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A new method of SSD GC based on Key Factor Decision

IP.com Disclosure Number: IPCOM000248247D
Publication Date: 2016-Nov-11
Document File: 6 page(s) / 136K

Publishing Venue

The IP.com Prior Art Database

Abstract

This disclosure introduces a new method of SSD GC(garbage collection of Solid State Drive). The main idea is to select the best block for GC by using key factor decision no matter BGC or PGC. It will decelerate wear off and decrease unnecessary cost of free page operation. Meanwhile, the method can increase GC efficiency.

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Page 01 of 6

A new method of SSD GC based on Key Factor Decision

In general, read and write of SSD (Solid State Drive) follow three rules. Firstly, the minimum unit of read and write is page, the minimum unit of erase is block. Secondly, Erase is required before write. Thirdly, data can't be overridden. If the data in some of the pages of the block are no longer needed (also called stale pages), only the pages with good data in that block are read and rewritten into another previously erased empty block. Then the free pages left by not moving the stale data are available for new data. This is a process called SSD GC (garbage collection of Solid State Drive).

For example, block x has valid pages (A, B, C) and other pages are invalid, block y has valid pages (D, E, F, G) and other pages are invalid. GC will first search a new block z, then move pages (A, B, C, D, E, F, G)to block z. Next, block x and block y will be erased and turn to new available blocks.

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Page 02 of 6

Picture-1 The process of GC


Currently there are two kinds of SSD GC. The first method is background garbage collection(BGC), where SSD controller use idle time to do GC. The second one is parallel garbage collection(PGC), where SSD controller do GC during IO. Both of above two methods can free space, but wear increases accordingly. Some blocks with high fatigue wear are erased frequently, which decrease blocks' endurance.

This disclosure introduces a new method of SSD GC. The main idea is to select the best block for GC by using key factor decision no matter BGC or PGC.


1. Key Factor Decision(KFD)

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Page 03 of 6

This is a method integrated in firmware of SSD controller, which will generate a rank of blocks and send the best one to GC. SSD controller can mon...