OSD-2 & XAM Erik Riedel Seagate Technology May 2007
A presentation at Intelligent Storage Workshop in May 2007 in Minneapolis, MN, USA by erik riedel
OSD-2 & XAM Erik Riedel Seagate Technology May 2007
OSD-1 Commands OSD-1 r10, as ratified in September 2004 Security • Authorization – each request • Integrity – for args & data very basic • SET KEY shared space mgmt • SET MASTER KEY secrets Groups attributes • CREATE COLLECTION • timestamps • vendor-specific • REMOVE COLLECTION • opaque • LIST COLLECTION Specialized • shared • FLUSH COLLECTION • FORMAT OSD Management • APPEND – write w/o offset • CREATE PARTITION • CREATE & WRITE – save msg • REMOVE PARTITION • FLUSH – force to media • FLUSH PARTITION • FLUSH OSD – device-wide • PERFORM SCSI COMMAND • LIST – recovery of objects • PERFORM TASK MGMT Basic Protocol • READ • WRITE • CREATE • REMOVE • GET ATTR • SET ATTR Intelligent Storage, May 2007
Status of OSD-2 Standard Standard OSD-1 r10 for Project T10/1355-D (v1) ratified by ANSI in September 2004 after five years of SNIA effort Draft OSD-2 r1 is out as of January 2007 • Currently being reviewed (take a look, send comments!) SNIA TWG working on v2 features • • • • • • • • Richer collections – multi-object operations [in OSD-2 r1] Snapshots – managed on-device [proposal] Extended exception handling and recovery [proposal] Additional security support [proposal] Additional features (reservations, CLEAR, PUNCH) [proposal] Mapping of XAM onto OSD [ongoing w/ FCAS TWG] Quality of Service attributes [discussion] Device-to-device communication [discussion] Expect OSD-2 r2 in August/September 2007 Intelligent Storage, May 2007
OSD-2 Richer Collections Current (OSD-1) definition is preserved • Two extensions are backward compatible Stronger LIST and LIST COLLECTION Commands • Return some member object attributes along with each OID • Similar to READDIRPLUS in NFSv3 Multi-object operations • Execute a single command on multiple objects - Simplicity and performance • Use of “cloned” collections for status of multi-object operations • QUERY – search attributes, returns list of matching objects • REMOVE MEMBER OBJECTS – bulk remove • SET MEMBER ATTRIBUTES – bulk attribute update • GET MEMBER ATTRIBUTES – bulk attribute retrieval Intelligent Storage, May 2007
OSD-2 Exception Management Media error handling – fencing, error maps, recovery • Report object-level errors, enable hosts or controllers to recover Atomicity & Isolation – reported by devices • Atomicity – complete an entire write or do not commit any data - Atomicity can be guaranteed on data, attributes or both - Reported using atomicity sizes: A, D, and C- limits - (limits may be zero) • Isolation – not interleaving overlapping reads/writes - strong (per command); weak (per phase); none File system check (OSD_FSCK) – externally-directed recovery Boot epoch – updated on device reboot • Prevents clients from performing commands on corrupted data • Device-level attribute encoded into each capability, can be set by file manager and may be incremented on device reboot Intelligent Storage, May 2007
OSD-2 Snapshots Snapshots are point-in-time copies of partitions Requires two credentials: one for source, one for destination SNAPSHOT CREATE • Creates a copy of the partition object and copies the content of the source partition to the newly created partition (snapshot) • Either full copy (byte-by-byte) or COW are possible DIFF READ • Compares two objects Snapshot chains handled via newly defined attributes • Forward/backward pointers • Destination pointers COPY/CLONE can be applied to individual objects • Used to create cloned collections for multi-object operations Intelligent Storage, May 2007
