Abstract:
A system and method for operating a solid state drive (SSD) within power limitations while maintaining SSD performance. In one embodiment a power management integrated circuit (PMIC) is used to measure power consumption, and a built-in self-test (BIST) procedure is used to exercise the storage device, and to calibrate the power consumed by various SSD operations. The results are stored in a power consumption cost table. In one embodiment, a procedure to dynamically adjust the power consumption cost table is employed. A power credit allocation scheme is used, along with the power consumption cost table, to track and limit the power consumed by the SSD in operation.

Description:
FIELD 
       [0001]    The following description relates to data storage and more particularly to a system and method for storing data in, and retrieving data from, a solid state drive, while maintaining the power consumption of the solid state drive within an acceptable range. 
       BACKGROUND 
       [0002]    Every day, several quintillion bytes of data may be created around the world. This data comes from everywhere: posts to social media sites, digital pictures and videos, purchase transaction records, bank transactions, sensors used to gather intelligence and data, such as climate information, cell phone GPS signal, and many others. This kind of data and its vast accumulation is often referred to as “big data.” An increasing amount of this data eventually is stored and maintained in solid-state storage drives (SSD), operated by an SSD controller, and these may reside on networks or on storage accessible via the Internet, which may be referred to as the “cloud.” This stored data may also require processing, or be subject to operations, such as read, write, erase, and/or during a search, query, encryption/decryption, compression, decompression, and other processes. These operations use power and cause a temperature increase in the SSD controller. Temperature increases in the SSD controller may degrade and slow performance in the controller. 
         [0003]    An important function of a solid state drive (SSD) controller is power management. In an SSD, throttling techniques based on a static calibration may be used as an approach to power management. This approach requires allowing power margins to account for process, voltage and temperature variations on all SSD components including regulators, dynamic read-only-memory (DRAM), NAND flash devices, and the controller itself. The drawback of this approach is that in order to guarantee adequate margin to accommodate variations throughout the product life cycle there may be a significant loss in performance. 
         [0004]    Thus, there is need for a system and method for managing power in an SSD, which provides performance near the highest performance achievable within an allocated power budget. 
       SUMMARY 
       [0005]    In one embodiment of a system and method for operating a solid state drive (SSD) within power limitations while maintaining SSD performance, a power management integrated circuit (PMIC) is used to measure power consumption, and a built-in self-test (BIST) procedure is used to exercise the storage device, and to calibrate the power consumed by various SSD operations. The results are stored in a power consumption cost table. A power credit allocation scheme is used, along with the power consumption cost table, to track and limit the power consumed by the SSD in operation. 
         [0006]    According to an embodiment of the present invention there is provided a system for power management in a solid state drive (SSD) including a flash memory, the system including: a controller; and a power management integrated circuit (PMIC), the controller configured to receive commands, each command corresponding to a requested read operation, a requested write operation, or a requested erase operation to be dispatched to the flash memory, the controller configured to place each command in the command queue, and to dispatch each command from the command queue to the flash memory, according to an algorithm, so as to maintain a power consumption of the solid state drive below a maximum acceptable power consumption value, the algorithm employing a power consumption cost table, the controller configured to dynamically adjust the power consumption cost table based on information received from the PMIC. 
         [0007]    In one embodiment, the controller is configured to dynamically adjust the power consumption cost table by: performing a built-in-self-test (BIST) procedure including: a plurality of test read operations; a plurality of test write operations; and a plurality of test erase operations; and measuring the power consumed by the performing of the plurality of test read operations, the plurality of test write operations, and the plurality of test erase operations. 
         [0008]    In one embodiment, the controller is configured to dynamically adjust the power consumption cost table prior to initial operation of the SSD. 
         [0009]    In one embodiment, the controller is configured to dynamically adjust the power consumption cost table by correlating, during operation of the solid state drive, power consumption data from the PMIC with a frequency to simultaneously perform read operations, write operations, and erase operations. 
         [0010]    In one embodiment, the controller is configured to dynamically adjust the power consumption cost table only when the power consumption of the solid state drive exceeds a threshold fraction of the maximum acceptable power consumption value. 
         [0011]    In one embodiment, the threshold fraction is 50%. 
         [0012]    In one embodiment, the controller includes a flash manager. 
