Method and system for recharacterizing the storage density of a memory device or a portion thereof

• US 9,645,749 B2
• Filed: 07/01/2014
• Issued: 05/09/2017
• Est. Priority Date: 05/30/2014
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Inventors: Truong, Linh Tien, Samuels, Allen, Kankani, Navneeth
• Primary Examiner(s): GIARDINO JR, MARK A
• Application Number:
  US14/321,701
• Publication Number:
  US 20150347039A1
• Time in Patent Office: 1,043 Days
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/0634 by changing the state or mode of one or more devices
• CPC Class Codes: G06F 3/0653 Monitoring storage devices or systems
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G11C 11/5621 using charge storage in a floating gate
• CPC Class Codes: G11C 13/0035 Evaluating degradation, retention or wearout, e.g. by counting writing cycles
• CPC Class Codes: G11C 16/3495 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 Class Codes: G11C 2211/5641 Multilevel memory having cells with different number of storage levels

Abstract

A storage system includes a memory controller and a storage device with one or more memory devices, each with a plurality of memory portions. The memory controller determines an initial storage capacity for each of the one or more memory devices, where the one or more memory devices are configured in a first storage density. The memory controller detects a trigger condition as to at least one memory portion of a respective device of the one or more memory devices and, in response to detecting the trigger condition, recharacterizes the at least one memory portion of the respective memory device so as to be configured in a second storage density, where the at least one recharacterized memory portion of the respective memory device has a reduced storage capacity. After the recharacterizing, the memory controller determines a revised storage capacity for the respective memory device.

Claims

1. A method of operation in a storage system that comprises a memory controller and one or more memory devices, each with a plurality of memory portions, the method comprising:

at the memory controller;

maintaining one or more status metrics for each memory portion of the plurality of memory portions of the one or more memory devices, wherein each of the one or more status metrics for a respective memory portion corresponds to the respective memory portion'"'"'s ability to retain data;

determining an initial storage capacity for each of the one or more memory devices, wherein the one or more memory devices are configured in a first storage density;

in accordance with a determination that at least one of the one or more status metrics for at least one memory portion of a respective memory device of the one or more memory devices satisfies one or more predefined criteria, detecting a trigger condition as to the at least one memory portion of the respective memory device, wherein detecting the trigger condition as to the at least one memory portion of the respective memory device includes receiving a command from a host system to recharacterize the at least one memory portion of the respective memory device;

in response to detecting the trigger condition, recharacterizing the at least one memory portion of the respective memory device so as to be configured in a second storage density, wherein the at least one recharacterized memory portion of the respective memory device has a reduced storage capacity;

after the recharacterizing, determining a revised storage capacity for the respective memory device;

after determining the initial storage capacities of the one or more memory devices, reporting, to the host system, the initial storage capacity of at least one of the one or more memory devices; and

after determining the revised storage capacity for the respective memory device, reporting, to the host system, the revised storage capacity of the respective memory device.

2. The method of claim 1, further comprising:

in response to detecting the trigger condition and prior to the recharacterizing, migrating data stored in the at least one memory portion of the respective memory device to another memory portion in the storage system.

3. The method of claim 1, further comprising:

receiving a query; and

in response to receiving the query, reporting at least one of the one or more status metrics for at least one of the one or more memory devices.

4. The method of claim 1, further comprising:

receiving a memory command to write write data to the storage system;

in response to receiving the memory command, writing the write data to the one or more memory devices; and

after writing the write data, sending a notification acknowledging writing the write data, wherein the notification also includes at least one of the one or more status metrics for at least one of the one or more memory devices.

5. The method of claim 1, wherein maintaining the one or more status metrics for each memory portion includes determining, in conjunction with the recharacterizing of the at least one memory portion of the respective memory device, an increased value for at least one of the one or more status metrics for the at least one memory portion of the respective memory device, wherein the increased value for the at least one memory portion corresponds to an increased amount of wear remaining with respect to the at least one memory portion.

6. The method of claim 1, wherein the initial storage capacity reported to the host system is initial storage capacity excluding over provisioning and wherein the revised storage capacity reported to the host system is revised storage capacity excluding over provisioning.

7. The method of claim 1, wherein, while the one or more memory devices are configured in the first storage density, memory cells comprising the one or more memory devices have a storage capacity of N bits of data, wherein N is greater than zero, and

wherein, after the at least one memory portion is recharacterized so as to be configured in the second storage density, the memory cells comprising the at least one memory portion each have a storage capacity of M bits of data, wherein M is greater than zero and M is less than N.

8. The method of claim 1, wherein the one or more memory devices are flash memory devices, and

wherein each portion of the plurality of memory portions of the respective memory device comprises one of the set of:

one die, one erase block, and one page.