Additional Changes in OSD-2 Extended Collections Exception Management Snapshots Security • Support extended collections and snapshots, including multi-object capabilities Miscellaneous proposals • • • • • • • • FC & SAS issue resolution with transfer of unused bytes Alignment issue with Attribute Lists 64-bit CDB Alignment issue Read-past-end-of-object semantics Setting attribute without data buffer Reservations Range-based FLUSH CLEAR & PUNCH commands Intelligent Storage, May 2007
XAM over OSD
eXtensible Access Method (XAM) Goals See SNIA tutorial “Green Eggs and XAM”, April 2007 for additional details Compliance • Integrated record retention and disposition metadata Standardized ILM (Information Lifecycle Management) • Extensible metadata allows for external data classification and annotation • Standardized ILM policies and ILM practices, managed by systems Universal access to reference data • Application independent and long-term storage and retrieval • Application independent query interface Standards-based interoperability • XAM-compliant apps work with any XAM storage systems from any vendor • Rich metadata allows multiple applications to share information • Information can be easily migrated among XAM systems Driven by application vendors, analysts, ecosystem providers, and customers Intelligent Storage, May 2007
XAM History Today – FCAS TWG working on official API specification Q2 2006 – FCAS TWG counts >30 member companies, technical work in full progress Q4 2005 – XAM Team donates v1.2 of XAM Spec to SNIA; Donation accepted, placed under control of FCAS TWG mid Q3 2005 – XAM Team presents v1.1 to a select set of application ISVs, receives encouraging feedback early Q3 2005 – v1.0 of XAM Spec available, HP, HDS, Sun endorse XAM, join XAM Team Q4 2004 – IBM and EMC formulate a joint vision and begin work on a proposal Intelligent Storage, May 2007
XAM Status FCAS Technical Work Group (TWG) • V0.6 XAM Specification – just released (11 May) - open to feedback from SNIA members; available to public RSN • V0.9 – targeted for September 2007 • V1.0 – targeted for December 2007 (previously October 2007) XAM SDK Technical Work Group (TWG) • • • • • Technical group recently formed to develop XAM reference software Currently 18 members (6 companies/institutions) Free to join, requires companies to sign the new SNIA IP Policy Current work items are: XAM Library and Reference VIM (on a FS) OSD VIM is proposed as a work item and currently being voted on XAM Initiative • A set of companies promoting development of XAM software • Determines the priorities of the XAM SDK TWG • Fee-based membership to support development activities Intelligent Storage, May 2007
XAM Architecture (1) An application uses the libxam.dll to ‘connect’ to a specified XSystem. • A single application may connect to multiple XSystems simultaneously • Multiple applications may connect to a single XSystem simultaneously An XSystem is not identical to a vendor’s “storage box”, but a logical abstraction which should be viewed as ‘bag of storage’. The application may be required to authenticate at the time the connection to an XSystem is established. The application uses libxam.dll to store/retrieve “content objects” to/from the XSystem. These “content objects” are bundles of data and metadata, and are called XSets. Intelligent Storage, May 2007
CAS with OSD Archive Catalog Security Manager GigE/App-specific Archive Application OSD Controller XAM library LAN Hosts OSD Drives GigE/OSD Applications use XAM library, XAM VIM translates to OSD protocol and attributes, any OSD device can be a back-end; CAS doesn’t have to have a file system inside Intelligent Storage, May 2007 CAS/XAM replaces “top” of file system, OSD replaces “bottom” of file system SAS/OSD
Scalable NAS with OSD MDS protocol pNFS LAN Hosts File Manager Security Manager OSD Controller OSD IETF pNFS shown here; proprietary alternatives: Lustre/OST or Panasas DirectFLOW SAS/OSD Intelligent Storage, May 2007
