Cost Optimization with Storage Tiers

Most Crab repositories follow a heavy-tail access pattern: a small hot set of files is read continuously while a long cold tail is rarely touched. Without lifecycle rules, every byte pays the Standard-tier rate regardless of access frequency.

Crab's tiering system generates provider-specific lifecycle rules that automatically transition cold xorbs through cheaper storage classes on a configurable schedule.

How It Works

crab tier plan generates lifecycle rules scoped to the .crab/xorbs/ prefix only. Metadata (shards, file-index, refs, manifests) is never tiered — it must stay warm for fast access.

Quick Start

1. Preview the lifecycle plan

crab tier plan

Read-only — probes the bucket and prints what Crab would apply. No write credentials needed.

2. Apply the plan

crab tier plan --apply

Crab writes a backup of the current lifecycle configuration, then submits the new rules via CAS to prevent races.

3. Roll back if needed

crab tier rollback .crab/tier/backups/2026-04-27T20:00:00Z-pre-apply.json

Restores the previous lifecycle configuration.

Configuration

All tiering settings live under [tier] in .crab/config.toml:

[tier]
enabled = true
to_ia_days = 30          # Days before warm transition
to_deep_days = 180       # Days before cold transition
noncurrent_days = 30     # Noncurrent version expiration
restore_tier = "standard"
restore_duration_days = 7

Restore-Aware Hydration

When crab hydrate encounters an archived xorb, it automatically initiates a restore and polls until the object is readable:

# Hydrate with default restore tier
crab hydrate --all

# Use expedited restore for urgent access
crab hydrate --all --restore-tier=expedited

# Fail immediately on archived objects (no restore)
crab hydrate --all --no-restore

Restore Availability by Storage Class

Merge Mode

If your bucket has existing lifecycle rules (from Terraform, CloudFormation, etc.), use --merge to preserve them:

crab tier plan --apply --merge

With --merge, Crab replaces only rules with crab- prefixed IDs and leaves all other rules untouched.

Minimum Retention Periods

Deleting an object before its minimum retention period incurs an early-deletion penalty. crab gc blocks early deletes by default and reports the estimated cost.

Rollback and Safety

Every tier plan --apply writes a backup before modifying the bucket:

.crab/tier/backups/<RFC3339-ts>-pre-apply.json

If the bucket's lifecycle has been modified since the backup was taken, the CAS guard detects the conflict and the rollback fails safely.

Common Workflow

# 1. Baseline cost snapshot
crab doctor --cost --json > before.json

# 2. Review the plan
crab tier plan

# 3. Apply
crab tier plan --apply

# 4. Wait for provider evaluation (S3 ~24h, GCS ~24h, Azure up to 7d)

# 5. Compare costs
crab doctor --cost --json > after.json

CLI Reference

For complete command syntax and all available flags, see the crab tier reference.