Subsystem Map

The Lustre subsystems are listed below. For each subsystem, a summary description and code is provided.

libcfs

 * Summary
 * Libcfs provides an API comprising fundamental primitives and subsystems - e.g. process management and debugging support which is used throughout LNET, Lustre, and associated utilities. This API defines a portable runtime environment that is implemented consistently on all supported build targets.


 * Code
 * lustre/lnet/libcfs/**/*.[ch]

lnet

 * Summary
 * See the Lustre Networking white paper for details.


 * Code
 * lustre/lnet/**/*.[ch]

ptlrpc
Ptlrpc implements Lustre communications over LNET. All communication between Lustre processes are handled by RPCs, in which a request is sent to an advertised service, and the service processes the request and returns a reply. Note that a service may be offered by any Lustre process - e.g. the OST service on an OSS processes I/O requests and the AST service on a client processes notifications of lock conflicts. The initial request message of an RPC is special - it is received into the first available request buffer at the destination. All other communications involved in an RPC are like RDMAs - the peer targets them specifically. For example, in a bulk read, the OSC posts reply and bulk buffers and sends descriptors for them (the LNET matchbits used to post them) in the RPC request. After the server has received the request, it GETs or PUTs the bulk data and PUTs the RPC reply directly. Ptlrpc ensures all resources involved in an RPC are freed in finite time. If the RPC does not complete within a timeout, all buffers associated with the RPC must be unlinked. These buffers are still accessible to the network until their completion events have been delivered.
 * Summary


 * Code
 * lustre/ptlrpc/*.[ch]
 * lustre/ldlm/ldlm_lib.c

llog'''
Overview LLog is the generic logging mechanism in Lustre. It allows Lustre to store records in an appropriate format and access them later using a reasonable API.
 * Summary

LLog is used is various cases. The main LLog use cases are the following:


 * mountconf - entire cluster configuration is stored on the MGS in a special configuration llog. A client may access it via an llog API working over ptlrpc;


 * MDS_OST llog - contains records for unlink and setattr operations, performed on the MDS in the last, not committed transaction. This is needed to preserve consistency between MDS and OST nodes for failure cases. General case: If the MDS does not have an inode for some file, then the OST also should not have object for the same file. So, when the OST fails in the middle of unlink and loses the last transaction containing unlink for the OST object, this may cause the object to be lost on the OST. On the MDS, the current transaction with the unlinked object has finished and the MDS has no inode for the file. This means that the file cannot be accessed later and it just eats up space on the OST. The solution is to maintain the unlink log on the MDS and process it at MDS-OST connect time to make sure the OST has all objects unlinked;


 * Size llog - this is not yet used, but is planned to log object size changes on the OST so the MDS can later check if it has object size coherence with the MDS (SOM case);


 * LOVEA llog - joins the file LOV EA merge log.

General design Each llog type has two main parts:


 * ORIG llog - "server" part, the site where llog records are stored. It provides an API for local and/or network llog access (read, modify). Examples of ORIG logs: MDS is orig for MDS_OST llog and MGS is orig for config logs;


 * REPL llog - "client" part, the site where llog records may be used. Examples of REPL logs: OST is repl for MDS_OST llog and MGC is repl for config logs.


 * Code
 * obdclass/llog.c
 * obdclass/llog_cat.c
 * obdclass/llog_lvfs.c
 * obdclass/llog_obd.c
 * obdclass/llog_swab.c
 * obdclass/llog_test.c
 * lov/lov_log.c
 * ptlrpc/llog_client.c
 * ptlrpc/llog_server.c
 * ptlrpc/llog_net.c

obdclass
The obdclass code is generic Lustre configuration and device handling. Different functional parts of the Lustre code are split into obd devices which can be configured and connected in various ways to form a server or client filesystem.
 * Summary

Several examples of obd devices include:


 * OSC - object storage client (connects over network to OST)
 * OST - object storage target
 * LOV - logical object volume (aggregates multipe OSCs into a single virtual device)
 * MDC - meta data client (connects over network to MDT)
 * MDT - meta data target

The obdclass code provides services used by all Lustre devices for configuration, memory allocation, generic hashing, kernel interface routines, random number generation, etc.


