larger instance size usually supports larger volumes
  • You pay for it anyway → use it or lose it
    • No advantage to not utilizing them
• ‼️ Attached at launch time! They can NOT be attached after launch time!!!
  • You can use provided volumes at launch or not, but you can't adjust this later unless you relaunch the instance!
• 👍 Best benefit: performance
  • Because they're local, they offer the highest performance available within AWS (much higher IOPS and throughput than what EBS can provide)
  • E.g. 1: D3 instance (storage optimized) → 4.6 GB/s throughput
    • large amounts of storage using traditional hard disks → really good value
    • much higher levels of throughput than maximum levels of EBS HDD-based volumes
  • E.g. 2: I3 instance (also storage optimized) → NVMe SSDs = 16 GB/s of sequential throughput
    • Some large I3s can provide IOPS in the millions when optimally configured
• 👎 Biggest limitation: ephemeral (temporary) nature
  • ❗ Do NOT use for data you rely on or irreplaceable data!
• Use cases: Buffers, caches, scratch data, replicated data (e.g. load-balanced pool of web servers)…

EC2 Instance Store - Architecture

• Each EC2 instance can have 0+ instance store volumes
• Volumes are backed by physical devices on the host
• Ephemeral volumes: ephemeral[0-23]
  • ❗ Storage can be lost if:
    • instance changes host
    • instance changes type or size → usually means changing hosts
    • HW failure (both entire host failure or HW-specific failure)
  • If you store a file on ephemeral0, then migrate instance to another host, you will still see ephemeral0… but the file won't be there!
    • 💡 ephemeral0 volume is different because it's in a different host!