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DADA – Dynamic Allocation of Disk Area

DADA – Dynamic Allocation of Disk Area. Jayaram Bobba Vivek Shrivastava. Outline. Introduction Existing Framework Implementation Issues Results Conclusions. Problem. Disk Volumes Allocate physical space on creation Multiple Disk Volumes on a physical disk Unused space

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DADA – Dynamic Allocation of Disk Area

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  1. DADA – Dynamic Allocation of Disk Area Jayaram Bobba Vivek Shrivastava Department of Computer Sciences, University of Wisconsin Madison

  2. Outline • Introduction • Existing Framework • Implementation • Issues • Results • Conclusions Department of Computer Sciences, University of Wisconsin Madison

  3. Problem • Disk Volumes • Allocate physical space on creation • Multiple Disk Volumes on a physical disk • Unused space • Disk space not a premium • What If? Department of Computer Sciences, University of Wisconsin Madison

  4. Motivation • Virtual Machine Environment • Multiple OS may create pressure on disk space • Access patterns may warrant dynamic relocation of disk blocks • Storage Area Networks • Storage area is a bottleneck resource • Dynamic Physical Allocation (LFS style) • Group writes from various volumes into a single physical write. Department of Computer Sciences, University of Wisconsin Madison

  5. Related Work • HP AutoRAID • Dynamically change redundancy levels • Hot Data – Mirrored • Cold Data – RAID 5 • Dynamic migration of data Department of Computer Sciences, University of Wisconsin Madison

  6. Outline • Introduction • Existing Framework • Implementation • Issues • Results • Conclusions Department of Computer Sciences, University of Wisconsin Madison

  7. Existing Framework • Logical Volume Manager (LVM) • User space tool that enables creation of logical volumes of a logical partition. • Supports resizing of volumes. • Device Mapper (DM) • Kernel driver that provides a level of indirection in address translation Department of Computer Sciences, University of Wisconsin Madison

  8. LVM design • Physical Volume (PV) • Volume Group (VG) • Logical Volume (LV) • Physical Extent (PE) • Logical Extent (LE) Department of Computer Sciences, University of Wisconsin Madison

  9. LVM design Physical Device Department of Computer Sciences, University of Wisconsin Madison

  10. LVM design PV PE Department of Computer Sciences, University of Wisconsin Madison

  11. LVM design LV 1 PV PE Department of Computer Sciences, University of Wisconsin Madison

  12. LVM design LE LV 1 LV2 PV PE Department of Computer Sciences, University of Wisconsin Madison

  13. LVM design LE LV 1 LV2 PV PE Department of Computer Sciences, University of Wisconsin Madison

  14. LVM design LE VG LV 1 LV2 PV PE Department of Computer Sciences, University of Wisconsin Madison

  15. LVM – DM interaction LVM2 libdevmapper Userspace Kernel Device Mapper Department of Computer Sciences, University of Wisconsin Madison

  16. Outline • Introduction • Existing Framework • Implementation • Issues • Results • Conclusions Department of Computer Sciences, University of Wisconsin Madison

  17. Modifications • A trap mechanism from kernel driver to user-level LVM code. • Support for multiple segments in LV • Support for virtual mappings in driver Department of Computer Sciences, University of Wisconsin Madison

  18. Initial State LVM daemon LVM User space Kernel space Device Mapper Unallocated Disk Space Department of Computer Sciences, University of Wisconsin Madison

  19. Volume Group Creation LVM daemon LVM User space Kernel space Device Mapper PE (4MB) 25 Extents Unallocated Disk Space Department of Computer Sciences, University of Wisconsin Madison

  20. Current Implementation LVM daemon Create LV 32MB User A LVM User space Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  21. Current Implementation LVM daemon User A LVM Map 0-7 extents for user A User space Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  22. Current Implementation LVM daemon User A LVM Map 0-7 extents for user A User space Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  23. Current Implementation LVM daemon User A LVM Create LV User B 16 MB User space Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  24. Current Implementation LVM daemon User A LVM Create LV User B 16 MB map 8-11 extents for B User space Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  25. Current Implementation LVM daemon User A LVM User B map 8-11 extents for B User space Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  26. Current Implementation LVM daemon User A LVM User B Read/write User space Read/write Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  27. Volume Group Creation LVM daemon LVM User space Kernel space Device Mapper PE (4MB) 25 Extents Unallocated Disk Space Department of Computer Sciences, University of Wisconsin Madison

