NDLI: iROW: An Efficient Live Snapshot System for Virtual Machine Disk

Content Provider	IEEE Xplore Digital Library
Author	Jianxin Li Hanqing Liu Lei Cui Bo Li Tianyu Wo
Copyright Year	2012
Abstract	The high-availiablity of mission-critical data and services hosted in a virtual machine (VM) is one of the top concerns in a cloud computing environment. The live disk snapshot is an emerging technology to save the whole state and the data of a VM at a specific point of time, and be used for quick disaster recovery. However, the existing VM disk snapshot systems suffer from long operation time and I/O performance degradation problems during snapshots creating and managing, and thereby affecting the performance of the VM and its services. To address such issues, we designed an efficient VM disk snapshot system, named iROW (improved Redirect-on-Write). In iROW, a bitmap based light-weight index scheme is adopted to replace the existing multi-level index tree structure to reduce query cost. Additionally, through a combination of Redirect-on-Write (ROW) and Copy-on-Demand (COD) schema to avoid extra copy operation on the first write after snapshot with Copy-on-Write (COW) schema, and the file fragmentation problem caused by ROW snapshot after long-term using. Finally, iROW gives a unified disk space allocation function by the host machine's file system. We have implemented iROW in qemu-kvm 0.12.5 and conducted some experiments. The implementation of iROW completely obey the interfaces of the block device driver in QEMU, so it is transparent to the upper system or applications and original disk image formats can be also supported. The experimental results show that iROW has obvious performance advantages in snapshot creating and management operations. Compared with the existing qcow2 disk image in KVM, when the VM disk size is 50GB, and the cluster size is 64KB (the default cluster size of qcow2), the snapshot creation and rollback time is only about 6% and 3% of original qcow2's. With the increasing of the VM disk size, iROW has more performance advantages on snapshot creation and rollback operations. In addition, the I/O performance of iROW is better than qcow2. When the cluster size is 64 KB, typically the iROW's performance loss is 10% less than qcow2's, and its first write performance after snapshot creation is about 250% of qcow2's.
Starting Page	376
Ending Page	383
File Size	730622
Page Count	8
File Format	PDF
ISBN	9781467345651
ISSN	15219097
e-ISBN	9780769549033
DOI	10.1109/ICPADS.2012.59
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2012-12-17
Publisher Place	Singapore
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Indexes File systems Virtual machining Performance evaluation Reliability Computers Degradation Virtual Disk Image Cloud Computing Virtual Machine Snapshot
Content Type	Text
Resource Type	Article
Subject	Hardware and Architecture

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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