Data Persistence

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Exam Tips:
- Ephemeral
  - Data this is local to a resource (usually) and lost when the resource is powered off.
    - Instance Store Volume
      - Attached to host in an AZ, failure of either host or AZ means failure of the volume.
    - Amazon ElastiCache
  - Very high throughput.
  - Data is lost when the resource is powered down.
  - Data does survive a reboot, but if an instance is terminated or the disk itself fails, the data is lost.
- Persistent
  - Data that is durable and able to survive power events such as start, stop, and restart.
    - Amazon EBS (Elastic Block Store)
      - Replicates within an AZ.
      - Failure of AZ means failure of a volume.
      - Can store snapshots in S3 which is regionally resilient, and then copy the snapshots to S3 buckets in other regions.
    - Amazon EFS (Elastic File Store)
      - Replicated across multiple AZs- By default regionally resilient.
      - Failure of the region means failure of the filesystem.
  - Comes at an extra cost.
  - Not default.
  - Good for things such as databases.
- Transient
  - Datastores that exist with the intention that the data injected is temporary.
    - SQS
  - Not used for permanent storage.
  - Used as intermediaries between services.