9. The method of claim 1, wherein the one or more memory devices comprises one or more three-dimensional (3D) memory devices, each with a 3D array of memory cells, and circuitry associated with operation of memory elements in the one or more 3D memory devices.

10. The method of claim 9, wherein the circuitry and one or more memory elements in a respective 3D memory device, of the one or more 3D memory devices, are on the same substrate.

11. A storage system, comprising:

a storage device including one or more memory devices, each with a plurality of memory portions; and

a memory controller with one or more processors and memory storing one or more programs to be executed by the one or more processors, the one or more programs comprising instructions for;

maintaining one or more status metrics for each memory portion of the plurality of memory portions of the one or more memory devices, wherein each of the one or more status metrics for a respective memory portion corresponds to the respective memory portion'"'"'s ability to retain data;

determining an initial storage capacity for each of the one or more memory devices, wherein the one or more memory devices are configured in a first storage density;

in accordance with a determination that at least one of the one or more status metrics for at least one memory portion of a respective memory device of the one or more memory devices satisfies one or more predefined criteria, detecting a trigger condition as to the at least one memory portion of the respective memory device, wherein detecting the trigger condition as to the at least one memory portion of the respective memory device includes receiving a command from a host system to recharacterize the at least one memory portion of the respective memory device;

in response to detecting the trigger condition, recharacterizing the at least one memory portion of the respective memory device so as to be configured in a second storage density, wherein the at least one recharacterized memory portion of the respective memory device has a reduced storage capacity;

after the recharacterizing, determining a revised storage capacity for the respective memory device;

after determining the initial storage capacities of the one or more memory devices, reporting, to the host system, the initial storage capacity of at least one of the one or more memory devices; and

after determining the revised storage capacity for the respective memory device, reporting, to the host system, the revised storage capacity of the respective memory device.

12. The storage system of claim 11, wherein maintaining the one or more status metrics for each memory portion includes determining, in conjunction with the recharacterizing of the at least one memory portion of the respective memory device, an increased value for at least one of the one or more status metrics for the at least one memory portion of the respective memory device, wherein the increased value for the at least one memory portion corresponds to an increased amount of wear remaining with respect to the at least one memory portion.

13. The storage system of claim 11, wherein the initial storage capacity reported to the host system is initial storage capacity excluding over provisioning and wherein the revised storage capacity reported to the host system is revised storage capacity excluding over provisioning.

14. The storage system of claim 11, wherein the one or more programs further comprise instructions for:

in response to detecting the trigger condition and prior to the recharacterizing, migrating data stored in the at least one memory portion of the respective memory device to another memory portion in the storage system.

15. A non-transitory computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which, when executed by a memory controller with one or more processors, cause the memory controller to perform operations comprising:

maintaining one or more status metrics for each memory portion of a plurality of memory portions of one or more memory devices, wherein each of the one or more status metrics for a respective memory portion corresponds to the respective memory portion'"'"'s ability to retain data;

determining an initial storage capacity for each of the one or more memory devices, wherein the one or more memory devices are configured in a first storage density and the one or more memory devices each include a plurality of memory portions;

in accordance with a determination that at least one of the one or more status metrics for at least one memory portion of a respective memory device of the one or more memory devices satisfies one or more predefined criteria, detecting a trigger condition as to the at least one memory portion of the respective memory device, wherein detecting the trigger condition as to the at least one memory portion of the respective memory device includes receiving a command from a host system to recharacterize the at least one memory portion of the respective memory device;

in response to detecting the trigger condition, recharacterizing the at least one memory portion of the respective memory device so as to be configured in a second storage density, wherein the at least one recharacterized memory portion of the respective memory device has a reduced storage capacity;

after the recharacterizing, determining a revised storage capacity for the respective memory device;

after determining the initial storage capacities of the one or more memory devices, reporting, to the host system, the initial storage capacity of at least one of the one or more memory devices; and

after determining the revised storage capacity for the respective memory device, reporting, to the host system, the revised storage capacity of the respective memory device.

16. The non-transitory computer readable storage medium of claim 15, wherein maintaining the one or more status metrics for each memory portion includes determining, in conjunction with the recharacterizing of the at least one memory portion of the respective memory device, an increased value for at least one of the one or more status metrics for the at least one memory portion of the respective memory device, wherein the increased value for the at least one memory portion corresponds to an increased amount of wear remaining with respect to the at least one memory portion.

17. The non-transitory computer readable storage medium of claim 15, wherein the initial storage capacity reported to the host system is initial storage capacity excluding over provisioning and wherein the revised storage capacity reported to the host system is revised storage capacity excluding over provisioning.

18. The non-transitory computer readable storage medium of claim 15, wherein the one or more programs further comprise instructions for:

in response to detecting the trigger condition and prior to the recharacterizing, migrating data stored in the at least one memory portion of the respective memory device to another memory portion in the storage system.