EC2 Instance Storage

Memory hook: Choose block, file or local scratch first, then check its failure boundary, performance and recovery behavior.

Must remember

EBS and instance store

• EBS is persistent block storage in one AZ. The attached EC2 instance must be in the same AZ. It can outlive an instance, but delete-on-termination settings determine each volume's lifecycle.
• Root/data volumes can have different deletion behavior. Stopped instances and unattached EBS volumes can retain storage charges.
• gp3 separates capacity from configurable IOPS/throughput and suits general workloads. gp2 performance depends on size and burst behavior. More GiB is not always the best way to solve an I/O bottleneck.
• io1/io2 Provisioned IOPS SSD suits demanding transactional random I/O and predictable performance. st1 and sc1 HDD target sequential throughput and colder sequential data; they are not boot-volume choices.
• Volume and instance EBS limits both constrain performance; more provisioned IOPS cannot bypass instance bandwidth.
• Multi-Attach is supported for eligible io1/io2 volumes and compatible Nitro instances in the same AZ, with engine/OS/Region restrictions. It is not supported for gp3 or as a boot-volume shortcut.
• Concurrent block writes require a cluster-aware filesystem/application and correct coordination/fencing. Ordinary filesystems mounted read-write from unrelated servers can corrupt data.
• Instance store is host-local and ephemeral on host loss, stop or termination, unlike reboot. Use it for reconstructable cache, scratch or replicated data, never the only durable copy.

Snapshots, images and encryption

• Standard EBS snapshots store incremental changed blocks. AWS manages dependencies, preserving later snapshots' restorability when older snapshots are deleted.
• Restore a snapshot into a new volume to change AZ; copy snapshots for cross-Region recovery.
• An EBS-backed AMI adds boot/launch metadata and references image snapshots. Deregistering the AMI and deleting snapshots are distinct cleanup decisions.
• Snapshot-created volumes can require initialization for full performance. Fast Snapshot Restore removes that initialization penalty for enabled snapshot/AZ combinations, with additional charges. It does not make the data newer.
• Snapshot Archive converts an incremental snapshot into a full archived snapshot. It trades lower long-term storage rates for retrieval delay, retrieval costs and a minimum storage duration; it is poor short-lived lab storage.
• Recycle Bin retains eligible deleted snapshots/AMIs for recovery, delaying final deletion and potentially retaining charges.
• KMS encryption covers EBS data and associated snapshots. Copying an unencrypted snapshot into an encrypted one supports migration; an existing unencrypted volume does not simply gain in-place encryption.
• Sharing an encrypted snapshot requires appropriate snapshot permissions and access to a suitable customer-managed KMS key. AWS-managed default keys cannot be shared as though they were your own cross-account keys.

EFS: files instead of blocks

• EFS is managed NFS for concurrent Linux filesystem access. Regional EFS distributes storage across AZs; One Zone has a different failure boundary.
• Mount targets provide network access in VPC subnets. NFS reachability, security groups, file permissions and any configured IAM access controls all matter.
• Elastic throughput adapts to demand; Provisioned throughput sets a chosen throughput level; Bursting links available throughput/credits to the storage workload. These are distinct from storage classes.
• Standard, IA and Archive classify data by access/storage economics. Lifecycle policies can move cold files; retrieval and minimum-duration charges can outweigh savings for short retention.
• EFS fits shared uploads/home directories, not every block-database workload; storage integrations covers specialized Windows/HPC filesystems.

Choose under exam pressure

Traps

• Multi-Attach is not managed shared NFS. Shared blocks still require write coordination and remain in one AZ.
• A copy is only as current as its recovery point. More snapshots or faster initialization does not inherently improve the latest available RPO.
• Deleting compute is incomplete cleanup. Volumes, snapshots, AMIs, retention policies and filesystem data each have separate lifecycles.

Active recall

Terraform anchor: Trace volume, attachment, instance and snapshot dependencies; distinguish in-place changes from replacement and retained artifacts.

Sources

• EBS volumes.
• Multi-Attach.
• Snapshot Archive.
• Amazon EFS.
• EFS storage classes.