News Column

Patent Issued for Efficient File System Metadata Scanning Using Scoped Snapshots

May 13, 2014

By a News Reporter-Staff News Editor at Information Technology Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Havewala, Sarosh C. (Kirkland, WA); Christiansen, Neal R. (Bellevue, WA); Haury, Lane (Kirkland, WA), filed on September 21, 2011, was published online on April 29, 2014.

The assignee for this patent, patent number 8713270, is Microsoft Corporation (Redmond, WA).

Reporters obtained the following quote from the background information supplied by the inventors: "File systems utilize data structures, also referred to as the file system on-disk format, to persist, i.e., maintain and organize, data to stable storage, e.g., a volume, disk, hard drive, etc. File systems access the data and interpret these data structures to store and retrieve data for users and applications, or procedures or computer programs, e.g., when executing software instructions or computer code.

"Error scanning is performed for the volumes of a file system in order to proactively identify corruptions in their data structures. A proactive error scanning process involves generating snapshots for volumes of the file system and performing actions on the data structures in the volume snapshots to identify existing corruptions. In embodiments the proactive error scanning process executes while the file system volumes remain online and, therefore, accessible to other users and applications.

"However, there are issues introduced by the proactive error scanning process' use of a volume snapshot. For example, the copy-on-write mechanism typically employed to generate and maintain the snapshot view of a volume is expensive in terms of I/O, i.e., input/output, processing costs. This in turn imposes performance penalties on the I/O that applications are attempting to perform with the underlying real volume while the proactive error scanner uses the volume snapshot.

"Moreover, as applications perform I/O operations on the real volume during proactive error scanning the copy-on-write mechanism saves the changed data blocks away into a difference, i.e., diff, area on the volume. As the number of changed data blocks grows the volume space required for the diff area increases. This can negatively impact overall file system performance as it has increasingly less free volume space for application usage. Too, if the diff area becomes too large older snapshots will have to be deleted to make room for the newer changed blocks. In some cases, the snapshot used by the proactive error scanner may itself have to be deleted and the proactive error scanner will have to be prematurely terminated and then subsequently restarted again from the beginning, utilizing valuable system time and resources.

"Thus it is desirable to minimize, i.e., scope, the snapshot of the volume used by the proactive error scanner to those sections of the volume that are actually utilized by the proactive error scanner. It is further desirable to determine the scope of the volume snapshot for use by proactive error scanner in a timely manner in order to further minimize volume error detection processing effects on the file system's performance and resources."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "This summary is provided to introduce a selection of concepts in a simplified form which are further described below in the Detailed Description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

"Embodiments discussed herein include systems and methodology for determining for a file system volume that is undergoing proactive error scanning while the volume is online and available to other applications and users those volume clusters that are to be snapshotted during the entire proactive error scanning process. In an embodiment proactive error scanning is performed on a volume to determine if the volume has any corruptions. In an embodiment proactive error scanner processing need only reference file system metadata to perform its functionality. Thus, in an embodiment an entire volume, i.e., user data and unused volume clusters, need not be snapshotted for the duration of proactive error scanner processing.

"In an embodiment a volume undergoing proactive error scanner processing is snapshotted in its entirety during a first, nominal time processing, phase to ensure the volume's file system metadata can be relied on to accurately identify the file system metadata on the volume. In an embodiment, during subsequent phases when the proactive error scanner is actively processing the file system metadata of a volume scanning for corruptions, only those volume clusters containing file system metadata continue to be snapshotted.

"In an embodiment during the first proactive error scanner processing phase a snapshot bitmap is generated and populated that identifies the volume clusters that contain file system metadata, and thus are to continue to be snapshotted for the duration of proactive error scanner processing on the volume. In this embodiment the generated snapshot bitmap also, de facto, identifies the volume clusters that contain user data or are currently free, i.e., contain no meaningful data, and thus do not need to continue to be snapshotted for the remainder, i.e., any subsequent phases, of proactive error scanner processing on the volume."

For more information, see this patent: Havewala, Sarosh C.; Christiansen, Neal R.; Haury, Lane. Efficient File System Metadata Scanning Using Scoped Snapshots. U.S. Patent Number 8713270, filed September 21, 2011, and published online on April 29, 2014. Patent URL:

Keywords for this news article include: Microsoft Corporation, Information Technology, Information and Data Architecture.

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Source: Information Technology Newsweekly

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