         [0013]    In one embodiment, the controller includes a central processing unit (CPU). 
         [0014]    In one embodiment, the algorithm includes: forming a pool containing a quantity of credits proportional to the maximum acceptable power consumption value; removing a first quantity of credits from the pool for each write operation conducted, at the beginning of the write operation, and replacing the first quantity of credits at the completion of the write operation, the first quantity of credits being proportional to a mean power consumption of a write operation; removing a second quantity of credits from the pool for each read operation conducted, at the beginning of the read operation, and replacing the second quantity of credits at the completion of the read operation, the second quantity of credits being proportional to a mean power consumption of a read operation; removing a third quantity of credits from the pool for each erase operation conducted, at the beginning of the erase operation, and replacing the third quantity of credits at the completion of the erase operation, the third quantity of credits being proportional to a mean power consumption of an erase operation, the mean power consumption of the write operation, the mean power consumption of the read operation, and the mean power consumption of the erase operation being determined from the power consumption cost table; and delaying a command in the command queue when there are insufficient credits in the pool for the command. 
         [0015]    According to an embodiment of the present invention there is provided a method for operating a solid state drive including a controller, a flash memory, and a power management integrated circuit (PMIC), the method including: receiving commands, each command corresponding to a requested read operation, a requested write operation, or a requested erase operation to be executed in the flash memory; placing each command in a command queue; dispatching each command from the command queue to the flash memory, according to an algorithm, so as to maintain a power consumption of the solid state drive below a maximum acceptable power consumption value, the algorithm employing a power consumption cost table; and dynamically adjusting, by the controller, the power consumption cost table based on information received from the PMIC. 
         [0016]    In one embodiment, the method includes dynamically adjusting, by the controller, the power consumption cost table prior to initial operation of the solid state drive. 
         [0017]    In one embodiment, the dynamically adjusting, by the controller, of the power consumption cost table includes: performing, under the control of the controller executing a built-in-self-test (BIST) procedure, a plurality of test read operations, a plurality of test write operations, and a plurality of test erase operations; and measuring the power consumed by the performing of the plurality of test read operations, the plurality of test write operations, and the plurality of test erase operations. 
         [0018]    In one embodiment, the measuring of the power consumed by the performing of the plurality of test read operations, the plurality of test write operations, and the plurality of test erase operations includes measuring, by a power management integrated circuit (PMIC), the power consumed by the performing of the plurality of test read operations, the plurality of test write operations, and the plurality of test erase operations. 
         [0019]    In one embodiment, the method includes forming a pool containing a quantity of credits proportional to the maximum acceptable power consumption value; removing a first quantity of credits from the pool for each write operation conducted, at the beginning of the write operation, and replacing the first quantity of credits at the completion of the write operation, the first quantity of credits being proportional to a mean power consumption of a write operation; removing a second quantity of credits from the pool for each read operation conducted, at the beginning of the read operation, and replacing the second quantity of credits at the completion of the read operation, the second quantity of credits being proportional to a mean power consumption of a read operation; removing a third quantity of credits from the pool for each erase operation conducted, at the beginning of the erase operation, and replacing the third quantity of credits at the completion of the erase operation, the third quantity of credits being proportional to a mean power consumption of an erase operation, the mean power consumption of the write operation, the mean power consumption of the read operation, and the mean power consumption of the erase operation being determined from the power consumption cost table; and delaying a command in the command queue when there are insufficient credits in the pool for the command. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    These and other features and advantages of the present invention will be appreciated and understood with reference to the specification, claims and appended drawings wherein: 
           [0021]      FIG. 1  is a block diagram of a related art server in communication with a storage node; 
           [0022]      FIG. 2  is a block diagram of a server in communication with a storage node according to an embodiment of the present invention; 
           [0023]      FIG. 3  is a block diagram of a solid state drive processing unit in communication with a flash memory according to an embodiment of the present invention; and 
           [0024]      FIG. 4  is a flow chart of a method for operating a solid state drive according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments of a system and method for dynamic self-correcting power management for solid state drive provided in accordance with the present invention and is not intended to represent the only forms in which the present invention may be constructed or utilized. The description sets forth the features of the present invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and structures may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. As denoted elsewhere herein, like element numbers are intended to indicate like elements or features. 