 * Code
 * lustre/obdclass/class_hash.c
 * scalable hash code for imports
 * lustre/obdclass/class_obd.c
 * base device handling code
 * lustre/obdclass/debug.c
 * helper routines for dumping data structs
 * lustre/obdclass/genops.c
 * device allocation/configuration/connection
 * lustre/obdclass/linux-module.c
 * linux kernel module handling
 * lustre/obdclass/linux-obdo.c
 * pack/unpack obdo and other IO structs
 * lustre/obdclass/linux-sysctl.c
 * /proc/sys configuration parameters
 * lustre/obdclass/lprocfs_status.c
 * /proc/fs/lustre configuration/stats, helpers
 * lustre/obdclass/lustre_handles.c
 * wire opaque pointer handlers
 * lustre/obdclass/lustre_peer.c
 * peer target identification by UUID
 * lustre/obdclass/obd_config.c
 * configuration file parsing
 * lustre/obdclass/obd_mount.c
 * server filesystem mounting
 * lustre/obdclass/obdo.c
 * more obdo handling helpers
 * lustre/obdclass/statfs_pack.c
 * statfs helpers for wire pack/unpack
 * lustre/obdclass/uuid.c
 * UUID pack/unpack
 * lustre/lvfs/lvfs_common.c
 * kernel interface helpers
 * lustre/lvfs/lvfs_darwin.c
 * darwin kernel helper routines
 * lustre/lvfs/lvfs_internal.h
 * lvfs internal function prototypes
 * lustre/lvfs/lvfs_lib.c
 * statistics
 * lustre/lvfs/lvfs_linux.c
 * linux kernel helper routines
 * lustre/lvfs/lvfs_userfs.c
 * userspace helper routines
 * lustre/lvfs/prng.c
 * long period pseudo-random number generator
 * lustre/lvfs/upcall_cache.c
 * supplementary group upcall for MDS

luclass
luclass is a body of data-type definitions and functions implementing support for a layered object, that is an entity where every layer in the Lustre device stack (both data and meta-data, and both client and server side) can maintain its own private state, and modify a behavior of a compound object in a systematic way.
 * Summary

Specifically, data-types are introduced, representing a device type (struct lu_device_type, layer in the Lustre stack), a device (struct lu_device, a specific instance of the type), and object (struct lu_object). Following lu_object functionality is implemented by a generic code:


 * Compound object is uniquely identified by a FID, and is stored in a hash table, indexed by a FID;


 * Objects are kept in a LRU list, and a method to purge least recently accessed objects in reaction to the memory pressure is provided;


 * Objects are reference counted, and cached;


 * Every object has a list of layers (also known as slices), where devices can store their private state. Also, every slice comes with a pointer to an operations vector, allowing device to modify object's behavior.

In addition to objects and devices, luclass includes lu_context, which is a way to efficiently allocate space, without consuming stack space.

luclass design is specified in the MD API DLD.


 * Code
 * include/lu_object.h
 * obdclass/lu_object.c

ldlm
The Lustre Distributed Lock Manager (LDLM) is the Lustre locking infrastructure; it handles locks between clients and servers and locks local to a node. Different kinds of locks are available with different properties. Also as a historic heritage, ldlm happens to have some of the generic connection service code (both server and client).
 * Summary


 * Code
 * interval_tree.c
 * This is used by extent locks to maintain interval trees (bug 11300).
 * l_lock.c
 * Resourse locking primitives.
 * ldlm_extent.c
 * Extents locking code used for locking regions inside objects.
 * ldlm_flock.c
 * Bsd and posix locking lock types.
 * ldlm_inodebits.c
 * Inodebis locks used for metadata locking.
 * ldlm_lib.c
 * Target and client connecting/reconnecting/recovery code. Does not really belong to ldlm, but is historically placed there. Should be in ptlrpc instead.
 * ldlm_lock.c
 * This source file mostly has functions dealing with struct.
 * ldlm_lock ldlm_lockd.c
 * Functions that imply replying to incoming lock-related rpcs (that could be both on server (lock enq/cancel/...) and client (ast handling)).
 * ldlm_plain.c
 * Plain locks, predecessor to inodebits locks; not widely used now.
 * ldlm_pool.c
 * Pools of locks, related to dynamic lrus and freeing locks on demand.
 * ldlm_request.c
 * Collection of functions to work with locks based handles as opposed to lock structures themselves.
 * ldlm_resource.c
 * Functions operating on namespaces and lock resources.
 * include/lustre_dlm.h
 * Important defines and declarations for ldlm.

fids
FID is unique object identifier in cluster since 1.7. It has few properties, main of them are the following:
 * Summary


