Erase health metric to rank memory portions

• US 10,732,856 B2
• Filed: 10/04/2016
• Issued: 08/04/2020
• Est. Priority Date: 03/03/2016
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Inventors: Yang, Nian Niles, Bauche, Alexandra
• Primary Examiner(s): Farrokh, Hashem
• Application Number:
  US15/285,407
• Publication Number:
  US 20170255399A1
• Time in Patent Office: 1,400 Days
• Field of Search: 711103
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0688 Non-volatile semiconductor memory arrays

Abstract

An exemplary method to rank blocks of a non-volatile memory device includes: for each of a plurality of blocks of a memory device, determining a respective erase health metric (EHM) for each of the blocks by combining an erase difficulty metric and an age metric, including: calculating the erase difficulty metric for a respective block based on erase performance metrics obtained during erase phases of an erase operation performed on the respective block, and determining the age metric for the respective block based on a total number of erase operations performed on the respective block during its lifespan. After determining the respective EHM for each of the blocks, the method includes ranking blocks in accordance with the determined respective EHMs, and selecting a block of the plurality of blocks in accordance with the rankings, and writing data to the selected block.

Claims

1. A method, comprising:

for each of a plurality of non-volatile memory portions of a non-volatile memory device, determining a respective erase health metric for each of the plurality of non-volatile memory portions by combining an erase difficulty metric and an age metric, including;

calculating the erase difficulty metric for a respective non-volatile memory portion, wherein the erase difficulty metric for the respective non-volatile memory portion is based on one or more erase performance metrics obtained during a plurality of erase phases of an erase operation performed on the respective non-volatile memory portion;

wherein;

each of the plurality of erase phases of the erase operation performed on the respective non-volatile memory portion comprises;

performing an erase using an erase voltage; and

determining an erase statistic for the performed erase, wherein the erase statistic for the performed phase includes a number of non-erased memory cells in the respective non-volatile memory portion having cell voltages that fail to satisfy a criterion corresponding to the performed erase; and

the one or more erase performance metrics include;

the number of non-erased memory cells in the respective non-volatile memory portion; and

a change in voltage between an initial erase voltage used during an initial erase phase of the erase operation on the respective non-volatile memory portion, and a final erase voltage used in a final erase phase of the erase operation on the respective non-volatile memory portion; and

determining the age metric for the respective non-volatile memory portion based on a total number of erase operations performed on the respective non-volatile memory portion during a lifespan of the non-volatile memory device; and

after determining the respective erase health metric for each of the plurality of non-volatile memory portions of the non-volatile memory device;

ranking non-volatile memory portions, including at least the plurality of non-volatile memory portions of the non-volatile memory device, in accordance with the determined respective erase health metrics; and

selecting a non-volatile memory portion of the plurality of non-volatile memory portions in accordance with the ranking of the non-volatile memory portions, and writing data to the selected non-volatile memory portion.

2. The method of claim 1, wherein:

said ranking includes determining a highest ranked non-volatile memory portion of the non-volatile memory device; and

writing data to the selected non-volatile memory portion comprises writing data to the highest ranked non-volatile memory portion.

3. The method of claim 1, wherein the one or more erase performance metrics further include:

a number of successive erase phases required to satisfy a stopping condition during the erase operation on the respective non-volatile memory portion.

4. The method of claim 3, wherein calculating the erase difficulty metric includes calculating the erase difficulty metric in accordance with:

a first normalization coefficient associated with the number of successive erase phases of the erase operation performed on the respective non-volatile memory portion; and

a second normalization coefficient associated with the total number of erase operations performed on the respective non-volatile memory portion during the lifespan of the non-volatile memory device, wherein the first normalization coefficient is inversely related to the second normalization coefficient.

5. The method of claim 3, wherein calculating the erase difficulty metric for the respective non-volatile memory portion includes calculating a weighted sum of two or more of the erase performance metrics for the respective non-volatile memory portion.

6. The method of claim 3, wherein:

the one or more erase performance metrics further include a weighted sum of counts; and

each count in the weighted sum of counts comprises an erase statistic for the respective non-volatile memory portion after each of two or more of the successive erase phases.

7. The method of claim 1, further comprising:

after ranking said non-volatile memory portions, generating an ordered list of non-volatile memory portions of the non-volatile memory device based on their respective erase difficulty metrics.

8. The method of claim 1, wherein:

said ranking of the non-volatile memory portions includes ranking two or more non-volatile memory portions having a same erase health metric in accordance with a tie-breaker metric; and

the tie-breaker metric for each non-volatile memory portion of the two or more non-volatile memory portions is based at least in part on the total number of erase operations performed on the non-volatile memory portion during the lifespan of the non-volatile memory device.

9. The method of claim 1, wherein:

the data includes one or more data streams; and

writing the data to the selected non-volatile memory portion comprises writing a first data stream of the one or more data streams to the selected non-volatile memory portion of the non-volatile memory device.

