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GCTrees: Garbage Collecting Snapshots

GCTrees: Garbage Collecting Snapshots GCTrees: Garbage Collecting Snapshots CHRIS DRAGGA and DOUGLAS J. SANTRY, Advanced Technology Group, NetApp Inc. File-system snapshots have been a key component of enterprise storage management since their inception. Creating and managing them efficiently, while maintaining flexibility and low overhead, has been a constant struggle. Although the current state-of-the-art mechanism--hierarchical reference counting--performs reasonably well for traditional small-file workloads, these workloads are increasingly vanishing from the enterprise data center, replaced instead with virtual machine and database workloads. These workloads center around a few very large files, violating the assumptions that allow hierarchical reference counting to operate efficiently. To better cope with these workloads, we introduce Generational Chain Trees (GCTrees), a novel method of space management that uses concepts of block lineage across snapshots rather than explicit reference counting. As a proof of concept, we create a prototype file system--gcext4, a modified version of ext4 that uses GCTrees as a basis for snapshots and copy-on-write. In evaluating this prototype empirically, we find that although they have a somewhat higher overhead for traditional workloads, GCTrees have dramatically lower overhead than hierarchical reference counting for large-file workloads, improving by a factor of 34 or more in some cases. Furthermore, gcext4 performs comparably http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png ACM Transactions on Storage (TOS) Association for Computing Machinery

GCTrees: Garbage Collecting Snapshots

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Publisher
Association for Computing Machinery
Copyright
Copyright © 2016 by ACM Inc.
ISSN
1553-3077
DOI
10.1145/2857056
Publisher site
See Article on Publisher Site

Abstract

GCTrees: Garbage Collecting Snapshots CHRIS DRAGGA and DOUGLAS J. SANTRY, Advanced Technology Group, NetApp Inc. File-system snapshots have been a key component of enterprise storage management since their inception. Creating and managing them efficiently, while maintaining flexibility and low overhead, has been a constant struggle. Although the current state-of-the-art mechanism--hierarchical reference counting--performs reasonably well for traditional small-file workloads, these workloads are increasingly vanishing from the enterprise data center, replaced instead with virtual machine and database workloads. These workloads center around a few very large files, violating the assumptions that allow hierarchical reference counting to operate efficiently. To better cope with these workloads, we introduce Generational Chain Trees (GCTrees), a novel method of space management that uses concepts of block lineage across snapshots rather than explicit reference counting. As a proof of concept, we create a prototype file system--gcext4, a modified version of ext4 that uses GCTrees as a basis for snapshots and copy-on-write. In evaluating this prototype empirically, we find that although they have a somewhat higher overhead for traditional workloads, GCTrees have dramatically lower overhead than hierarchical reference counting for large-file workloads, improving by a factor of 34 or more in some cases. Furthermore, gcext4 performs comparably

Journal

ACM Transactions on Storage (TOS)Association for Computing Machinery

Published: Jan 28, 2016

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