 * FID is unique and not reused object identifier;
 * FID is allocated by client inside of the sequence granted by server;
 * FID is base for ldlm resource used for issuing ldlm locks. This is because FID is unique and as such good for this using;
 * FID is base for building client side inode numbers as we can't use server inode+generation anymore, in CMD this is not unique combination;
 * FID does not contain store information like inode number or generation and as such easy to migrate;

FID consists of 3 fields:


 * f_seq - sequence number
 * f_oid - object identifier inside sequence
 * f_ver - object version


 * Code
 * fid/fid_request.c
 * fid/fid_lib.c
 * fld/*.[ch]

seq

 * Summary


 * Overview

Sequence management is a basic mechanism in new MDS server which is related to managing FIDs. FID is an unique object identifier in Lustre starting from version 1.7. All FIDs are organized into sequences. One sequence is number of FIDs. Sequences are granted/allocated to clients by servers. FIDs are allocated by clients inside granted sequence. All FIDs inside one sequence live on same MDS server and as such are one "migration unit" and one "indexing unit", meaning that FLD (FIDs Location Database) indexes them all using one sequence and thus has only one mapping entry for all FIDs in sequence. Please read section devoted to FIDs bellow in the root table to find more info on FLD service and FIDs. A sequence has the limit of FIDs to be allocated in it. When this limit is reached, new sequence is allocated. Upon disconnect, server allocates new sequence to the client when it comes back. Previously used sequence is abandoned even if it was not exhausted. Sequences are valuable resource but in the case of recovery, using new sequence makes things easier and also allows to group FIDs and objects by working sessions, new connection - new sequence.

Code description

Server side code is divided into two parts:


 * Sequence controller - allocates super-sequences, that is, sequences of sequences to all servers in cluster (currently only to MDSes as only they are new FIDs aware). Usually first MDS in cluster is sequence controller


 * Sequence manager - allocates meta-sequences (smaller range of sequences inside a super-sequence) to all clients, using granted super-sequence from the sequence controller. All MDSs in the cluster (all servers in the future) are sequence managers. The first MDS is, simultaneously, a sequence controller and a sequence manager.

Client side code allocates new sequences from granted meta-sequence. When meta-sequence is exhausted, new one is allocated on server and sent to the client. Client code consists of API for working with both server side parts, not only with sequence manager as all servers need to talk to sequence controller, they also use client API for this. One important part of client API is FIDs allocation. New FID is allocated in currently granted sequence until sequence is exhausted.


 * Code
 * fid/fid_handler.c - server side sequence management code;
 * fid/fid_request.c - client side sequence management code;
 * fid/fid_lib.c - fids related miscellaneous stuff.

mountconf
MountConf is how servers and clients are set up, started, and configured. A MountConf usage document is here. The major subsystems are the MGS, MGC, and the userspace tools mount.lustre and mkfs.lustre. The basic idea is:
 * Summary


 * 1) Whenever any Lustre component is mount(2)ed, we start a MGC.
 * 2) This establishes a connection to the MGS and downloads a configuration llog.
 * 3) The MGC passes the configuration log through the parser to set up the other OBDs.
 * 4) The MGC holds a CR configuration lock, which the MGS recalls whenever a live configuration change is made.


 * Code


 * MountConf file areas:


 * lustre/mgs/*
 * lustre/mgc/*
 * lustre/obdclass/obd_mount.c
 * lustre/utils/mount_lustre.c
 * lustre/utils/mkfs_lustre.c

liblustre
Liblustre is a userspace library, used along with libsysio (developed by Sandia), that allows Lustre usage just by linking (or ld_preload'ing) applications with it. Liblustre does not require any kernel support. It is also used on old Cray XT3 machines (and not so old, in the case of Sandia), where all applications are just linked with the library and loaded into memory as the only code to run. Liblustre does not support async operations of any kind due to a lack of interrupts and other notifiers from lower levels to Lustre. Liblustre includes another set of LNDs that are able to work from userspace.
 * Summary


 * Code
 * dir.c
 * Directory operations
 * file.c
 * File handling operations (like open)
 * llite_lib.c
 * General support (init/cleanp/parse options)
 * lutil.c
 * Supplementary code to get IP addresses and init various structures needed to emulate the normal Linux process from other layers' perspective.
 * namei.c
 * Metadata operations code.
 * rw.c
 * I/O code, including read/write
 * super.c
 * "Superblock" operation - mounting/umounting, inode operations.tests - directory with liblustre-specific tests.

echo client/server
The echo_client and obdecho are OBD devices which help testing and performance measurement. They were implemented originally for network testing - obdecho can replace obdfilter and echo_client can exercise any downstream configurations. They are normally used in the following configurations:
 * Summary


 * echo_client -> obdfilter. This is used to measure raw backend performance without any network I/O.
 * echo_client -> OSC -> -> OST -> obdecho. This is used to measure network and ptlrpc performance.
 * echo_client -> OSC -> -> OST -> obdfilter. This is used to measure performance available to the Lustre client.