  28. Modified Implementation LVM daemon Create LV1 32MB User A LVM User space Kernel space Device Mapper Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  29. Modified Implementation LVM daemon User A LVM Virtually map 0-7 extents for user A User space Kernel space Device Mapper {0-7 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  30. Modified Implementation LVM daemon User A LVM Create LV User B 16 MB User space Kernel space Device Mapper {LV A 0-7 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  31. Modified Implementation LVM daemon User A LVM Create LV2 User B 16 MB Virtually map 0-3 extents for B User space Kernel space Device Mapper {LV A 0-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  32. Modified Implementation LVM daemon User A LVM Write 6MB User B User space Kernel space Device Mapper {LV A 0-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  33. Modified Implementation LVM daemon User A LVM Write 6MB User B trap User space Kernel space Device Mapper {LV A 0-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  34. Modified Implementation On Demand allocation of disk area LVM daemon User A LVM Write 6MB User B trap User space Kernel space Device Mapper {LV A 0-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  35. Modified Implementation On Demand allocation of disk area LVM daemon User A LVM Write 6MB User B Allocate 0-1 extents (8MB) LV A User space Kernel space Device Mapper {LV A 0-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  36. Modified Implementation On Demand allocation of disk area LVM daemon User A LVM Write 6MB User B Return User space Kernel space Device Mapper {LV A 0-1 linear,2-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  37. Modified Implementation LVM daemon User A LVM User B Write 10MB User space Kernel space Device Mapper {LV A 0-1 linear,2-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  38. Modified Implementation LVM daemon User A LVM User B Write 10 MB trap User space Kernel space Device Mapper {LV A 0-1 linear,2-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  39. Modified Implementation On Demand allocation of disk area LVM daemon User A LVM User B Write 10 MB trap User space Kernel space Device Mapper {LV A 0-1 linear,2-7 error} {LV B 0-3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  40. Modified Implementation On Demand allocation of disk area LVM daemon User A LVM User B LV B Allocate 8-11 extents (12 MB) Write 10 MB User space Kernel space Device Mapper {LV A 0-1 linear,2-7 error} {LV B 0-2 linear, 3 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  41. Outline • Introduction • Existing Framework • Implementation • Issues • Results • Conclusions Department of Computer Sciences, University of Wisconsin Madison

  42. Issues LVM implementation not efficient LVM2 libdevmapper Userspace Kernel Device Mapper Department of Computer Sciences, University of Wisconsin Madison

  43. Issues LVM implementation not efficient LVM2 Costly kernel-user space crossing libdevmapper Userspace Kernel Device Mapper Department of Computer Sciences, University of Wisconsin Madison

  44. Issues LVM implementation not efficient LVM2 Normal function call libdevmapper Userspace Device Mapper Kernel Department of Computer Sciences, University of Wisconsin Madison

  45. More Issues • On a trap • How much to allocate? • On demand • Pre-allocate • Where to allocate? • Temporal locality • Spatial locality • Free unused space Department of Computer Sciences, University of Wisconsin Madison

  46. How much? • On-demand • Allocate only as many blocks as needed • Pre-allocate • Pre-allocate physical space for blocks likely to be accessed in the future. • How much? • Where? Department of Computer Sciences, University of Wisconsin Madison

  47. How much? • Tradeoff – Performance vs. Disk Space • Depends on the workload • I/O on critical path • Asynchronous I/O • Multithreaded Applications Department of Computer Sciences, University of Wisconsin Madison

  48. Pre-Allocation Think: Filesystem Block Allocation • Dumb Allocation • Stride Allocation • Multi-Strided Allocation Department of Computer Sciences, University of Wisconsin Madison

  49. Allocation Strategy On Demand allocation of disk area LVM daemon User A LVM Write Allocate 2 extents (8MB) trap User space Kernel space Device Mapper {0-1 linear}{2-7 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

  50. Allocation Strategy On Demand allocation of disk area LVM daemon User A LVM Write Allocate 2 extents (8MB) trap User space Kernel space Device Mapper {0-1 linear}{2-7 error} Free Disk Space Department of Computer Sciences, University of Wisconsin Madison

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