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 (ConvOps 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 ConvOps 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 ConvOps 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 ConvOps debugs FreeStorageSpace alarms
When FreeStorageSpace triggers an alarm, ConvOps Diagnose reads CloudWatch Logs, CloudTrail (recent API calls, deploys, config changes), and the current resource state in parallel. It correlates these with AWS/RDS metrics on the same resource — giving you a plain-English root cause with numbered fix options, sent to WhatsApp or Slack, usually within 60 seconds of the alarm firing.
Before any anomaly in FreeStorageSpace reaches you as a proactive alert (via ConvOps Watch), it passes through 9 verification checks: a Recovery check (did the metric self-heal?), an AWS Status check (is AWS itself having an incident?), a Deploy check (was there a recent Lambda update, ECS deploy, or RDS parameter change in the last 120 minutes?), a Quota check, an Infrastructure check, a Security check, a Flap check (has this metric been anomalous more than 5 times in the last 24 hours?), a TLS check, and a Vulnerability check. Only anomalies that pass all relevant checks reach you — with full context attached.
ConvOps Watch
Detects FreeStorageSpace anomalies with z-score against 30-day time-bucketed baselines. 9 verification checks before any alert.
ConvOps Diagnose
When a FreeStorageSpace alarm fires, reads logs, CloudTrail, and resource state. Sends root cause + fix options to WhatsApp or Slack.
ConvOps 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 (ConvOps 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 ConvOps automatically create CloudWatch alarms for FreeStorageSpace?+
ConvOps does not create alarms for you by default — it debugs the alarms you already have (or identifies missing ones). The free ConvOps Audit scans your CloudWatch setup and tells you which Amazon RDS resources are missing a FreeStorageSpace alarm. ConvOps Watch then monitors FreeStorageSpace using z-score anomaly detection against a 30-day baseline, running 9 verification checks before alerting you.
Can I use ConvOps without already having a FreeStorageSpace alarm set up?+
Yes. ConvOps Watch monitors FreeStorageSpace independently of your CloudWatch alarm configuration — it reads the metric directly from CloudWatch every 5 minutes on the Growth plan. If you run the free Audit first, it will tell you which resources need a FreeStorageSpace alarm and provide the copy-paste AWS CLI command to create it.