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This document is for a development version of Ceph.

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OSD developer documentation

Contents

• Asynchronous Recovery
• Backfill Reservation
• Erasure Coded Placement Groups
  • Glossary
  • Table of contents
    • Developer notes
      • Introduction
      • Reading and writing encoded chunks from and to OSDs
      • Erasure code library
      • Notes
    • Jerasure plugin
      • Introduction
    • ECBackend Implementation Strategy
      • Miscellaneous initial design notes
        • PGTemp and Crush
        • Distinguished acting set positions
        • Object Classes
        • Scrub
        • Crush
    • ECBackend
      • MAIN OPERATION OVERVIEW
        • WHOLE STRIPE WRITE
        • READ-MODIFY-WRITE
        • OSD Object Write and Consistency
        • ExtentCache
        • Pipeline
    • Erasure coding enhancements design document
      • Objectives
        • Current Read Implementation
        • Partial Reads
        • Current Overwrite Implementation
        • Partial Overwrites
        • Parity-delta-write
        • Direct Read I/O
        • Distributed processing of writes
        • Direct Write I/O
        • Larger chunk size
      • Design
        • Test tools
        • I/O path changes
          • Avoid unnecessary reads and writes
          • Parity-delta-write
          • Direct reads
          • Direct writes
            • I/O serialization, recovery/backfill and other error scenarios
          • Stripe cache
          • Automatically choose chunk size
          • Deep scrub support
        • Metadata changes
          • How many copies of metadata are required?
          • M+1 arbitrarily distributed copies
          • M+1 copies on known shards
          • Partial Writes and the PG log
          • Backfill
            • Code references
          • Version number and last modification time for clients
          • Direct Write with Metadata updates
        • Upgrade and backwards compatibility
        • Not under consideration
      • Stories
        • Test tools - enhanced I/O generator for testing erasure coding
        • Test tools - offline consistency checking tool
        • Test tools - online consistency checking tool
        • Switch for JErasure to ISA-L
        • Sub Stripe Reads
        • Simple Optimizations to Overwrite
        • Eliminate unnecessary chunk writes but keep metadata transactions
        • Avoid zero padding objects to a full stripe
        • Erasure coding plugin changes to support distributed partial writes
        • Erasure coding interface to allow RADOS clients to direct I/Os to OSD storing the data
        • Changes to object_info_t
        • Changes to PGLog and Peering to support updating a subset of OSDs
        • Change to selection of (acting) primary
        • Implement parity-delta-write with all computation on the primary
        • Upgrades and backwards compatibility
        • Changes to Backfill to use the vector in object_info_t
        • Test tools - offline metadata validation tool
        • Eliminate transactions on OSDs not updating data chunks
        • Direct reads to OSDs (single chunk only)
        • Direct reads to OSDs (multiple chunks)
        • Implement distributed parity-delta-write
        • Test tools - EC error injection thrasher
        • Implement prefetch message MOSDEcSubOpPrefetch and modify extent cache
        • Implement sequencing message MOSDEcSubOpSequence
        • Direct writes to OSD (single chunk only)
        • Direct writes to OSD (multiple chunks)
        • Deep scrub / CRC
        • Variable chunk size erasure coding
        • CLAY Erasure Codes
• last_epoch_started
• Log Based PG
  • Background
    • Why PrimaryLogPG?
    • Primary log-based replication
  • ReplicatedBackend/ECBackend unification strategy
    • PGBackend
  • PGBackend Interface Explanation
    • Readable vs Degraded
    • Client Reads
    • Scrubs
    • Recovery
• Manifest
  • Introduction
  • Intended Usage Model
    • RBD
    • RadosGW
  • Status and Future Work
    • Cleanups
    • Testing
    • Snapshots
  • Data Structures
  • Request Handling
  • RADOS Interface
  • ceph-dedup-tool
• Map and PG Message handling
  • Overview
  • MOSDMap
  • MOSDPGOp/MOSDPGSubOp
  • CEPH_MSG_OSD_OP processing
  • Peering Messages
• QoS Study with mClock and WPQ Schedulers
  • Introduction
  • Overview
  • Test Environment
  • Test Methodology
  • Establish Baseline Client Throughput (IOPS)
  • MClock Profile Allocations
    • high_client_ops(default)
    • balanced
    • high_recovery_ops
    • custom
  • Recovery Test Steps
    • Test Steps(Using cbt)
    • Non-Default Ceph Recovery Options
  • Test Results
    • Test Results With NVMe SSDs
      • Client Throughput Comparison
      • Client Latency Comparison
      • Recovery Statistics Comparison
    • Test Results With HDDs (WAL and dB configured)
      • Client Throughput & latency Comparison
      • Recovery Statistics Comparison
    • Test Results With HDDs (No WAL and dB configured)
      • Client Throughput & latency Comparison
      • Recovery Statistics Comparison
  • Key Takeaways and Conclusion
• OSD
  • Concepts
  • Overview
• Partial Object Recovery
  • Procedures for Partial Object Recovery
• OSDMap Trimming and PastIntervals
  • PastIntervals
  • Maintenance and Trimming
  • OSDMap Trimming
  • Back to PastIntervals
  • OSDSuperblock::maps
• PG
  • Concepts
  • Peering Details and Gotchas
• PG Removal
• PGPool
• Recovery Reservation
  • Dump Reservations
  • Things to Note
  • See Also
• Refcount
  • Introduction
  • Class Interface
• Scrub internals and diagnostics
  • Scrubbing Behavior Table
  • State variables
  • Scrub Reservations
• Snaps
  • Overview
  • Ondisk Structures
  • Snap Removal
  • Recovery
  • SnapMapper
  • Split
  • clone_overlap
• Preventing Stale Reads
  • readable_until
  • Prior Intervals
  • PG “laggy” state
  • PG “wait” state
  • Dead OSDs
• Watch Notify
  • Overview
  • Watch Lifecycle
  • Notify Lifecycle
• Writeback Throttle

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