Determination of data integrity based on sentinel cells

Abstract

An apparatus can have an array of memory cells and a controller coupled to the array. The controller can be configured to read a group sentinel cells of the array and without reading a number of other groups of cells of the array to determine that data stored in the number of other groups of cells lacks integrity based on a determination that data stored in the group of sentinel cells lacks integrity.

1 .- 20 . (canceled) 
     
     
         21 . An apparatus, comprising:
 an array of memory cells; and   a controller coupled to the array, wherein the controller is configured to:
 read a group of sentinel cells of the array, wherein the group of sentinel cells has a corresponding write stamp indicating when data was last written to the group of sentinel cells; and 
 responsive to determining that the data stored in the group of sentinel cells lacks integrity, refreshing only those groups of cells of a plurality of other groups of cells whose corresponding write stamps indicate data was written to the groups of cells prior to when the data was last written to the sentinel cells. 
   
     
     
         22 . The apparatus of  claim 21 , wherein the controller is configured to determine that the data stored in the group of sentinel cells lacks integrity in response to determining that the data stored in the group of sentinel cells comprises greater than a threshold quantity of errors. 
     
     
         23 . The apparatus of  claim 21 , wherein the controller is configured to determine those groups of cells of the plurality of other groups of cells whose corresponding write stamps indicate data was written to the groups of cells prior to when the data was last written to the sentinel cells by comparing the write stamp corresponding to the group of sentinel cells to the respective write stamps corresponding to the plurality of other groups of cells. 
     
     
         24 . The apparatus of  claim 23 , wherein the write stamp corresponding to the group of sentinel cells indicates a quantity of writes to the array at a time when the data stored in the group of sentinel cells is written to the array. 
     
     
         25 . The apparatus of  claim 21 , wherein the controller is configured to write data to the group of sentinel cells once for every N times that data is written to the plurality of other groups of cells. 
     
     
         26 . The apparatus of  claim 21 , wherein the group of sentinel cells is located in a particular physical block of the array, and wherein the plurality of other groups of cells are located in respective different physical blocks of the array. 
     
     
         27 . The apparatus of  claim 21 , wherein the controller is configured to periodically change which group of cells is used as the group of sentinel cells. 
     
     
         28 . The apparatus of  claim 21 , wherein the controller is configured to maintain a counter of writes to physical blocks of the array, and wherein the write stamp corresponding to the group of sentinel cells is based on a value of the counter at the time data is written to the group of sentinel cells. 
     
     
         29 . The apparatus of  claim 28 , wherein the controller is configured to periodically read the group of sentinel cells at a frequency based on the write stamp corresponding to the group of sentinel cells. 
     
     
         30 . An apparatus, comprising:
 an array of memory cells comprising a group of sentinel cells and a plurality of groups of non-sentinel cells; and   a controller coupled to the array of memory cells, wherein the controller is configured to:
 increment a write count corresponding to the array each time a write operation is performed on the array; 
 perform a read on the group of sentinel memory cells, wherein the group of sentinel memory cells stores sentinel data and has a first write stamp corresponding thereto, wherein the first write stamp is based on the write count at a time the group of sentinel memory cells was last written; 
 determine a quality of the sentinel data based on the read; 
 responsive to a determination that the sentinel data lacks quality:
 determine those groups of the plurality of groups of non-sentinel cells whose corresponding second write stamp indicates that they were written prior to the time the group of sentinel memory cells was last written; and 
 perform a refresh operation on only those groups of the plurality of groups of non-sentinel memory cells determined to be written prior to the time the group of sentinel cells was last written. 
 
   
     
     
         31 . The apparatus of  claim 30 , wherein the controller is configured to write data to the group of sentinel memory cells after each N increments of the write count. 
     
     
         32 . The apparatus of  claim 30 , wherein the second write stamps corresponding to the respective plurality of groups of non-sentinel memory cells are stored as metadata along with user data in the respective plurality of groups of non-sentinel memory cells. 
     
     
         33 . The apparatus of  claim 32 , wherein the first write stamp corresponding to the group of sentinel memory cells is stored as metadata along with user data in the group of sentinel memory cells. 
     
     
         34 . The apparatus of  claim 30 , wherein the controller is configured to maintain a table indicating to which of the plurality of groups of non-sentinel memory cells the respective second write stamps correspond. 
     
     
         35 . The apparatus of  claim 30 , wherein the controller is configured to determine those groups of the plurality of groups of non-sentinel cells whose corresponding second write stamp indicates that they were written prior to the time the group of sentinel memory cells was last written by reading metadata stored in the respective groups of non-sentinel memory cells and without reading user data stored in the respective groups of non-sentinel memory cells. 
     
     
         36 . A method, comprising:
 incrementing a write count corresponding to an array of memory cells each time a write operation is performed on the array, wherein the array comprises a number of groups of sentinel cells and a plurality of groups of non-sentinel cells;   performing a read on a particular group of the number of groups of sentinel memory cells, wherein the number of groups of sentinel memory cells store sentinel data and have respective first write stamps corresponding thereto, wherein the first write stamps are based on the write count at a time the respective groups of sentinel memory cells were last written;
 determine a quality of the sentinel data stored in the particular group based on the read; 
 responsive to a determination that the sentinel data stored in the particular group lacks quality:
 determine those groups of the plurality of groups of non-sentinel cells whose corresponding second write stamp indicates that they were written prior to the time the particular group of sentinel memory cells was last written; and 
 perform a refresh operation on only those groups of the plurality of groups of non-sentinel memory cells determined to be written prior to the time the particular group of sentinel cells was last written. 
 
   
     
     
         37 . The method of  claim 36 , further comprising performing periodic reads on the number of groups of sentinel memory cells to determine the quality of the sentinel data stored in the respective groups of sentinel memory cells, wherein the periodic reads are done based on the write count. 
     
     
         38 . The method of  claim 36 , wherein the method includes performing the periodic reads on the number of groups of sentinel memory cells after each N increments of the write count. 
     
     
         39 . The method of  claim 36 , further comprising updating the data and corresponding first write stamps of the number of groups of sentinel memory cells via writes to the number of groups of sentinel memory cells, wherein a different one of the number of groups of sentinel memory cells is written after each N increments of the write count. 
     
     
         40 . The method of  claim 36 , further comprising storing the respective first write stamps corresponding to the number groups of sentinel memory cells and the respective second write stamps corresponding to the plurality of groups of non-sentinel memory cells in metadata stored along with corresponding user data.