 * Code
 * lustre/obdecho/

client vfs
The client VFS interface, also called llite, is the bridge between the Linux kernel and the underlying Lustre infrastructure represented by the LOV, MDC, and LDLM subsystems. This includes mounting the client filesystem, handling name lookups, starting file I/O, and handling file permissions. The Linux VFS interface shares a lot in common with the liblustre interface, which is used in the Catamount environment; as of yet, the code for these two subsystems is not common and contains a lot of duplication.
 * Summary


 * Code
 * lustre/llite/dcache.c
 * Interface with Linux dentry cache/intents
 * lustre/llite/dir.c
 * readdir handling, filetype in dir, dir ioctl
 * lustre/llite/file.c
 * File handles, file ioctl, DLM extent locks
 * lustre/llite/llite_close.c
 * File close for opencache
 * lustre/llite/llite_internal.h
 * Llite internal function prototypes, structures
 * lustre/llite/llite_lib.c
 * Majority of request handling, client mount
 * lustre/llite/llite_mmap.c
 * Memory-mapped I/O
 * lustre/llite/llite_nfs.c
 * NFS export from clients
 * lustre/llite/lloop.c
 * Loop-like block device export from object
 * lustre/llite/lproc_llite.c
 * /proc interface for tunables, statistics
 * lustre/llite/namei.c
 * Filename lookup, intent handling
 * lustre/llite/rw24.c
 * Linux 2.4 IO handling routines
 * lustre/llite/rw26.c
 * Linux 2.6 IO handling routines
 * lustre/llite/rw.c
 * Linux generic IO handling routines
 * lustre/llite/statahead.c
 * Directory statahead for "ls -l" and "rm -r"
 * lustre/llite/super25.c
 * Linux 2.6 VFS file method registration
 * lustre/llite/super.c
 * Linux 2.4 VFS file method registration
 * lustre/llite/symlink.c
 * Symbolic links
 * lustre/llite/xattr.c
 * User-extended attributes

client vm
Client code interacts with VM/MM subsystems of the host OS kernel to cache data (in the form of pages), and to react to various memory-related events, like memory pressure. Two key components of this interaction are:
 * Summary


 * cfs_page_t data-type representing MM page. It comes together with the interface to map/unmap page to/from kernel virtual address space, access various per-page bits, like 'dirty', 'uptodate', etc., lock/unlock page. Currently, this data-type closely matches the Linux kernel page. It has to be straightened out, formalized, and expanded to include functionality like querying about total number of pages on a node, etc.


 * MM page operations in cl_page (part of new client I/O interface).


 * Code

This describes the next generation Lustre client I/O code, which is expected to appear in Lustre 2.0. Code location is not finalized. cfs_page_t interface is defined and implemented in:


 * lnet/include/libcfs/ARCH/ARCH-mem.h
 * lnet/libcfs/ARCH/ARCH-mem.c

Generic part of cl-page will be located in:


 * include/cl_object.h
 * obdclass/cl_page.c
 * obdclass/cl_object.c

Linux kernel implementation is currently in:


 * llite/llite_cl.c

client I/O
Client I/O is a group of interfaces used by various layers of a Lustre client to manage file data (as opposed to metadata). Main functions of these interfaces are:
 * Summary


 * Cache data, respecting limitations imposed both by hosting MM/VM, and by cluster-wide caching policies, and
 * Form a stream of efficient I/O RPCs, respecting both ordering/timing constraints imposed by the hosting VFS (e.g., POSIX guarantees, O_SYNC, etc.), and cluster-wide IO scheduling policies.

Client I/O subsystem interacts with VFS, VM/MM, DLM, and PTLRPC. Client I/O interfaces are based on the following data-types:


 * cl_object: represents a file system object, both a file, and a stripe;
 * cl_page: represents a cached data page;
 * cl_lock: represents an extent DLM lock;
 * cl_io: represents an ongoing high-level IO activity, like read(2)/write(2) system call, or sub-io of another IO;
 * cl_req: represents a network RPC.

