Elastic Block Store (EBS) Architecture

EBS Basic Concepts

EBS is a service which provides block storage → raw disk allocations (volume)
- Volumes can be used by EC2 instances and other services
Volumes can be encrypted using KMS (or be left unencrypted)
EC2 instances see attached volume as a block device and can create a FS on top of this device (ext3/4, xfs, NTFS…)
‼️ Storage provisioned in ONE AZ
- Built-in resilience in the AZ, but AZ failure → volume failure
- ❗ Cross AZ attachments are not possible!
Volumes generally attached to one EC2 instance (or other service) over a storage NW
- Some volumes can be multi-attached to several instances (clusters), but generally not the case → cluster app must handle simultaneous data writes to prevent data corruption
Volumes can be detached and reattached (to same or different instance)
- Volume not lifecycle linked to one instance → Volumes are persistent
- Volume can follow instance when moving to a new host
Snapshot (backup) of a volume can be created in S3
- Volume can be created from S3 snapshot → migration between AZs possible
- Backups are regionally resilient (like S3)
- If global resiliency is desired → replicate S3 bucket across regions
Volumes come in different physical storage types, sizes & performance profiles
Billed based on GB/month (and in some cases performance)
- Single 2GB volume = Two volumes of 1GB = Four volumes of 0.5GB

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