Inactive and Unmounted EFS File System

Shireen Maini

Service Category

Storage

Cloud Provider

AWS

Service Name

AWS EFS

Inefficiency Type

Unused Resource

Explanation

EFS file systems that are no longer attached to any running services — such as EC2 instances or Lambda functions — continue to incur storage charges. This often occurs after workloads are decommissioned but the file system is left behind. A quick indicator of this state is when the EFS file system has no mount targets configured. Without active usage or connection, these orphaned file systems represent pure cost with no functional value. Unlike block storage, EFS does not require an attached instance to incur billing, making it easy for unused resources to go unnoticed.

Relevant Billing Model

EFS is billed based on:

Total data stored (per GB/month)
Storage tier (Standard or Infrequent Access, if lifecycle policies are enabled)
Optional provisioned throughput (if configured)

Even when unmounted, EFS continues to accrue storage cost until deleted.

Detection

Identify EFS file systems with no mount targets present
Check for file systems with no recent read/write activity over a representative time window
Correlate with decommissioned EC2 instances or workloads that previously used the file system
Confirm with workload owners whether the data is still required or can be deleted

Remediation

Delete EFS file systems that are no longer in use and have no attached mount targets
If data must be retained, consider exporting it to a lower-cost storage service (e.g., S3 Glacier) before deletion
Establish periodic audits to identify and clean up orphaned file systems

Relevant Documentation