This describes the next generation Lustre client I/O code. The code location is not finalized. The generic part is at:
 * Code


 * include/cl_object.h
 * obdclass/cl_object.c
 * obdclass/cl_page.c
 * obdclass/cl_lock.c
 * obdclass/cl_io.c

Layer-specific methods are currently at


 * lustre/LAYER/LAYER_cl.c

where LAYER is one of llite, lov, osc.

client metadata
The Meta Data Client (MDC) is the client-side interface for all operations related to the Meta Data Server MDS. In current configurations there is a single MDC on the client for each filesystem mounted on the client. The MDC is responsible for enqueueing metadata locks (via LDLM), and packing and unpacking messages on the wire. In order to ensure a recoverable system, the MDC is limited at the client to only a single filesystem-modifying operation in flight at one time. This includes operations like create, rename, link, unlink, setattr. For non-modifying operations like getattr and statfs the client can multiple RPC requests in flight at one time, limited by a tunable on the client, to avoid overwhelming the MDS.
 * Summary


 * Code
 * lustre/mdc/lproc_mdc.c
 * /proc interface for stats/tuning
 * lustre/mdc/mdc_internal.h
 * Internal header for prototypes/structs
 * lustre/mdc/mdc_lib.c
 * Packing of requests to MDS
 * lustre/mdc/mdc_locks.c
 * Interface to LDLM and client VFS intents
 * lustre/mdc/mdc_reint.c
 * Modifying requests to MDS
 * lustre/mdc/mdc_request.c
 * Non-modifying requests to MDS

client lmv
LMV is a module which implements CMD client-side abstraction device. It allows client to work with many MDSes without any changes in Llite module and even without knowing that CMD is supported. Llite just translates Linux VFS requests into metadata API calls and forwards them down to the stack. As LMV needs to know which MDS to talk for any particular operation, it uses some new services introduced in CMD3 times. They are:
 * Summary


 * FLD (Fids Location Database) - having FID or rather its sequence, lookup MDS number where this FID is located;
 * SEQ (Client Sequence Manager) - LMV uses this via children MDCs for allocating new sequences and FIDs.

LMV supports split objects. This means that for every split directory it creates special in-memory structure which contains information about object stripes. This includes MDS number, FID, etc. All consequent operations use these structures for determining what MDS should be used for particular action (create, take lock, etc).


 * Code
 * lmv/*.[ch]

lov
The LOV device presents a single virtual device interface to upper layers (llite, liblustre, MDS). The LOV code is responsible for splitting of requests to the correct OSTs based on striping information (lsm), and the merging of the replies to a single result to pass back to the higher layer. It calculates per-object membership and offsets for read/write/truncate based on the virtual file offset passed from the upper layer. It is also responsible for splitting the locking across all servers as needed. The LOV on the MDS is also involved in object allocation.
 * Summary


 * Code
 * lustre/lov/lov_ea.c
 * Striping attributes pack/unpack/verify
 * lustre/lov/lov_internal.h
 * Header for internal function prototypes/structs
 * lustre/lov/lov_merge.c
 * Struct aggregation from many objects
 * lustre/lov/lov_obd.c
 * Base LOV device configuration
 * lustre/lov/lov_offset.c
 * File offset and object calculations
 * lustre/lov/lov_pack.c
 * Pack/unpack of striping attributes
 * lustre/lov/lov_qos.c
 * Object allocation for different OST loading
 * lustre/lov/lov_request.c
 * Request handling/splitting/merging
 * lustre/lov/lproc_lov.c
 * /proc/fs/lustre/lov tunables/statistics

{| border="1" cellspacing=0 cellpadding="5" CMM
 * colspan="2" valign="top |
 * Summary
 * ===Overview===
 * ===Overview===

The CMM is a new layer in the MDS which cares about all clustered metadata issues and relationships. The CMM does the following:


 * Acts as layer between the MDT and MDD.
 * Provides MDS-MDS interaction.
 * Queries and updates FLD.
 * Does the local or remote operation if needed.
 * Will do rollback - epoch control, undo logging.

CMM functionality
CMM chooses all servers involved in operation and sends depended request if needed. The calling of remote MDS is a new feature related to the CMD. CMM mantain the list of MDC to connect with all other MDS.

Objects
The CMM can allocate two types of object - local and remote. Remote object can occur during metadata operations with more than one object involved. Such operation is called as cross-ref operation. lustre/cmm
 * Code
 * Code
 * }

{| border="1" cellspacing=0 cellpadding="5" recovery
 * colspan="2" valign="top |
 * Summary
 * Summary

Overview
Client recovery starts in case when no server reply is received within given timeout or when server tells to client that it is not connected (client was evicted on server earlier for whatever reason).

