Variable bit encoding per NAND flash cell to improve device endurance and extend life of flash-based storage devices

Patent metadata

Field	Value
Publication number	US-9639282-B2
Application number	US-201514929166-A
Country	US
Kind code	B2
Filing date	Oct 30, 2015
Priority date	May 20, 2015
Publication date	May 2, 2017
Grant date	May 2, 2017

Abstract

Systems, methods, and/or devices are used to implement variable bit encoding to improve device endurance and extend life of storage devices. In some embodiments, the method includes detecting a trigger condition with respect to one or more non-volatile memory portions (e.g., portions configured to store data encoded in a first encoding format) of a plurality of non-volatile memory portions of a storage device. In accordance with detecting the trigger condition, the method includes: determining a current and an estimated endurance metric for the plurality of non-volatile memory portions (e.g., corresponding to estimated endurance after reconfiguration of the one or more portions to store data encoded in a second encoding format), and in accordance with a determination that reconfiguration criteria are satisfied (e.g., the estimated endurance metric comprises an improvement over the current endurance metric), reconfiguring the one or more portions to store data encoded in the second encoding format.

First claim

What is claimed is:

1. A method of operation in a storage device that comprises a storage controller and a plurality of non-volatile memory portions in one or more memory devices, the method comprising:
at the storage controller, the storage controller having one or more physical processors and memory:
detecting a trigger condition with respect to one or more non-volatile memory portions of the storage device, wherein the one or more non-volatile memory portions are configured to store data encoded in a first encoding format and having a first storage density corresponding to the first encoding format;
in accordance with detecting the trigger condition:
determining a current endurance metric for the plurality of non-volatile memory portions of the storage device;
determining an estimated endurance metric for the plurality of non-volatile memory portions of the storage device, the estimated endurance metric corresponding to an estimated endurance for the plurality of non-volatile memory portions of the storage device after a reconfiguration of the one or more non-volatile memory portions of the storage device to store data encoded in a second encoding format and having a second storage density; and
in accordance with a determination that reconfiguration criteria are satisfied, reconfiguring the one or more non-volatile memory portions of the storage device to store data encoded in the second encoding format and having the second storage density, the reconfiguration criteria including a determination that the estimated endurance metric comprises an improvement over the current endurance metric in accordance with predefined endurance improvement criteria.

2. The method of claim 1 , wherein the second storage density is a lower storage density than the first storage density.

3. The method of claim 1 , wherein the current endurance metric for the plurality of non-volatile memory portions corresponds to an average value of an endurance metric with respect to the plurality of non-volatile memory portions, and the estimated endurance metric for the plurality of non-volatile memory portions of the storage device corresponds to a projected average value of the endurance metric with respect to the plurality of non-volatile memory portions after the reconfiguring.

4. The method of claim 3 , wherein the endurance metric with respect to a single memory portion of the plurality of non-volatile memory portions is a value corresponding to a projected number of write operations that can be performed, prior to end of life, by the single memory portion, or a projected number of program/erase cycles that can be performed, prior to end of life, by the single memory portion.

5. The method of claim 1 , further comprising:
maintaining one or more status metrics for each memory portion of the plurality of non-volatile memory portions of the storage device, wherein a respective status metric for a respective memory portion corresponds to the respective memory portion's ability to retain data;
wherein detecting the trigger condition comprises:
in accordance with a determination that at least one of the one or more status metrics for the one or more non-volatile memory portions of the storage device satisfies a threshold, detecting the trigger condition as to the one or more non-volatile memory portions of the storage device.

6. The method of claim 1 , further comprising:
maintaining one or more status metrics for each of the one or more memory devices, wherein a first status metric of the one or more status metrics corresponds to a respective memory device's ability to retain data; and
in accordance with a determination that the one or more status metrics for a respective memory device of the one or more memory devices satisfy one or more end-of-life criteria, operating the respective memory device in read-only mode.

7. The method of claim 1 , wherein the one or more memory devices comprise one or more flash memory devices.

8. A storage device, comprising:
a set of one or more non-volatile memory devices, the set of one or more non-volatile memory devices including a plurality of non-volatile memory portions; and
a storage controller, the storage controller including one or more controller modules configured to:
detect a trigger condition with respect to one or more non-volatile memory portions of the storage device, wherein the one or more non-volatile memory portions are configured to store data encoded in a first encoding format and having a first storage density corresponding to the first encoding format; and
determine an estimated endurance metric for the plurality of non-volatile memory portions of the storage device, the estimated endurance metric corresponding to an estimated endurance for the plurality of non-volatile memory portions of the storage device after a reconfiguration of the one or more non-volatile memory portions of the storage device to store data encoded in a second encoding format and having a second storage density corresponding to the second encoding format; and
reconfigure, in accordance with a determination that reconfiguration criteria are satisfied, the one or more non-volatile memory portions of the storage device to store data encoded in the second encoding format and having the second storage density, the reconfiguration criteria including a determination that the estimated endurance metric comprises an improvement over the current endurance metric in accordance with predefined endurance improvement criteria.

9. The storage device of claim 8 , wherein the one or more controller modules include:
a trigger condition detection module to detect the trigger condition;
a metric maintaining module to determine the estimated endurance metric; and
a reconfiguration module to reconfigure the one or more non-volatile memory portions of the storage device in response to the trigger condition and in accordance with the determination that the reconfiguration criteria are satisfied.

10. The storage device of claim 8 , wherein the second storage density is a lower storage density than the first storage density.

11. The storage device of claim 8 , wherein the current endurance metric for the plurality of non-volatile memory portions corresponds to an average value of an endurance metric with respect to the plurality of non-volatile memory portions, and the estimated endurance metric for the plurality of non-volatile memory portions of the storage device corresponds to a projected average value of the endurance metric with respect to the plurality of non-volatile memory portions after the reconfiguring.

12. The storage device of claim 11 , wherein the endurance metric with respect to a single memory portion of the plurality of non-volatile memory portions is a value corresponding to a projected number of write operations that can be performed, prior to end of life, by the single memory portion, or a projected number of program/erase cycles that can be performed, prior to end of life, by the single memory portion.

13. The storage device of claim 8 , wherein the one or more controller modules are further configured to:
maintain one or more status metrics for each memory portion of the plurality of non-volatile memory portions of the storage device, wherein a respective status metric for a respective memory portion corresponds to the respective memory portion's ability to retain data;
wherein detecting the trigger condition comprises:
in accordance with a determination that at least one of the one or more status metrics for the one or more non-volatile memory portions of the storage device satisfies a threshold, detecting the trigger condition as to the

Assignees

• Sandisk Entpr Ip Llc
• Sandisk Technologies Llc

Inventors

• Kankani Navneeth
• Truong Linh Tien

Classifications

• G06F2212/7204

  Capacity control, e.g. partitioning, end-of-life degradation · CPC title

• G06F2212/1036

  Life time enhancement · CPC title

• G06F12/0246 Primary

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

• G06F2212/1044

  Space efficiency improvement · CPC title

• G06F3/0653

  Monitoring storage devices or systems · CPC title