Biasing for wear leveling in storage systems

Patent metadata

Field	Value
Publication number	US-9298608-B2
Application number	US-201314137440-A
Country	US
Kind code	B2
Filing date	Dec 20, 2013
Priority date	Oct 18, 2013
Publication date	Mar 29, 2016
Grant date	Mar 29, 2016

Abstract

The various implementations described herein include systems, methods and/or devices used to enable biasing for wear leveling in storage systems. In one aspect, the method includes (1) determining, for each erase unit of a plurality of erase units in the storage medium, an age metric, (2) determining a representative age metric of the plurality of erase units, (3) for each respective erase unit of the plurality of erase units, biasing a respective garbage collection control metric for the respective erase unit in accordance with the age metric of the respective erase unit in relation to the representative age metric of the plurality of erase units to generate an adjusted garbage collection control metric for the respective erase unit, and (4) performing garbage collection for the storage medium in accordance with the adjusted garbage collection control metrics of the plurality of erase units.

First claim

What is claimed is:

1. A method of wear leveling for a storage medium in a storage system, the method comprising:
determining, for each erase unit of a plurality of erase units in the storage medium, an age metric;
determining a representative age metric of the plurality of erase units;
for each respective erase unit of the plurality of erase units, biasing a respective garbage collection control metric for the respective erase unit in accordance with the age metric of the respective erase unit in relation to the representative age metric of the plurality of erase units to generate an adjusted garbage collection control metric for the respective erase unit, wherein biasing the respective garbage collection control metric includes:
calculating a difference between the age metric of the respective erase unit and the representative age metric of the plurality of erase units,
calculating a first value, the first value determined by multiplying the absolute value of the calculated difference by a predefined number of valid pages, and
biasing the respective garbage collection control metric by the calculated first value; and

performing garbage collection for the storage medium in accordance with the adjusted garbage collection control metrics of the plurality of erase units.

2. The method of claim 1 , wherein the garbage collection control metric is a valid-page count, and wherein biasing the respective valid-page count for the respective erase unit includes:
determining the respective valid-page count, wherein the respective valid-page count is a count of valid pages in the respective erase unit;
calculating a bias value for the respective erase unit in accordance with the age metric of the respective erase unit in relation to the representative age metric of the plurality of erase units;
in accordance with a first determination that the age metric of the respective erase unit corresponds to a shorter estimated remaining life than erase units having the representative age metric of the plurality of erase units, adding the bias value to the respective valid-page count for the respective erase unit to generate the adjusted valid-page count for the respective erase unit; and
in accordance with a second determination that the age metric of the respective erase unit corresponds to a longer estimated remaining life than erase units having the representative age metric of the plurality of erase units, subtracting the bias value from the respective valid-page count for the respective erase unit to generate the adjusted valid-page count for the respective erase unit.

3. The method of claim 1 , wherein:
the calculated first value is limited to a predefined maximum; and
the garbage collection control metric for the respective erase unit is biased by the limited first value.

4. The method of claim 2 , wherein performing garbage collection for the storage medium includes selecting an erase unit with a lowest adjusted valid-page count for garbage collection.

5. The method of claim 2 , wherein performing garbage collection for the storage medium includes performing garbage collection on a first erase unit with a first adjusted valid-page count prior to performing garbage collection on a second erase unit with a second adjusted valid-page count, wherein the first adjusted valid-page count is less than the second adjusted valid-page count.

6. The method of claim 1 , wherein biasing the respective garbage collection control metric for the respective erase unit includes:
determining the respective garbage collection control metric;
calculating a bias value for the respective erase unit in accordance with the age metric of the respective erase unit in relation to the representative age metric of the plurality of erase units, including limiting a range of the bias value to a predefined range; and
mathematically adjusting the respective garbage collection control metric for the respective erase unit with the calculated bias value to generate the adjusted garbage collection control metric for the respective erase unit.

7. The method of claim 1 , wherein the age metric for each erase unit is determined in accordance with a metric corresponding to estimated remaining life of each erase unit.

8. The method of claim 1 , wherein the erase unit is a single erase block.

9. The method of claim 1 , wherein the erase unit is a super block, wherein the super block includes a plurality of erase blocks.

10. The method of claim 1 , wherein the storage medium comprises one or more flash memory devices.

11. The method of claim 1 , wherein determining, for each erase unit of a plurality of erase units in the storage medium, the age metric comprises determining, for each storage unit of a plurality of storage units in the storage medium, an age metric for a respective storage unit, wherein each storage unit comprises a plurality of the erase units.

12. A device operable to perform wear leveling for a storage medium, the device comprising:
a storage medium interface for coupling the device to the storage medium; and
one or more modules, including a memory management module that includes one or more processors and memory storing one or more programs configured for execution by the one or more processors, the one or more modules coupled to the storage medium interface and configured to:
determine, for each erase unit of a plurality of erase units in the storage medium, an age metric;
determine a representative age metric of the plurality of erase units;
bias, for each respective erase unit of the plurality of erase units, a respective garbage collection control metric for the respective erase unit in accordance with the age metric of the respective erase unit in relation to the representative age metric of the plurality of erase units to generate an adjusted garbage collection control metric for the respective erase unit, wherein biasing the respective garbage collection control metric includes:
calculating a difference between the age metric of the respective erase unit and the representative age metric of the plurality of erase units,
calculating a first value, the first value determined by multiplying the absolute value of the calculated difference by a predefined number of valid pages, and
biasing the respective garbage collection control metric by the calculated first value; and
perform garbage collection for the storage medium in accordance with the adjusted garbage collection control metrics of the plurality of erase units.

13. The device of claim 12 , wherein the garbage collection control metric is a valid-page count, and wherein the one or more modules are configured to bias the respective valid-page count for the respective erase unit, including:
determining the respective valid-page count, wherein the respective valid-page count is a count of valid pages in the respective erase unit;
calculating a bias value for the respective erase unit in accordance with the age metric of the respective erase unit in relation to the representative age metric of the plurality of erase units;
in accordance with a first determination that the age metric of the respective erase unit corresponds to a shorter estimated remaining life than erase units having the representative age metric of the plurality of erase units, adding the bias value to the respective valid-page count for the respective erase unit to generate the adjusted valid-page count for the respective erase unit; and
in accordance with a second determination that the age metric of the respective erase unit corresponds to a longer estimated remaining life than erase units having the representative age metric of the plura

Assignees

• Sandisk Entpr Ip Llc

Inventors

• Fitzpatrick James
• Higgins James

Classifications

• G11C16/3495

  Circuits or methods to detect or delay wearout of nonvolatile EPROM or EEPROM memory devices, e.g. by counting numbers of erase or reprogram cycles, by using multiple memory areas serially or cyclically · CPC title

• G06F12/0246 Primary

  in block erasable memory, e.g. flash memory · CPC title

• G06F12/0253

  Garbage collection, i.e. reclamation of unreferenced memory · CPC title

• G06F2212/1036

  Life time enhancement · CPC title

• G06F2212/7211

  Wear leveling · CPC title