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← All break/fix scenarios in Ceph

advancedceph-nearfull~25 min

Pool reports nearfull - recovery is constrained

Reported symptoms

  • ●ceph -s reports POOL_NEARFULL
  • ●ceph df shows the pool utilisation above 0.85
  • ●Recovery continues but backfill starts to wait

Evidence

  • · ceph osd df tree identifies which OSD is nearfull
  • · ceph health detail lists the nearfull message
  • · ceph progress reports backfill running but slower than expected
Diagnosis and resolutionclick to reveal

Root cause

A pool is at the nearfull ratio (default 0.85). Backfill is restricted; recovery is constrained.

Remediation

Add capacity (Part LXIII); rebalance (Part XCIII); do not raise the threshold.

Verification

ceph -s reports HEALTH_OK; the pool is no longer nearfull; backfill resumes; recovery completes.

Prevention

Plan capacity (Part LXVI); alert at 75% / 85%; rehearse the capacity response quarterly.

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_NEARFULL
  • ceph df shows the pool utilisation above 0.85
  • Recovery continues but backfill starts to wait

Evidence

  • ceph osd df tree identifies which OSD is nearfull
  • ceph health detail lists the nearfull message
  • ceph progress reports backfill running but slower than expected

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.