XAM Architecture (2) XAM Library XSystem XRI XSet XUID Properties Xstreams 3-levels of objects (hierarchy) • XAM Library: top level object for the XAM API library - Contains methods to get and set fields describing the configuration of the XAM system - Acts as a factory of XSystems • XSystem: object that abstracts the connection between application and storage systems - Encapsulates any resource management associated with the connection - Contains methods used to authenticate operations - Acts as a virtual storage system, partitioning the content • XSet: object that contains application/user data and metadata - Has a globally unique identifier, called XUID (80 bytes) Each level of XAM abstraction (XAM Library, XSystem, XSet) contains “fields” (of type “property” or “xstream”) Intelligent Storage, May 2007
XAM Architecture (3) Two types of Fields: XAM Library XSystem XSet • Properties XRI
XAM to OSD Recommended Mapping Option 1 XAM Library XSystem XSet XRI •XSETs are mapped to collection objects •Properties are mapped to attribute pages •Xstreams are mapped to user objects •XAM names are stored as OSD attributes •OSD provides ways to iterate through these fields •Systems may use external objects for quick XAM name to OID mappings List of member Objects XUID Properties Xstreams List of member Objects C2 C1 P1 Intelligent Storage, May 2007 User UserData UserData U1 UserData U1 Data U1 U1
XAM to OSD Recommended Mapping Option 2 XAM Library XSystem XSet XRI •XSETs are mapped to collection objects •Properties are mapped to user pages •Xstreams are mapped to user objects •XAM names are stored as OSD attributes •OSD provides ways to iterate through these fields •Systems may use external objects for quick XAM name to OID mappings List of member Objects XUID Properties Xstreams List of member Objects C2 C1 P1 Intelligent Storage, May 2007 User UserData UserData U1 UserData U1 Data U1 U1
Ongoing Work XAM Field Attributes • How are they mapped to OSD attributes - Probably define new OSD attributes - (user-defined vs. standards-defined) Mapping of XAM methods to OSD commands Mapping of default fields (Xstreams, properties) to OSD Management Policies • Retention, deletion, storage Jobs • Submit and halt • Query processing - Possible overlap with OSD-2 QUERY command for level 1 queries Intelligent Storage, May 2007
Roadmap XAM to OSD Mapping – ongoing work - Basic object mapping is done, but a lot more details to go… Plan to have a complete document in Summer 2007 - Available to the general public in the form of a White Paper and Best Practices document - Joint FCAS and OSD group work Demonstrate a prototype implementation among group of OSD partners once XAM reference is available Intelligent Storage, May 2007
Backup Slides
Strong LIST (COLLECTION) and Multi-Object Operations in OSD-2
Strong LIST and LIST COLLECTION –Idea: Return some member object attributes along with each OID –Mechanism: - A 1-bit field called “LIST ATTR” is added to CDB - When this bit is set, clients can request member object attributes via the “Get and set attributes parameters” field • Just like they request regular object attributes • OSD uses attribute page numbers to differentiate between container object and member object attributes
Multi-Object Operations (1) –Idea: Execute a single command on multiple objects - Simplicity - Performance –Mechanism: - Can only be issued to “cloned” collection objects • Exception for REMOVE MEMBER OBJECT command
Multi-object Operations (2) –Error Recovery: if a MO operation fails in the middle for any reason, OSD will - Issue no more sub-commands as part of the MO command, - Complete any sub-commands that are currently in-flight, - Fence any objects that have been detected as damaged (possibly multiple objects), - Return an error code for the first damaged object –A client can re-issue the same command after damaged objects have been fixed - Operation will resume and only those objects that have not been operated before will be operated on –If an ABORT TASK is received during the MO operation, OSD will ensure objects are left at a stable state or fenced Intelligent Storage, May 2007
