mirror of
https://github.com/ceph/ceph
synced 2024-12-21 10:54:42 +00:00
107 lines
3.4 KiB
ReStructuredText
107 lines
3.4 KiB
ReStructuredText
===
|
|
OSD
|
|
===
|
|
|
|
Concepts
|
|
--------
|
|
|
|
*Messenger*
|
|
See src/msg/Messenger.h
|
|
|
|
Handles sending and receipt of messages on behalf of the OSD. The OSD uses
|
|
two messengers:
|
|
|
|
1. cluster_messenger - handles traffic to other OSDs, monitors
|
|
2. client_messenger - handles client traffic
|
|
|
|
This division allows the OSD to be configured with different interfaces for
|
|
client and cluster traffic.
|
|
|
|
*Dispatcher*
|
|
See src/msg/Dispatcher.h
|
|
|
|
OSD implements the Dispatcher interface. Of particular note is ms_dispatch,
|
|
which serves as the entry point for messages received via either the client
|
|
or cluster messenger. Because there are two messengers, ms_dispatch may be
|
|
called from at least two threads. The osd_lock is always held during
|
|
ms_dispatch.
|
|
|
|
*WorkQueue*
|
|
See src/common/WorkQueue.h
|
|
|
|
The WorkQueue class abstracts the process of queueing independent tasks
|
|
for asynchronous execution. Each OSD process contains workqueues for
|
|
distinct tasks:
|
|
|
|
1. OpWQ: handles ops (from clients) and subops (from other OSDs).
|
|
Runs in the op_tp threadpool.
|
|
2. PeeringWQ: handles peering tasks and pg map advancement
|
|
Runs in the op_tp threadpool.
|
|
See Peering
|
|
3. CommandWQ: handles commands (pg query, etc)
|
|
Runs in the command_tp threadpool.
|
|
4. RecoveryWQ: handles recovery tasks.
|
|
Runs in the recovery_tp threadpool.
|
|
5. SnapTrimWQ: handles snap trimming
|
|
Runs in the disk_tp threadpool.
|
|
See SnapTrimmer
|
|
6. ScrubWQ: handles primary scrub path
|
|
Runs in the disk_tp threadpool.
|
|
See Scrub
|
|
7. ScrubFinalizeWQ: handles primary scrub finalize
|
|
Runs in the disk_tp threadpool.
|
|
See Scrub
|
|
8. RepScrubWQ: handles replica scrub path
|
|
Runs in the disk_tp threadpool
|
|
See Scrub
|
|
9. RemoveWQ: Asynchronously removes old pg directories
|
|
Runs in the disk_tp threadpool
|
|
See PGRemoval
|
|
|
|
*ThreadPool*
|
|
See src/common/WorkQueue.h
|
|
See also above.
|
|
|
|
There are 4 OSD threadpools:
|
|
|
|
1. op_tp: handles ops and subops
|
|
2. recovery_tp: handles recovery tasks
|
|
3. disk_tp: handles disk intensive tasks
|
|
4. command_tp: handles commands
|
|
|
|
*OSDMap*
|
|
See src/osd/OSDMap.h
|
|
|
|
The crush algorithm takes two inputs: a picture of the cluster
|
|
with status information about which nodes are up/down and in/out,
|
|
and the pgid to place. The former is encapsulated by the OSDMap.
|
|
Maps are numbered by *epoch* (epoch_t). These maps are passed around
|
|
within the OSD as std::tr1::shared_ptr<const OSDMap>.
|
|
|
|
See MapHandling
|
|
|
|
*PG*
|
|
See src/osd/PG.* src/osd/ReplicatedPG.*
|
|
|
|
Objects in rados are hashed into *PGs* and *PGs* are placed via crush onto
|
|
OSDs. The PG structure is responsible for handling requests pertaining to
|
|
a particular *PG* as well as for maintaining relevant metadata and controlling
|
|
recovery.
|
|
|
|
*OSDService*
|
|
See src/osd/OSD.cc OSDService
|
|
|
|
The OSDService acts as a broker between PG threads and OSD state which allows
|
|
PGs to perform actions using OSD services such as workqueues and messengers.
|
|
This is still a work in progress. Future cleanups will focus on moving such
|
|
state entirely from the OSD into the OSDService.
|
|
|
|
Overview
|
|
--------
|
|
See src/ceph_osd.cc
|
|
|
|
The OSD process represents one leaf device in the crush hierarchy. There
|
|
might be one OSD process per physical machine, or more than one if, for
|
|
example, the user configures one OSD instance per disk.
|
|
|