a cost effective high bandwidth storage architecture n.
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  1. A COST-EFFECTIVEHIGH-BANDWIDTHSTORAGE ARCHITECTURE G.A. Gibson, D. F. Nagle, K. Amiri, J. Butler, F.W. Chang, H. Gobioff,C. Hardin, E. Riedel , D. Rochberg, J. Zelenka Carnegie-Mellon U. ASPLOS ‘98

  2. Paper highlights • Introduces Network-Attached Secure Disk architecture characterized by: • Direct transfers to clients • Secure interfaces via cryptographical support • Asynchronous non-critical path oversight(client can perform most operations us without synchronous appeals to file manager) • Variably-sized data objects

  3. Motivation • High demand for storage bandwidth caused by • Multimedia applications • Data intensive applications such as data mining • Want to achieve scalable bandwidth • Bandwidth that grows linearly with number of storage devices and client processors

  4. Computer Disk Storage architecture overview (I) • Local file system : • Sole solution for stand-alone computers

  5. Storage architecture overview (II) 2. Distributed FS: • Provides basic file services • If server processes data for clients, we have a Distributed Database System • Server machine could become bottleneck when the number of drives increases Client Server Disk

  6. Storage architecture overview (III) • Distributed FS with RAID Controller : • Improves reliability but adds one more layer Client Server K Disk

  7. Storage architecture overview (IV) 4. Distributed FS with DMA: • Lets disks and clients exchange data w/o server intervention Client Server K Disk Bulk data transfers

  8. Storage architecture overview (V) • Network-Attached Secure Disk: • Disk takes over several of the functions of the server Client Server NASD R/W

  9. Storage architecture overview (VI) • Network-Attached Secure Diskwith Cheops(their own file striping system) Client Server K NASD R/W

  10. Related works • Disk-like network attached storage (Cambridge’s Universal File System, 1980) • Virtual volumes and virtual disks (mid 90’s) • Derived Virtual Devices (ISI’s Netstation, 1996) • Capabilities (1966)

  11. Enabling technology (I) • I/O-bound applications:multimedia, data mining of retail transactions • New drive attachment technologies: tendency to encapsulate drive communication over a serial switched packet-based SAN • Excess of on-drive transistors:can now have more intelligent drives

  12. Enabling technology (II) • Convergence of peripheral and interprocessor networks: • Clusters of workstations use Internet protocols • Not special-purpose interconnects • Cost-ineffective storage servers: • Server now much more expensive that the disks it manages

  13. Network-Attached Secure Disks • Modify storage devices to transfer datadirectly to clients • Eliminate server bottleneck • Present a flat-name space of variable length objects • Simple yet flexible • Do not provide full file system functionality • Other FS tasks left to file manager

  14. One way to look at NASD • Conventional architectures divide file system tasks between • A metadata service (directories and i-nodes) • A block storage service • The authors propose to • Let storage units handle block allocation • Let them communicate directly with clients

  15. Network-Attached Secure Disks • Architecture characterized by: • Direct transfers to clients • Secure interfaces via cryptographic support • Asynchronous non-critical path oversight • Client can perform most operations without synchronous calls to file manager • Variable length objects

  16. A NASD System

  17. NASD interface (I) • Less than 20 requests including: • Read and write object data • Read and write object attributes • Create and remove object • Create, resize, and remove partition • Construct a copy-on-write object version • Set security key

  18. NASD interface (II) • Resizable partitions allow capacity quotas to be managed by a drive administrator • Objects with well-known names and structures allow configuration and bootstrap of drives and partitions. • Also enable file systems to find a fixed starting point for an object hierarchy and a complete list of allocated object names

  19. NASD interface (III) • Object attributes • Provide timestamps, size, … • Allow capacity to be reserved and objects to be linked for clustering • Include an uninterpreted block of attribute space • Can be used by any application

  20. NASD interface (IV) • NASD security is based on cryptographic capabilities • Drive checks that client has proivate apt of capability authorizing operation • Data integrity and privacy ensured through encryption • Costly but expected to be implemented on special hardware

  21. Prototype implementation (I) • Working prototype of the NASD drive software runs as a kernel module in Digital UNIX • Each NASD prototype drive runs on a DECAlpha3000/400 (133MHz, 64MB) with two disks attached by two 5MB/s SCSI busses • Performance of this old machine is similar to that expected from future drive controllers

  22. Prototype implementation (II) • Two drives managed by a software striping driver approximate the rates expected from more modern drives • NASD object system implements its own internal object access, cache, and disk space management • Prototype uses DCE RPC over UDP/IP for communication • Severely limited prototype performance

  23. File Systems for NASD (I) • Implemented NFS and AFS on top of simulated NASDs • Files and directories stored as objects • NFS implementation was straightforward • Can store additional file attributes in uninterpreted block of attribute space • Can piggyback capabilities on file manager’s response to lookup requests

  24. File Systems for NASD (II) • AFS implementation required more thought • New RPC calls were added to obtain and relinquish capabilities • File manager does not know when an actual write takes place • Replaced callbacks by leases • NASD-NFS and NFS had benchmark times “within 5% of each other”

  25. File Systems for NASD (III) • Also implemented a simple parallel file system not discussed in class

  26. Conclusions • NASD • Supports direct device-to-client operation • Provides secure interfaces • Lets file managers provide clients with capabilities that allow them to interact directly with the devices (asynchronous oversight) • Lets devices serve variable-length objects with additional attribures