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Researchers Submit Patent Application, "Rebuild of Redundant Secondary Storage Cache", for Approval

September 2, 2014



By a News Reporter-Staff News Editor at Information Technology Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Biswas, Sujan (Kolkata, IN); Sheik, Karimulla (Bangalore, IN); Samanta, Sumanesh (Bangalore, IN); Mridha, Debal K. (Bangalore, IN); Vadalamani, Naga S. (Bangalore, IN), filed on February 11, 2013, was made available online on August 21, 2014.

The patent's assignee is LSI Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "Local solid state drive (SSD) caching can be used for secondary caching in storage architectures. Secondary caching devices in these configurations are typically redundant in order to reliably cache 'dirty' data (e.g., data in a secondary cache that does reflect the contents of primary storage). When a redundant drive fails, however, a rebuild operation of the redundant drives can be complex and time consuming, because the same device can be caching data for different source Virtual Drives (VDs). An SSD volume may be rebuilt relatively easily offline with no background input/output (IO) being executed. However, this technique requires keeping the IO system offline for an extended time and is not suited for practical use cases that involve mission critical data, always 'on' systems, and so forth. A technique to avoid rebuild is to remove dirty data (e.g., flush dirty data from SSD cache to primary storage) from a surviving drive so that the data is not exchanged for rebuild. Once the dirty data has been removed (flushed), redundant storage of dirty data can be performed for subsequent write IOs. However, with SSDs having large storage capacities (e.g., on the order of terabytes of data), flushing dirty data to disk is highly time consuming and detrimental to performance, since new WRITE cache (dirty data generation) cannot restart unless the entirety of the dirty data is flushed to disk. This can be especially problematic in configurations where data is mirrored across multiple servers, e.g., where the entire dirty cache needs to be flushed every time a server is rebooted, even when a mirrored drive is absent from the storage system for only a small amount of time (as the corresponding server is rebooted)."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "System and techniques for rebuilding a redundant secondary storage cache including a first storage device and a second storage device are described. A metadata entry indicative of a validity of a portion of information stored by a first storage cache device and associated with a region of a primary storage device is received. When the validity of the portion of information associated with the region of the primary storage device is established, a region lock is requested on the region of the primary storage device associated with the portion of information stored by the first storage cache device. Then, the portion of information and the corresponding metadata entry associated with the region of the primary storage device are copied from the first cache storage device to a second storage cache device to rebuild the second storage cache device. In embodiments, a watermark is maintained signifying the level to which rebuild is done. IO above the watermark is cached and treated as if hitting redundant online secondary cache.

"This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features 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.

BRIEF DESCRIPTION OF THE FIGURES

"Other embodiments of the disclosure will become apparent.

"FIG. 1 is a block diagram illustrating a system that provides primary data storage to clients, where the system implements a redundant secondary storage cache in accordance with example embodiments of the present disclosure.

"FIG. 2 is a block diagram illustrating a single controller for a data storage system that implements a redundant secondary storage cache, such as the system illustrated in FIG. 1, in accordance with example embodiments of the present disclosure.

"FIG. 3 is a block diagram illustrating two controllers for a data storage system that implements a redundant secondary storage cache, such as the system illustrated in FIG. 1, where a first controller is connected to a second controller to implement mirroring of write back data in accordance with example embodiments of the present disclosure.

"FIG. 4 is a flow diagram illustrating a method for rebuilding a secondary storage cache in a system that provides primary data storage to clients in accordance with example embodiments of the present disclosure."

For additional information on this patent application, see: Biswas, Sujan; Sheik, Karimulla; Samanta, Sumanesh; Mridha, Debal K.; Vadalamani, Naga S. Rebuild of Redundant Secondary Storage Cache. Filed February 11, 2013 and posted August 21, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=438&p=9&f=G&l=50&d=PG01&S1=20140814.PD.&OS=PD/20140814&RS=PD/20140814

Keywords for this news article include: LSI Corporation, Information Technology, Information and Data Storage.

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Source: Information Technology Newsweekly


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