Storage system and method for boundary wordline data retention handling
A storage system and method for boundary wordline data retention handling are provided. In one embodiment, the storage system includes a memory having a single-level cell (SLC) block and a multi-level cell (MLC) block. The system determines if the boundary wordline in the MLC block has a data retention problem (e.g., by determining how long it has been since the boundary wordline was programmed). To address the data retention problem, the storage system can copy data from a wordline in the SLC block that corresponds to the boundary wordline in the MLC block to a wordline in another SLC block prior to de-committing the data in the SLC block. Alternatively, the storage system can reprogram the data in the boundary wordline using a double fine programing technique.
1. A storage system, comprising:
a memory comprising a first single-level cell (SLC) memory area, a second SLC memory area, and a multi-level cell (MLC) memory area; and
a controller configured to communicate with the memory and further configured to:
write data to both the first SLC memory area and the MLC memory area;
determine whether the controller is ready to de-commit the data from the first SLC memory area in response to a threshold number of wordlines in the MLC memory area finishing a multi-stage programming operation; and
in response to determining that the controller is ready to de-commit the data from the first SLC memory area:
determine whether an amount of time that has passed since a last-written wordline in the MLC memory area was written is longer than a threshold amount of time; and
in response to determining that the amount of time is longer than the threshold amount of time:
copy data from a wordline in the first SLC memory area that corresponds to the last-written wordline in the MLC memory area to a wordline in the second SLC memory area; and
update a mapping table to reflect the copy.
2. The storage system of claim 1 , wherein the controller is further configured to, in response to a command to read the MLC memory area:
read data from wordlines written prior to the last-written wordline in the MLC memory area; and
instead of reading the last-written wordline in the MLC memory area, read the data from the wordline in the second SLC memory area.
3. The storage system of claim 1 , wherein the controller is further configured to log an identification of the last-written wordline in the MLC memory area and a time when the last-written wordline was written.
4. The storage system of claim 3 , wherein the identification and time are logged in volatile memory in the storage system.
5. The storage system of claim 1 , wherein the controller is further configured to de-commit the data from the first SLC memory area.
6. The storage system of claim 1 , wherein the MLC memory area comprises a quad-level cell (QLC) memory area.
7. The storage system of claim 1 , wherein the memory comprises a three-dimensional memory.
8. The storage system of claim 1 , wherein the storage system is configured to be integrated in a host.
9. The storage system of claim 1 , wherein the storage system is configured to be removably connected with a host.
10. The storage system of claim 1 , wherein the controller is ready to de-commit the data after completing a rolling fold operation.
11. In a storage system including a memory comprising a single-level cell (SLC) block and a multi-level cell (MLC) block, a method comprising:
programming data to both the SLC block and the MLC block;
determining whether the storage system is ready to de-commit the data from the SLC block in response to a threshold number of wordlines in the MLC block finishing a multi-stage programming operation; and
in response to determining that the storage system is ready to de-commit the data from the SLC block:
determining whether a predetermined amount of time has passed since a boundary wordline in the MLC block was programmed; and
in response to determining that the predetermined amount of time has passed, re-programming the data in the boundary wordline in the MLC block.
12. The method of claim 11 , wherein the data is programmed in the boundary wordline in the MLC block using a fine programing technique, and wherein the data is re-programmed in the boundary wordline using a double fine programing technique.
13. The method of claim 11 , further comprising logging an identification of the boundary wordline in the MLC block and a time when the boundary wordline was written.
14. The method of claim 13 , wherein the identification and time are logged in volatile memory in the storage system.
15. The method of claim 11 , further comprising de-committing the data from the SLC block.
16. The method of claim 11 , wherein the MLC block comprises a quad-level cell (QLC) block.
17. The method of claim 11 , wherein the storage system is ready to de-commit the data after a rolling fold operation.
18. A storage system, comprising:
a memory comprising a first single-level cell (SLC) memory area, a second SLC memory area, and a multi-level cell (MLC) memory area;
means for writing data to both the first SLC memory area and the MLC memory area;
means for determining whether the storage system is ready to de-commit the data from the first SLC memory area in response to a threshold number of wordlines in the MLC memory area finishing a multi-stage programming operation; and
means for, in response to determining that the storage system is ready to de-commit the data from the first SLC memory area:
determining whether an amount of time that has passed since a last-written wordline in the MLC memory area was written is longer than a threshold amount of time; and
in response to determining that the amount of time is longer than the threshold amount of time:
copying data from a wordline in the first SLC memory area that corresponds to the last-written wordline in the MLC memory area to a wordline in the second SLC memory area; and
updating a mapping table to reflect the copy.
19. The storage system of claim 18 , further comprising means for re-programming the data in the last-written wordline in the MLC memory area.
20. The storage system of claim 19 , wherein the data is programmed in the last-written wordline in the MLC memory area using a fine programing technique, and wherein the data is re-programmed in the last-written wordline using a double fine programing technique.
21. The storage system of claim 18 , further comprising means for logging an identification of the last-written wordline in the MLC memory area and a time when the last-written wordline was written.
22. The storage system of claim 18 , wherein the storage system is ready to de commit the data from the SLC memory area after a rolling fold operation.