10. A storage system, comprising:

a storage medium;

one or more processors; and

memory storing one or more programs, which when executed by the one or more processors cause the storage system to;

for each of a plurality of non-volatile memory portions of a non-volatile memory device, determine a respective erase health metric for each of the plurality of non-volatile memory portions by combining an erase difficulty metric and an age metric, including;

calculate the erase difficulty metric for a respective non-volatile memory portion, wherein the erase difficulty metric for the respective non-volatile memory portion is based on one or more erase performance metrics obtained during a plurality of erase phases of an erase operation performed on the respective non-volatile memory portion;

wherein;

each of the plurality of erase phases of the erase operation performed on the respective non-volatile memory portion comprises;

performing an erase using an erase voltage; and

determining an erase statistic for the performed erase, wherein the erase statistic for the performed phase includes a number of non-erased memory cells in the respective non-volatile memory portion having cell voltages that fail to satisfy a criterion corresponding to the performed erase; and

the one or more erase performance metrics include;

the number of non-erased memory cells in the respective non-volatile memory portion; and

a change in voltage between an initial erase voltage used during an initial erase phase of the erase operation on the respective non-volatile memory portion, and a final erase voltage used in a final erase phase of the erase operation on the respective non-volatile memory portion; and

determine the age metric for the respective non-volatile memory portion based on a total number of erase operations performed on the respective non-volatile memory portion during a lifespan of the non-volatile memory device; and

after determining the respective erase health metric for each of the plurality of non-volatile memory portions of the non-volatile memory device;

rank non-volatile memory portions, including at least the plurality of non-volatile memory portions of the non-volatile memory device, in accordance with the determined respective erase health metrics; and

select a non-volatile memory portion of the plurality of non-volatile memory portions in accordance with the ranking of the non-volatile memory portions, and write data to the selected non-volatile memory portion.

11. The storage system of claim 10, wherein the one or more programs include:

an erase module having instructions for determining the erase health metric; and

a block ranking module having instructions for ranking the non-volatile memory portions in accordance with the determined respective erase health metrics.

12. The storage system of claim 10, wherein said ranking includes:

determining a highest ranked non-volatile memory portion of the non-volatile memory device; and

writing data to the selected non-volatile memory portion comprises writing data to the highest ranked non-volatile memory portion.

13. The storage system of claim 10, wherein the one or more erase performance metrics further include:

a number of successive erase phases required to satisfy a stopping condition during the erase operation on the respective non-volatile memory portion.

14. The storage system of claim 13, wherein calculating the erase difficulty metric includes calculating the erase difficulty metric in accordance with:

a first normalization coefficient associated with the number of successive erase phases of the erase operation performed on the respective non-volatile memory portion; and

a second normalization coefficient associated with the total number of erase operations performed on the respective non-volatile memory portion during the lifespan of the non-volatile memory device, wherein the first normalization coefficient is inversely related to the second normalization coefficient.

15. The storage system of claim 13, wherein calculating the erase difficulty metric for the respective non-volatile memory portion includes calculating a weighted sum of two or more of the erase performance metrics for the respective non-volatile memory portion.

16. The storage system of claim 13, wherein:

the one or more erase performance metrics further include a weighted sum of counts; and

each count in the weighted sum of counts comprises an erase statistic for the respective non-volatile memory portion after each of two or more of the successive erase phases.

17. The storage system of claim 10, wherein the one or more programs further include instructions, which when executed by the one or more processors cause the storage system to, after ranking said non-volatile memory portions, generate an ordered list of non-volatile memory portions of the non-volatile memory device based on their respective erase difficulty metrics.

18. A storage system, comprising:

means for determining, for each of a plurality of non-volatile memory portions of a non-volatile memory device, a respective erase health metric for each of the plurality of non-volatile memory portions by combining an erase difficulty metric and an age metric, including;

means for calculating the erase difficulty metric for a respective non-volatile memory portion, wherein the erase difficulty metric for the respective non-volatile memory portion is based on one or more erase performance metrics obtained during a plurality of erase phases of an erase operation performed on the respective non-volatile memory portion;

wherein;

each of the plurality of erase phases of the erase operation performed on the respective non-volatile memory portion comprises;

performing an erase using an erase voltage; and

determining an erase statistic for the performed erase, wherein the erase statistic for the performed phase includes a number of non-erased memory cells in the respective non-volatile memory portion having cell voltages that fail to satisfy a criterion corresponding to the performed erase; and

the one or more erase performance metrics include;

the number of non-erased memory cells in the respective non-volatile memory portion; and

a change in voltage between an initial erase voltage used during an initial erase phase of the erase operation on the respective non-volatile memory portion, and a final erase voltage used in a final erase phase of the erase operation on the respective non-volatile memory portion; and

means for determining the age metric for the respective non-volatile memory portion based on a total number of erase operations performed on the respective non-volatile memory portion during a lifespan of the non-volatile memory device; and

means for ranking non-volatile memory portions, including at least the plurality of non-volatile memory portions of the non-volatile memory device, in accordance with the determined respective erase health metrics; and

means for selecting a non-volatile memory portion of the plurality of non-volatile memory portions in accordance with the ranking of the non-volatile memory portions, and write data to the selected non-volatile memory portion.