News Column

Researchers Submit Patent Application, "Valid Page Threshold Based Garbage Collection for Solid State Drive", for Approval

February 20, 2014



By a News Reporter-Staff News Editor at Computer Weekly News -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Bux, Werner (Richterswil, CH); Haas, Robert (Ossining, NY); Hu, Xiao-Yu (Horgen, CH); Iliadis, Ilias (Rueschlikon, CH), filed on July 27, 2012, was made available online on February 6, 2014.

The patent's assignee is International Business Machines Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "This disclosure relates generally to computer memory devices, and more particularly to garbage collection in a solid state drive (SSD).

"SSDs, which include flash memory devices, are rewritable non-volatile memory devices that use electronic circuitry for storing data. SSDs may be used for many types of computer memory, for example, local computer hard drives, peripheral storage, or storage for enterprise applications. SSDs offer relatively good bandwidth and random I/O (input/output) performance along with a relatively good lifespan due to an absence of moving parts.

"SSD memory is organized in memory blocks. Each block includes a plurality of pages (a page is a relatively small unit of memory). Read and write operations in a SSD may be performed at the page level; however, erase operations may only be performed at the memory block level. Erase operations may also take more time to complete than read or write operations. In order to overwrite data (i.e., replace old data with updated data) that is stored in a memory block in a SSD, an erase operation of the entire memory block that holds the data to be overwritten must be performed. In order to overwrite data in a SSD, a writing technique referred to as 'write out of place' may be applied, in which the updated data is written to a free (i.e., empty) page in the SSD memory instead of writing the updated data to the same page where old data resides. The page containing the old data is then marked as invalid page. An invalid page remains invalid until the entire memory block in which the invalid page is located is erased.

"During operation of the SSD, garbage collection is performed to maintain a free block pool. The free block pool holds memory blocks that contain free pages that are available for writing new data. The free blocks are reclaimed from memory blocks that may be filled with both valid and invalid data. The garbage collection process first identifies a victim block for reclaiming. Any valid pages (i.e., pages containing data that has not been overwritten) residing in the victim block are copied to another memory block, and the victim block is erased, such that the entire victim block is now a free block for the free block pool. The garbage collection process requires read and write operations, in addition to the erase operation, that may compete with regular user read and write operations for access to the same memory and controller resources. Overly frequent garbage collection may increase write amplification in the SSD, which may increase the power consumption of the SSD and eventually decrease the lifespan of the SSD."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "In one aspect, a method for garbage collection in a SSD includes determining whether the SSD is idle by a garbage collection module of the SSD; based on determining that the SSD is idle, determining a victim block from a plurality of memory blocks of the SSD; determining a number of valid pages in the victim block; comparing the determined number of valid pages in the victim block to a valid page threshold; and based on the number of valid pages in the victim block being less than the valid page threshold, issuing a garbage collection request for the victim block.

"In another aspect, a SSD includes a plurality of memory blocks, each of the plurality of memory blocks comprising a respective plurality of pages; and a SSD controller, the SSD controller comprising a garbage collection module, the garbage collection module being configured to perform a method including determining whether the SSD is idle; based on determining that the SSD is idle, determining a victim block from the plurality of memory blocks; determining a number of valid pages in the victim block; comparing the determined number of valid pages in the victim block to a valid page threshold; and based on the number of valid pages in the victim block being less than the valid page threshold, issuing a garbage collection request for the victim block.

"Additional features are realized through the techniques of the present exemplary embodiment. Other embodiments are described in detail herein and are considered a part of what is claimed. For a better understanding of the features of the exemplary embodiment, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

"Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:

"FIG. 1 is a schematic block illustrating an embodiment of a SSD including valid page threshold based garbage collection.

"FIG. 2 is a flowchart illustrating an embodiment of a method for valid page threshold based garbage collection for a SSD.

"FIG. 3 is a schematic block illustrating an embodiment of a computer that may be used in conjunction with a SSD including page threshold based garbage collection."

For additional information on this patent application, see: Bux, Werner; Haas, Robert; Hu, Xiao-Yu; Iliadis, Ilias. Valid Page Threshold Based Garbage Collection for Solid State Drive. Filed July 27, 2012 and posted February 6, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=571&p=12&f=G&l=50&d=PG01&S1=20140130.PD.&OS=PD/20140130&RS=PD/20140130

Keywords for this news article include: International Business Machines Corporation.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Computer Weekly News


Story Tools