Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1999-08-09
2002-01-01
Yoo, Do Hyun (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S161000, C714S006130, C365S228000
Reexamination Certificate
active
06336174
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to memory backup and restoration of digital information, and more particularly, to a hardware assisted memory backup system and method using nonvolatile memory.
BACKGROUND OF THE INVENTION
The need for emerging file server technology with multi-protocol file system semantics has created unique problems in data management for file service operations, such as saving data to disk storage in real-time and reliably. These problems are further exacerbated by the potential of catastrophic system failures, such as operating system (O/S) hang-up, and/or unexpected power failures and system resets. For some applications, the loss of certain types of data may not pose any serious problems. For client/server applications, however, if the system loses “meta” data, i.e., information concerning a system's file structure, the file structure will be difficult, if not impossible, to reconstruct.
In a typical client/server application, a client computer can request a server computer to store file system data to a permanent storage device, such as a hard disk. Because a typical write transaction can take several operations to complete, the client data is temporarily stored in server memory until the write transaction is successfully completed. Once the data is safely stored to disk, the server computer can inform the client computer that the write transaction was completed. This entire store transaction can take as long as 20 milliseconds, which is a long delay for the client.
Unfortunately, if a catastrophic event occurs while all or some of the data is still in system memory, data loss can occur. Data loss occurs because the server system memory typically is volatile memory, such as Dynamic Random Access Memory (DRAM) or Static Random Access Memory (SRAM). For example, DRAM employs a system of transistors and capacitors to retain data. Because the capacitors cannot maintain an electrical charge indefinitely, the capacitors must be continuously refreshed by a power supply. Thus, backing-up data stored in DRAM in the event of a power failure presents the additional problem of refreshing DRAM until all data has been safely transferred to nonvolatile memory.
Some conventional systems automatically transfer data from volatile memory (e.g., SRAM) to nonvolatile memory (e.g., Electrical Erasable Programmable Read-only Memory (EEPROM)), if the chip power drops below a first predetermined voltage (e.g., 4.2 volts from 5 volts). If the chip power drops below the first predetermined voltage, a store operation is started that continues until the chip power drops below a second predetermined voltage (e.g., 3.5 volts), after which time the integrity of the data being transferred from volatile memory becomes uncertain. Thus, the store operation must complete before the chip power drops below the second predetermined voltage.
The conventional systems described above provide a solution for systems requiring a limited amount of data transfer, such as 32K. Unfortunately, the amount of data that can be safely transferred by these systems is limited by the finite interval of time where the chip power is sufficiently high to ensure a successful data transfer. Unfortunately, for systems requiring a larger data transfer, such as 8 Mb or more, these conventional systems do not provide a solution. Moreover, these systems typically cannot operate with DRAM because they do not provide a refresh engine that can operate during power failure events. As discussed above, a refresh engine, or its equivalent, is necessary in DRAM based systems to maintain data stored in volatile memory while such data is being backed-up to nonvolatile memory.
An additional problem with some conventional systems is their inability to provide memory backup in response to events other than power failure events, such as unexpected system resets or O/S hang-up. The conventional systems are unable to differentiate between normal system shutdowns and unexpected system shutdowns initiated by, for example, a user pressing a hardware reset button. The inability to differentiate between normal and unexpected system shutdowns can decrease the life of the nonvolatile memory employed in such systems because of the finite number of write cycles available in such memories. The ability to prolong the “write” life of nonvolatile memory is important when one considers that a typical EEPROM cell or flash memory cell can break down after a finite number of write cycles.
Still another problem with conventional systems and methods is how such systems and methods store O/S kernel code for rebooting the system after a catastrophic failure. In conventional embedded systems, O/S kernel code is usually stored in specialized nonvolatile memory, which requires additional memory mapping, and modification of BIOS to load and initialize the kernel. Storing O/S kernel code in specialized nonvolatile memory typically increases the number of system components, increases BIOS development and maintenance efforts, and reduces system boot speed.
Accordingly, there remains a need for a memory backup system and method that copies digital information from volatile memory to nonvolatile memory in response to catastrophic events, such as O/S hang-up and unexpected power failures and system resets. The system and method should be able to quickly copy a relatively large amount of information (e.g., 8 Mb or greater) from volatile memory (e.g., DRAM) to nonvolatile memory without corrupting the integrity of the information. Moreover, the system and method should be able to differentiate between normal system shutdown events and unexpected shutdown events to preserve the “write” life of the nonvolatile memory. The system and method should also use conventional memory chip formats and packaging, such as Dual In-line Memory Module (DIMM) or Single In-line Memory Module (SIMM). These conventional package formats can enable the system to easily couple with the system memory bus of a conventional computer system, such as a Personal Computer (PC).
Additionally, there is a need for storing O/S kernel code into main system memory to reduce the number of system components, reduce BIOS development and maintenance efforts, and improve system boot speed.
SUMMARY OF THE INVENTION
The present invention is directed to a hardware assisted memory module (HAMM) for communicating digital information between volatile and nonvolatile memory in response to a trigger event from, for example, a host computer system. The HAMM generally includes a volatile memory coupled to an information source for receiving and storing information; a nonvolatile memory coupled to the volatile memory for receiving and storing information communicated from the volatile memory; and a controller coupled to the memories for controlling the communication of information between the memories in response to the trigger event. The controller can determine the type of the trigger event from, for example, control information stored in the volatile memory.
In a preferred embodiment of the present invention, the HAMM is coupled to a host computer system, such as a PC. During normal operation of the computer system, the HAMM behaves like a conventional memory module, for example, storing digital information received from a data bus. The HAMM, however, detects and responds with a memory backup operation to at least one of the following events: 1) unexpected power failure, 2) operating system hang-up, or 3) unexpected system reset. Upon detection of an event, the HAMM electronically isolates itself from the host computer system before copying the digital information from volatile memory to nonvolatile memory. Once isolated the HAMM takes its power from an auxiliary power supply, such as a battery.
The HAMM can be configured to copy all or part of the digital information to nonvolatile memory. Upon either a request or at power-up, the HAMM copies the digital information from nonvolatile memory into volatile memory. If there is a normal or expected computer shutdown, the O/S warns the HAMM before shutti
Li Qiang
Strang, Jr. Clifford E.
Zahornacky Jon F.
Maxtor Corporation
Moazzami Nasser
Sigmond David M.
Yoo Do Hyun
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