The recovery consists of trying to connect to server and then step through several recovery states during which various client-server data is synchronized, namely all requests that were already sent to server but not yet confirmed as received and DLM locks. Should any problems arise during recovery process (be it a timeout or server’s refuse to recognise client again), the recovery is restarted from the very beginning.

During recovery all new requests to the server are not sent to the server, but added to special delayed requests queue that is then sent once if recovery completes succesfully.

Replay and Resend
Recovery code is scattered through all code almost. Though important code: ldlm/ldlm_lib.c - generic server recovery code ptlrpc/ - client recovery code
 * Clients will go through all the requests in the sending and replay lists and determine the recovery action needed - replay request, resend request, cleanup up associated state for committed requests.
 * The client replays requests which were not committed on the server, but for which the client saw reply from server before it failed. This allows the server to replay the changes to the persistent store.
 * The client resends requests that were committed on the server, but the client did not see a reply for them, maybe due to server failure or network failure that caused the reply to be lost. This allows the server to reconstruct the reply and send it to the client.
 * The client resends requests that the server has not seen at all, these would be all requests with transid higher than the last_rcvd value from the server and the last_committed transno, and the reply seen flag is not set.
 * The client gets the last_committed transno information from the server and cleans up the state associated with requests that were committed on the server.
 * Code
 * Code
 * }

{| border="1" cellspacing=0 cellpadding="5" version recovery
 * colspan="2" valign="top |
 * Summary
 * Summary

Version Based Recovery
This recovery technique is based on using versions of objects (inodes) to allow clients to recover later than ordinary server recovery timeframe.

Recovery code is scattered through all code almost. Though important code: ldlm/ldlm_lib.c - generic server recovery code ptlrpc/ - client recovery code
 * 1) The server changes the version of object during any change and return that data to client. The version may be checked during replay to be sure that object is the same state during replay as it was originally.
 * 2) After failure the server starts recovery as usual but if some client miss the version check will be used for replays.
 * 3) Missed client can connect later and try to recover. This is 'delayed recovery' and version check is used during it always.
 * 4) The client which missed main recovery window will not be evicted and can connect later to initiate recovery. In that case the versions will checked to determine was that object changed by someone else or not.
 * 5) When finished with replay, client and server check if any replay failed on any request because of version mismatch. If not, the client will get a successful reintegration message. If a version mismatch was encountered, the client must be evicted.
 * Code
 * Code
 * }

{| border="1" cellspacing=0 cellpadding="5" pCIFS, CTDB
 * colspan="2" valign="top |
 * Summary
 * ===pCIFS Overview===
 * Lustre pCIFS client provides parallel I/O support to Lustre servers shared by Samba via CIFS protocol. All data I/O is to be dispatched smartly to Lustre OST nodes while the metadata operations will be kept untouched and go directly to Lustre MDS server.
 * Lustre pCIFS client provides parallel I/O support to Lustre servers shared by Samba via CIFS protocol. All data I/O is to be dispatched smartly to Lustre OST nodes while the metadata operations will be kept untouched and go directly to Lustre MDS server.

The pCIFS client is actually a Samba client via CIFS protocol, not a native Lustre client via Lustre LNET protocol. It is implemented as a Windows file filter driver upon Windows network file system (LanmanRedirector) to detect user i/o requests and redirect the requests to the corresponding OST nodes rather than the MDS node to eliminate the bottleneck in MDS node. Here's the architecture picture:

Currently a beta version is out for public test. The coming version will have failover supported.

pCIFS Architecture:


 * CTDB/Samba

CTDB is a database implementation, providing TDB-like APIs to Samba or other applications for temporary context data management. It relies the underlying clustered filesystem to manage TDB database files, since TDB uses FLOCK to protect database access.

As TDB database is shared to all nodes in the cluster, CTDB provides failover to all CTDB clients (like Samba). When a Samba/CTDB node hangs, another node will takeover the dead node's IP address and restore all TCP connections. The failover process is completely transparent, so the Samba client won't notice the failover process and will stay alive with the new cluster configuration.

More information is available at.

CTDB Architecture:

Correction: "CTDB Private Network" and "CTDB Public Network" should be exchanged since they are marked at wrong places in the following 3 pictures.

CTDB Failover:

pCIFS Failover
lustre/lnet/libcfs/**/*.[ch]
 * Code
 * Code
 * }