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RunBook Academy

← All break/fix scenarios in Ceph

advancedceph-full~30 min

Full - writes blocked cluster-wide

Reported symptoms

  • ●ceph -s reports POOL_FULL
  • ●New writes to a full pool return ENOSPC
  • ●The affected pool cannot accept new data

Evidence

  • · ceph df shows the pool at 0.95 (full_ratio)
  • · ceph health detail lists the full message
  • · ceph osd df tree shows the OSDs serving the pool at the full ratio
Diagnosis and resolutionclick to reveal

Root cause

The pool has reached mon_osd_full_ratio (default 0.95). All writes to the pool block.

Remediation

Immediate: stop non-essential writes; identify which pool; raise the threshold (last resort, temporary); add capacity; delete data.

Verification

ceph -s reports HEALTH_OK; new writes succeed; the cluster is no longer at risk.

Prevention

Plan capacity (Part LXVI); alert at 70% / 85%; rehearse the capacity response.

Architecture

The student examines the broken architecture diagram and identifies the responsible component. The cluster is running Ceph Tentacle (20.2.x); the incident is one a production operator must diagnose from the evidence presented.

Symptoms

  • ceph -s reports POOL_FULL
  • New writes to a full pool return ENOSPC
  • The affected pool cannot accept new data

Evidence

  • ceph df shows the pool at 0.95 (full_ratio)
  • ceph health detail lists the full message
  • ceph osd df tree shows the OSDs serving the pool at the full ratio

Student investigation

The student follows the methodology: define the symptom, determine the impact, gather evidence, identify the component, form a hypothesis, test safely, restore, validate.

Progressive hints

  • Hint 1: check the cluster state with ceph -s first.
  • Hint 2: read ceph health detail and identify the affected PGs / OSDs / daemons.
  • Hint 3: use ceph osd tree, ceph pg dump, or ceph mds stat as the next-level diagnostic.
  • Hint 4: the root cause is documented in the frontmatter root_cause field.

Validation

The student runs the verification steps and confirms the symptom cleared.

Root cause

See the frontmatter root_cause field.

Remediation

Apply the fix from the frontmatter remediation field.

Prevention

Apply the prevention measures from the frontmatter prevention field.