Multi-object Operations (3) –Multi-object operations defined: • • • • QUERY REMOVE MEMBER OBJECTS SET MEMBER ATTRIBUTES GET MEMBER ATTRIBUTES Intelligent Storage, May 2007
Multi-object Operations (4) QUERY Command –Idea: provide a search mechanism for OSD based on attributes - Upon receipt of a QUERY command, OSD returns the list of all objects whose attributes match the specified criteria - E.g., List all objects that were created within a certain time range –Mechanism: - Similar to LIST COLLECTION command - Requested attribute values are specified in the modified “Get and set attributes parameters” field as follows: • • • • Attribute page number Attribute number Minimum value desired Maximum value desired Intelligent Storage, May 2007
Multi-object Operations (5) REMOVE MEMBER OBJECTS Command –Idea: multi-object version of the REMOVE command –Member objects are removed, but not the collection object –Unlike other MO operations, can be issued to a regular collection object Intelligent Storage, May 2007
Multi-object Operations (6) SET MEMBER ATTRIBUTES Command –Idea: multi-object version of SET ATTRIBUTES command –Same attribute values are stored on all the member objects –Attributes are specified in the “Get and set attributes parameters” field - OSD uses attribute page numbers to differentiate between container object and member object attributes Intelligent Storage, May 2007
Multi-object Operations (7) GET MEMBER ATTRIBUTES Command –Idea: multi-object version of GET ATTRIBUTES command –Similar to strong LIST but provides total randomness –Attributes are specified in the “Get and set attributes parameters” field - OSD uses attribute page numbers to differentiate between container object and member object attributes Intelligent Storage, May 2007
Miscellaneous Proposals Approved for OSD-2
Alignment Issue with Attribute Lists Courtesy of Todd Pisek Intelligent Storage, May 2007
64-bit CDB Alignment Issue –There are several 64-bit fields in the CDB that are not aligned at 8 byte boundaries. On a 64-bit Sun SPARC, this is very inconvenient, since attempting to access these fields as 64 bit values will cause an address fault. They have to pull the fields out 32 bits at a time. –The CDB could easily be rearranged (by moving a reserved field) so that all 64 bit values fall on 8 byte boundaries. APPEND: - LENGTH field (offset: 36) CREATE AND WRITE: - LENGTH field (offset: 36) - STARTING BYTE ADDRESS field (offset: 44) FORMAT OSD: - FORMATTED CAPACITY field (offset: 36) LIST: - ALLOCATION LENGTH field (offset: 36) - INITIAL OBJECT_ID field (offset: 44) LIST COLLECTION: - ALLOCATION LENGTH field (offset: 36) - INITIAL OBJECT_ID field (offset: 44) PERFORM TASK MANAGEMENT FUNCTION: - TASK TAG field (offset: 44) (variable length?) READ: - LENGTH field (offset: 36) - STARTING BYTE ADDRESS field (offset: 44) WRITE: Intelligent Storage, May 2007
FC & SAS Issues Resolved –Several requirements in the SCSI OSD standard conflict with the FCP and SAS transport standards. • Fill bytes issue: With the transfer length of buffer segments in bytes, fill bytes may be needed at the end of each segment transfer. - In both FCP and SAS, fill bytes are only allowed on the last frame (highest offset) in each direction per command. • Buffer gaps issue: Unused bytes are not transferred. - In the SCSI architecture, modify data pointer is required to support any out of order transfers. - FCP requires all bytes in the Data-Out and Data-In buffers be transferred. • Modify data pointers are optional but not widely supported. • There is currently a proposal to remove modify data pointers from the standard.
