Selfie: Co-locating metadata and data to enable fast virtual block devices

Xingbo Wu, Zili Shao, Song Jiang

Research output: Chapter in book / Conference proceedingConference article published in proceeding or bookAcademic researchpeer-review

8 Citations (Scopus)


Virtual block devices are widely used to provide block inter- face to virtual machines (VMs). A virtual block device man- Ages an indirection mapping from the virtual address space presented to a VM, to a storage image hosted on file system or storage volume. This indirection is recorded as metadata on the image, also known as a lookup table, which needs to be immediately updated upon each space allocation on the image for data safety (also known as image growth). This growth is common as VM templates for large-scale deploy- ments and snapshots for fast migration of VMs are heavily used. Though each table update involves only a few bytes of data, it demands a random write of an entire block. Further- more, data consistency demands correct order of metadata and data writes be enforced, usually by inserting the FLUSH command between them. These metadata operations com- promise virtual device's efficiency. In this paper we introduce Selfie, a virtual disk for- mat, that eliminates frequent metadata writes by embedding metadata into data blocks and makes write of a data block and its associated metadata be completed in one atomic block operation. This is made possible by opportunistically compressing data in a block to make room for the metadata. Experiments show that Selfie gains as much as 5x perfor- mance improvements over existing mainstream virtual disks. It delivers near-raw performance with an impressive scala- bility for concurrent I/O workloads.
Original languageEnglish
Title of host publicationSYSTOR 2015 - Proceedings of the 8th ACM International Systems and Storage Conference
PublisherAssociation for Computing Machinery, Inc
ISBN (Electronic)9781450336079
Publication statusPublished - 26 May 2015
Event8th ACM International Systems and Storage Conference, SYSTOR 2015 - Haifa, Israel
Duration: 26 May 201528 May 2015


Conference8th ACM International Systems and Storage Conference, SYSTOR 2015

ASJC Scopus subject areas

  • Software
  • Electrical and Electronic Engineering
  • Hardware and Architecture
  • Computer Science Applications


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