Open Source support for OSD

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1 Open Source support for OSD IBM Haifa Research Lab IBM Labs in Haifa 2006 IBM Corporation

2 Outline IBM Labs in Haifa Object Based Storage (OSD) OSD Initiator Past Going forward OSD Simulator on AlphaWorks OSDFS Providing open source code for education and research 2

3 IBM OSD software code structure Client OSD (Object Store Device) OC ( real ) Simulator T10 Standard iscsi Target in software OSD Initiator Testing suite and Benchmarks Target (Server) iscsi Target Driver T10 Front End OC Object Controller Cache Emulator SCSI Commands IP network OSD Commands OSD Simulator Local file system Bench marks OSD Commands iscsi Tester Initiator Driver 3

4 IBM s Contributions to the Open Community In April 2005 IBM released an open-source OSD Initiator for Linux Linux Kernel Works with the iscsi initiator Required two extensions: Support for Bi-directional commands Support for large CDBs Goal is for these extensions to be included as part of the Linux Kernel In October 2005 IBM released the binaries of an OSD T10 simulator Tested with the OSD initiator Released on AlphaWorks In October 2006 IBM released OSDFS Extension to Ext2 Linux file system that works with an OSD Uses IBM s OSD initiator Released other code to universities for educational/research purposes Tester suite, OSD benchmarks U. Minnesota, enables testing an OSD implementation. Simulator code CMU. 4

5 Integration of the OSD Initiator with the SCSI Linux Stack User Application User Application User Application Linux kernel Block layer OSD layer Disk driver SD Tape driver ST CD driver SR OSD driver SO SCSI upper layer Execute SCSI command SCSI mid layer Parallel SCSI FC driver iscsi driver SCSI lower layer HBA HBA TCP 5

6 Design of the SCSI OSD initiator Requirements Allow the user to submit OSD commands, kernel mode and user mode Execute OSD commands via T10 OSD SCSI protocol Extended CDBs Bidirectional commands High level API and implementation shouldn't change for new SCSI transports API must support both iscsi and FCP transparently Allow dynamic attach/detach of devices Design Decisions Use available Open Source packages as much as possible Use Linux SCSI subsystem Proper SCSI layering focus on developing only the Object Store Device driver SCSI transport transparency 6

7 OSDFS A Linux file System over OSD File system that uses an OSD and exports the API of a standard Linux file system. Extension to the ext2 Linux file system that works with a T10 standard OSD. Uses IBM's OSD open source initiator for Linux Allows an application to use the OSD without the need to change its APIs Written and maintained by Avishay Traeger IBM Summer Intern currently a PhD student at SUNY Stony Brook. Application User space Kernel space VFS osdfs OSD Initiator SCSI iscsi 7

8 OSDFS Design On-Disk Structure The file system resides in an OSD partition Each file is currently stored in one object A directory treated as a special type of file (UNIX conventions) Simple mapping between Inode numbers and object IDs Inode Holds information needed by the file system to handle a file Persistent data saved in a user-defined attribute of the object Read into memory when file is accessed Synced to OSD if modified Superblock Holds information pertaining to the entire file system Persistent data is saved in an object with a known object ID Read into memory at mount-time Synced to disk if modified Permissions Enforces the standard UNIX permissions All requests to the OSD use good credentials A credential is created for the superblock at mount-time A credential is created for each inode when it is read into memory 8

9 Creating OSDFS with mkosdfs User-space program that creates the file system Optionally formats the LUN Creates a partition for the file system Creates the superblock Creates the root directory 9

10 Links OSD Initiator OSD Simulator OSDFS Visit our site 10

11 Backup Foils 11

12 Interfaces for SCSI mid-layer SCSI Execute-Command abstraction (SAM-3) Service Response = Execute Command ( IN ( I_T_L_Q Nexus, CDB, Task Attribute, [Data-In Buffer Size], [Data-Out Buffer], [Data-Out Buffer Size], [Command Reference Number], [Task Priority])), OUT ( [Data-In Buffer], [Sense Data], [Sense Data Length], Status )) Linux implementation of the abstraction (Linux SCSI mid-layer) void scsi_do_req(struct scsi_request *, const void *cmnd, void *buffer, unsigned bufflen, void (*done) (struct scsi_cmnd *), int timeout, int retries) Mid-layer allows only one buffer pointer and restricts CDB size to 16 12

13 Add missing functionality to the SCSI layer Bi-directional data transfer support SCSI mid layer expects a single pointer for data buffer Linux supports single buffer or scatter-gather, based on use_sg field use scatter gather 0 single buffer N number of buffers in scatter-gather list Extend mechanism to support a new bi-directional-data descriptor: struct bi-directional-data { int use_sg_out; void * data_out; int data_out_len; int use_sg_in; void * data_in; int data_in_len; } Mid layer passes down the data pointer no need to add changes to mid-layer When the bi-directional data transfer flag is on (in scsi_request), low layer driver (iscsi driver) should interpret the data pointer as pointer to a bi-directional data structure 13

14 Bi-directional data transfer (cont ) in iscsi driver Added support for AHS (Additional Header Segment) in the iscsi driver to support bi-directional data transfer. 14

15 Add missing functionality to the SCSI layer (cont ) Extended CDBs Mid-layer does not check length of CDB no problem to redefine MAX_CDB_LENGTH iscsi driver had to be extended to handle extended CDBs by adding support for AHS. 15

16 Overall structure of iscsi PDU 16

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