CloudWatch Metric Guide
FreeStorageSpaceAmazon RDS CloudWatch metric
FreeStorageSpace reports the available storage capacity on the RDS instance's EBS volume, in bytes. When this reaches zero, the database stops accepting writes.
What it measures
About FreeStorageSpace
FreeStorageSpace reports the available storage capacity on the RDS instance's EBS volume, in bytes. When this reaches zero, the database stops accepting writes.
| Namespace | AWS/RDS |
| Metric name | FreeStorageSpace |
| Unit | Bytes |
| AWS docs | Official Amazon RDS metrics reference |
Why this metric matters
Disk-full is one of the few RDS failure modes with no graceful degradation — the moment FreeStorageSpace reaches zero, all write operations fail immediately. For MySQL and PostgreSQL, this means transaction rollbacks, connection errors, and an instance that appears healthy from a CPU and memory perspective but refuses all data modifications.
The failure mode is particularly treacherous because storage consumption is usually gradual and predictable — logs accumulate, WAL segments grow, temp files aren't cleaned up. These are all preventable with visibility. The fix (storage auto-scaling or manual resize) takes minutes once you know it's needed, but costs hours if you're diagnosing from incident tickets.
Recommended alarm threshold for FreeStorageSpace
Recommended threshold
< 20% of total allocated storage, or < 5 GB absolute floor (whichever is larger)
AWS documentation recommends enabling Storage Auto Scaling as a preventive control, but even with auto-scaling, alarms are essential for tracking consumption trends. The 20% floor (Nuberio recommendation) is sized to give enough runway for storage auto-scaling to provision additional capacity — the resize window can take several minutes for large volumes.
Is your FreeStorageSpace alarm already set up correctly?
The free Nuberio Audit scans your CloudWatch setup and flags missing or misconfigured alarms — including FreeStorageSpace — in 5 minutes.
Common failures that show up in FreeStorageSpace
When FreeStorageSpace reaches an alarm threshold, these are the most common root causes — in order of how often Nuberio sees them across customer AWS accounts.
Binary log accumulation on MySQL — replication logs not purged, consuming hundreds of GB over weeks
Write-intensive workload with storage auto-scaling disabled — no alarm means no action until writes fail
Temporary file explosion — complex queries or bulk exports creating large temp files that aren't automatically cleaned
WAL segment accumulation on PostgreSQL — archive_cleanup_command not configured or stalled replication slot holding old WAL
Forgotten test or migration data — large tables from a data migration never dropped after the migration completed
How the Nuberio Audit checks FreeStorageSpace
The free Audit scans every Amazon RDS resource in your account and checks whether a FreeStorageSpace alarm exists, whether its threshold and evaluation period are configured sensibly, and flags it if it's missing entirely. Every finding comes with the exact CLI command to fix it — read-only access, no credit card, results in about 5 minutes.
Nuberio Audit
Scans your CloudWatch setup for missing or misconfigured FreeStorageSpace alarms. Free, 5-minute read-only scan.
Related Amazon RDS metrics
FreeStorageSpace rarely fails in isolation. These metrics tend to correlate — monitor them together for complete Amazon RDS coverage.
FAQ
Frequently asked questions about FreeStorageSpace
Common questions about setting up CloudWatch alarms for FreeStorageSpace in Amazon RDS.
What is the recommended CloudWatch alarm threshold for FreeStorageSpace?+
< 20% of total allocated storage, or < 5 GB absolute floor (whichever is larger). AWS documentation recommends enabling Storage Auto Scaling as a preventive control, but even with auto-scaling, alarms are essential for tracking consumption trends. The 20% floor (Nuberio recommendation) is sized to give enough runway for storage auto-scaling to provision additional capacity — the resize window can take several minutes for large volumes.
Which CloudWatch namespace does FreeStorageSpace belong to?+
FreeStorageSpace is published in the AWS/RDS namespace with a unit of Bytes. You can find it in the CloudWatch console under "Metrics" → "AWS/RDS". See the Amazon RDS CloudWatch metrics reference in the AWS documentation.
Does Nuberio automatically create CloudWatch alarms for FreeStorageSpace?+
No — the free Nuberio Audit does not create alarms for you. It scans your CloudWatch setup and tells you which Amazon RDS resources are missing a FreeStorageSpace alarm, then gives you the exact CLI command to create it yourself.
Can I use Nuberio without already having a FreeStorageSpace alarm set up?+
Yes. The free Audit works whether or not you have any FreeStorageSpace alarm configured — it reads the resource directly from CloudWatch and tells you which resources need one, plus the copy-paste AWS CLI command to create it.
This page is part of the CloudWatch metric guide — thresholds and debugging guidance for every metric across RDS, Lambda, ECS, ALB, EC2, DynamoDB, SQS, API Gateway, S3, CloudFront, ElastiCache, and EKS. To find which Amazon RDS alarms your account is missing — including FreeStorageSpace — run the free CloudWatch alarm audit. The scan takes under 5 minutes and requires no account.