Patent Application
20130124778
The present invention relates to a method for storing host data and meta data in the same page of a non-volatile memory, in which the page of data is the minimum amount of data that can be read from or written to the non-volatile memory in a single operation. The present invention also relates to a memory controller that executes the foregoing described method as well as a memory system with a memory controller that executes the method.
Non-volatile memory chips that store or read a unit of data at a time, such as a page of data, are well known in the art. For example, NAND memory chips typically can store a page, such as 4 kilobytes, of data in the chip at each write operation. (Typically, a plurality of such pages are erased together in a unit called a block). Other types of non-volatile memory devices that store or read a page of data at a time, include so called managed NAND memory devices, such as the NANDrive memory device available from Greenliant Systems, Inc. of Santa Clara Calif..
In a NAND memory chip, the memory can be written to or read from only in units of data at a time, called pages. Because of their ability to read back a page of data at a time, NAND memory chips are useful to store large amounts of data.
In the prior art, because NAND memory chips are subject to error, the memory controller associated with the NAND memory chip generates error checking data, such as ECC bits. Error checking bits are of course dependent upon the underlying data (“host data”). In addition, the memory controller may also generate data referencing or correlating the location of the page of data in the NAND memory chip where the host data is stored or to be stored with the logical address. All of these types of data, such as ECC data, or data correlating physical address to logical address are referred to as meta data. The meta data is generated by the memory controller, based upon the host data or the location of the host data.
In the prior art, the manufacturers of the NAND memory chip have designed their memory chips such that a page also has spare bytes associated with that page. The number of spare bytes associated with each page of bits has varied from manufacturer to manufacturer. These spare bytes, however, are not user accessible to store host data and may be used only by the associated memory controller to store data such as error correction data associated with the host data stored in the associated page.
Referring to
The meta data generated by the memory controller 20 during the write operation is stored in the NAND memory 30 and is also needed by the memory controller 20 during the read operation. For example, the error checking bits are used by the memory controller 20 after a read operation of the host data from the NAND memory chip 30 to confirm that there are no errors in the host data read.
In the memory system 10 of the prior art, in addition to the meta data generated by the memory controller 20, meta data is also generated by the host device 12. Among the type of meta data generated by the host device 12 include the logical address and CRC of the host data etc. In the prior art, the meta data generated by the host device 12 was either stored in volatile memory (not shown), which was backed up into a non-volatile memory since a loss in power would cause the loss of such meta data, or in an external non-volatile memory 16. Typically, in the prior art, the user space is divided into space to store host data and space to store meta data. There are many ways to allocate these spaces, and all of them may cause a reduction in the space to store host data. Some approaches may cause performance degradation if two different read operations would be required to retrieve host data and its corresponding meta data separately. Or, if meta data is cached to avoid the performance degradation, a large RAM will be required, which will cause an undesirable increase in the cost of the system.
Accordingly, in the present invention, a method of operating a memory system having a host device connected to a plurality of memory devices, with each memory device having a NAND memory chip, and an associated controller is disclosed. The NAND memory chip can store a page of data in a single write operation and can read a page of data from the NAND memory in a single read operation, with the page being the smallest unit of storage and having a plurality of bits. The controller partitions each page of an associated NAND memory into a first location, a second location, and a third location. The first location is for the storage of host data. The second location is for the storage of meta data of the controller associated with the host data. The third location is for the storage of meta data of the host device associated with the host data. The host data, meta data of the controller, and meta data of the host device are written into the same page in a single write operation.
The present invention also relates to a method of reading a page of a NAND memory chip, with the page having a plurality of bits. After a page is read, the memory controller extracts from the plurality of bits a first plurality of bits of host data, a second plurality of bits of meta data for the controller associated with the NAND memory read, and a third plurality of bits of meta data for the host device.
The present invention also relates to a memory controller for controlling a non-volatile memory chip. The memory controller has a processor and a non-volatile memory for storing programming code for execution by the processor in accordance with the foregoing described method.
Finally, the present invention relates to a memory system having a host device connected to a plurality of independent memory devices, with each memory device comprising the foregoing described memory controller for controlling an associated NAND memory chip.
Referring to
The programming code stored in the non-volatile memory 122 causes the processor 124 to control the read/write of host data from/into the associated NAND memory chip 30, in accordance with the method of the present invention, as discussed hereinafter. In addition, the programming code causes the processor 124 to generate error checking codes, based upon the host data, as well as data correlating the location of the physical address in the associated NAND memory chip 30 where the data is read from or written to with the logical address (collectively “meta data”). Other meta data may also be generated by the memory controller 120. The programming code can be stored in the non-volatile memory 122, which is embedded with the processor 124 in the memory controller 120. Alternatively, the programming code can be stored in a non-volatile memory which is discrete and separate from the memory controller 120, such as within the NAND memory chip 30.
As discussed hereinabove, meta data is also generated by the host device 12 during the read or write operation. The host meta data is also supplied to the selected one of the plurality of memory controllers 120. The programming code stored in the non-volatile memory 122 also causes the processor 124 of the memory controller 120 to operate on the meta data from the host device 12. The method of reading and writing of the present invention is explained as follows:
In a write operation host data to be stored in the memory system 50 is first supplied to the host device 12. The host device 12 may choose a particular storage device 140 e.g. storage device 140(a), depending on a number of factors, such as the availability of space in that storage device 140(a), data distribution strategy, as well as other types of information. The host device 12 will also generate some information about the data, usually, in order to detect errors or recover from some types of failures. The data representing information about the data is collectively referred to as “host meta data”. The host meta data along with the host data is then supplied to the memory controller 120(a) associated with the selected storage device 140(a).
After the selected memory controller 140(a) receives the host meta data and the host data, the memory controller 120(a) will store the host meta data along with controller meta data that is generated by the controller 120 in the spare bytes of the page of the NAND memory 30 where the host data is stored. Typically, the host data stored in NAND page is protected against errors by some encoding mechanism. Thus, the host meta data, as well as the controller meta data, may also be protected by such error correction mechanisms.
In order to be able to store the host data, the associated controller meta data and the associated host meta data in the same page (including the associated spare bytes) of the NAND memory 30, it may require the host device 12 to adjust the amount of host meta data to the space available in the NAND page spare bytes, so that the entirety of the host data, and its associated controller meta data, and the associated host meta data may all fit in the same NAND page. At initial blush, this may be disadvantageous in that the amount of space for host meta data may be less than the space available to store all the host meta data. In that event, the host device 12 must decide which host meta data to store and which host meta data to discard, balancing performance with redundancy or error correction. In some cases, it may require the host meta data to be stored in the space which would otherwise be intended for the host data, thereby reducing the space for storage of host data. However, the benefit of having the host data, associated controller meta data and associated host meta data all available in a single write operation to write into the same NAND page (and subsequent read from the same NAND page) outweighs any such potential disadvantage.
When the host device 12 receives a read command it looks up its address table and selects the appropriate storage device and its associated memory controller 120.
Once the appropriate memory controller 120(a) is selected, the host device 12 communicates the read request to the selected memory controller 120(a). The memory controller 120(a) then causes a read operation to occur to read the selected page of data from the NAND chip 30(a). The selected page of data from the NAND chip 30(a) is then separated to the host data, the controller meta data and the host meta data. The memory controller 120(a) then uses the controller meta data to verify the host data. The verified host data is then passed to the host device 12, along with the host meta data.
As can be seen from the foregoing, with the method and controller and system of the present invention, read and write operations can be accomplished in a single operation with both host data and meta data collectively read from or written into a page of the NAND chip 30. Thus, performance is increased.
