Securely erasing flash-based memory

• US 8,130,554 B1
• Filed: 09/29/2008
• Issued: 03/06/2012
• Est. Priority Date: 09/29/2008
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Linnell, Thomas E.
• Primary Examiner(s): Ho, Hoai V
• Application Number:
  US12/240,100
• Time in Patent Office: 1,254 Days
• Field of Search: 365/185.28, 365/185.29, 711/159
• US Class Current: 365/185.28
• CPC Class Codes: G11C 16/14 Circuits for erasing electrically, e.g. erase voltage switching circuits
• CPC Class Codes: G11C 16/22 Safety or protection circuits preventing unauthorised or accidental access to memory cells

Abstract

A method is used in securely erasing flash-based memory. A new version of data is received for a logical location of a flash-based memory. An old version of the data of the logical location is stored in a first physical location in the flash-based memory. The old version of the data is caused to be subject to an obscure operation. The new version of the data is caused to be stored in a second physical location in the flash-based memory.

Claims

1. A method for use in securely erasing flash-based memory, the method comprising:

receiving a new version of data for a logical location of a flash-based memory, an old version of the data of the logical location being stored in a first physical location in the flash-based memory;

causing the old version of the data to be subject to an obscure operation; and

causing the new version of the data to be stored in a second physical location in the flash-based memory.

2. The method of claim 1, further comprising:

applying garbage collection to the first physical location.

3. The method of claim 1, wherein the first physical location comprises NAND flash based memory.

4. The method of claim 1, wherein the contents of the first physical location continues to persist in a technologically accessible state until a block containing the first physical location is erased.

5. The method of claim 1, further comprising:

applying partial programming to the first physical location.

6. The method of claim 1, further comprising:

programming an unprogrammed bit at the first physical location.

7. The method of claim 1, further comprising:

reprogramming the first physical location to an all “

0”

s state.

8. The method of claim 1, further comprising:

setting an invalid state for the first physical location.

9. The method of claim 1, further comprising:

forcing an obscure operation on old data for every write to the flash-based memory.

10. The method of claim 1, further comprising:

for an overwrite operation, writing “

0”

s to the logical location.

11. The method of claim 1, wherein bits in the flash-based memory can only change state in one direction.

12. The method of claim 1, further comprising:

subjecting error correcting code redundancy data to the obscure operation.

13. The method of claim 1, wherein the obscure operation is performed at page-level granularity.

14. The method of claim 1, further comprising:

causing all write updates to the logical location to obscure the old version of the data.

15. A system for use in securely erasing flash-based memory, the system comprising:

first logic receiving a new version of data for a logical location of a flash-based memory, an old version of the data of the logical location being stored in a first physical location in the flash-based memory;

second logic causing the old version of the data to be subject to an obscure operation; and

third logic causing the new version of the data to be stored in a second physical location in the flash-based memory.

16. The system of claim 15, further comprising:

fourth logic applying garbage collection to the first physical location.

17. The system of claim 15, wherein the first physical location comprises NAND flash based memory.

18. The system of claim 15, wherein the contents of the first physical location continues to persist in a technologically accessible state until a block containing the first physical location is erased.

19. The system of claim 15, further comprising:

fifth logic applying partial programming to the first physical location.