Range-based FLUSH –Purpose: - Update the current FLUSH command to enable clients to specify a range of bytes they wish to flush to permanent storage (useful for large objects). –Mechanism: - Modify the CDB to include the following fields: • Use bytes 32-39 for LENGTH • Use bytes 40-47 for STARTING BYTE ADDRESS
CLEAR Command –Clear is a specialized write operation in which a range in the object content needs to become all ‘0’s. - Purpose: to efficiently make a ‘0’-filled hole in an object (sparse objects) - OSD should support this command, now that it manages the block allocation, to support file clear effectively. –Mechanism: - Define a new CDB for CLEAR that is very similar to the WRITE CDB (new service action code and no user data in the data-out buffer) - Can probably use WRITE permission bit, no need to define a new one. Intelligent Storage, May 2007
PUNCH Command –PUNCH is a specialized write operation similar to CLEAR only that it “zips up” the object to eliminate the hole completely. - For an object of 1024 bytes, if 256 bytes at offset 256 are punched, the new object will have 768 bytes and the bytes formerly at offset 512-1023 are now at 256-767. - This is a logical companion to clear. - Also called “CUT”. - Purpose: to efficiently remove a section of an object –Mechanism: - Define a new CDB for PUNCH that is very similar to the WRITE CDB (new service action code and no user data in the data-out buffer) - Can probably use WRITE permission bit, no need to define a new one. Intelligent Storage, May 2007
Set One Attribute without Data Buffer Intelligent Storage, May 2007
Read Past End of Object Intelligent Storage, May 2007
Reservations Intelligent Storage, May 2007
Security Related Changes in OSD-2
Boot Epoch –What is boot epoch? - Associated with the OSD - Settable by security admin to an arbitrary value - May be incremented by target on reboot • A cyclic value
Changes to Capability capability Sec Info Key Expiry version Time Audit Disc Format Permissions Obj Creation time Obj Type Obj Descriptor doubled doubled Capability Format – more formats Key version x 2 Object created time x 2 Object type x 2 [Object descriptor, Object descriptor type] x 2 Permissions • Duplicate bit vector • More bits for new operations Integrity value calculation, extended to K1 and K2 Intelligent Storage, May 2007 Extends by 32 bytes
Extending integrity value calculation Integrity value calculation extended to two keys K1 – key of source partition K2 – key of destination partition Goal: Capability key depending on K1 AND K2 temp_key = HMAC(K1, capability) capability_key = HMAC(K2, temp_key) command_integrity_value = HMAC(capability_key, CDB) Intelligent Storage, May 2007
Range Capabilities Objective • Restrict capability to a given range within the object Two additional fields (8 bytes each) • STARTING_BYTE_OFFSET • LENGTH Applicable for user-object and the following commands: • Create_and_write, Write, Read, Append Enforcement • CDB range must be within the capability range • Appended data should not exceed capability range Intelligent Storage, May 2007
Capabilities for Specific Attributes Support finer grain protection over attributes • Specify in capability which attributes it protects Assumption: • Small # of subsets of attributes to protect • Subsets are relatively static Mechanism • Define a user-defined page P • Specify the page number P in a new capability field - ALLOWED_ATTR_PAGE • P is a list of [attr_page, attr_number] - Allow syntax for [attr_page, *] Enforcement • All attributes accessed by command must be listed in the page Intelligent Storage, May 2007
Exception Management
Exception Management Atomicity –Atomicity is roughly the guarantee that all of a command’s effects are either completely committed w/in the OSD or none of a commands effects are seen within the OSD. In other words; - either all data is written or no data is written - either all attributes are updated or no attributes are updated –Atomicity can occur on data, attributes or both - Controlled by atomicity size • D-limit: maximum amount of data that is guaranteed to be written atomically • A-limit: maximum amount of user-settable attributes that are guaranteed to be written atomically • C-limit: maximum amount of data PLUS user-settable attributes that are guaranteed to be written atomically
Exception Management Isolation – Changes made by one operation are not visible to other simultaneous operations on the system until its completion - – Avoids data from two writes becoming intermingled Avoids attributes from two setattr becoming intermingled Possible solutions 1) Strong isolation – Isolate between commands (only needs to be done on a per-object basis) 2) Weak isolation – Isolate between command phases (e.g., no two commands in the data-phase can modify an object at the same time) – Can be relaxed by implementation if data regions are non overlapping 3) No isolation Intelligent Storage, May 2007
Exception Management Misc. –New Command: OSD FSCK - To fix FS issues that cannot be fixed by outside world –New Command: READ MAP - Returns a map of the object indicating DATA, DAMAGED, and HOLE sections of the object. –Media Error Handling - Damage discovery, handling, and reporting Intelligent Storage, May 2007