         [0026]      FIG. 1  is a block diagram of a related art system which includes a server  110  and a storage node, such as an SSD  130 , for performing data queries according to prior art implementations. The SSD  130  may be a part of the server  110 , or it may be separate from, and in communication with, the server  110 , as illustrated in  FIG. 1 . The server  110  may include a processor, such as a server central processing unit (CPU)  120 . The SSD  130  may include an SSD controller  140  and a flash memory  150 . The server  110  and the SSD  130  may be implemented in a cloud-based computing environment. The server  110  and the SSD  130  may communicate using a suitable bus such as Peripheral Component Interconnect Express (PCIe), running a suitable protocol. 
         [0027]    As used herein, the phrase “in communication with” refers to direct communication, or indirect communication, via one or more components named or unnamed herein. The server  110  and the SSD  130  can be in communication with each other via a wired or wireless connection. For example, in one embodiment, the SSD  130  may comprise pins (or a socket) to mate with a corresponding socket (or pins) on the server  110  to establish an electrical and physical connection. In another embodiment, the SSD  130  can comprise a wireless transceiver to place the server  110  and the SSD  130  in wireless communication with each other. The server  110  and the SSD  130  may be separately housed from each other, or contained in the same housing. Referring to  FIG. 2 , in one embodiment, an SSD processing unit  240  may be used as an SSD controller  140 , the SSD processing unit  240  being a smart controller having greater processing capability than a conventional SSD controller. In this embodiment, the SSD processing unit  240  is an example of an SSD controller  140 . 
         [0028]    Referring to  FIG. 3 , the SSD processing unit  240  includes, in one embodiment, a host interface  300 , a microcontroller  310 , which may also be referred to as a central processing unit (CPU), a hardware engine  320 , a processing unit buffer  360 , and a flash interface  340 . The host interface  300  may be, for example, PCIe, NVMe, SATA, Fibre Channel, SAS, SCSI over PCIe, or Ethernet. Other components, such as additional buffers, may also be present in the processing unit  240 . The SSD processing unit  240  communicates with the flash memory  150  through the flash interface  340 , which may implement a flash channel interface. In one embodiment, there is a separate hardware engine  320  for each flash channel. The SSD processing unit  240  may be a single silicon chip, e.g., a system on a chip (SOC). In one embodiment, the microcontroller  310 , the processing unit buffer  360 , and the flash interface  340  are all integrated onto a single semiconductor chip (e.g., a single silicon chip), along with a hardware engine  320 . The SSD processing unit  240  may include specialized hardware, firmware, or software, referred to as a flash manager, dedicated to managing the operation of the flash memory for high performance while respecting constraints on power consumption, according to embodiments of the present invention. In one embodiment the processing unit  240  contains a power management integrated circuit (PMIC)  370 , which performs power-related functions, such as monitoring the dynamic current draw or power consumption of the SSD. The PMIC may be embedded in the SSD processing unit  240  or it may be a separate component in the SSD  130 . The SSD  130  may also contain a temperature sensor  375 , which may be embedded in the SSD processing unit  240  as shown, or which may be a separate component in the SSD  130 . 
         [0029]    In operation, a significant portion of the power used by the SSD  130  may be used to perform flash operations, including read operations, erase operations, and write operations. Several flash operations may be conducted, i.e., active, simultaneously under the control of the SSD processing unit  240 , and the instantaneous power consumption at any time, due to the flash operations, may be the sum, over all flash operations active at that time, of the power consumed by each flash operation. 
         [0030]    In operation, it may be unacceptable for an SSD  130  to exceed its maximum acceptable power consumption value, i.e., the maximum power the power system is capable of delivering to the SSD without risk of shutdown, malfunction, or failure. Exceeding the maximum acceptable power consumption value may be avoided by throttling the SSD  130 , i.e., limiting the rate at which flash operations are performed so as to limit the power consumed. Throttling slows the operation of the SSD  130 , and it is therefore advantageous to use no more throttling than necessary. To this end, it is advantageous to employ an accurate model of the power consumed by flash operations. Such a model may be implemented as a table, referred to as a power consumption cost table. The power consumption cost table may for example list the power consumed by each kind of flash operation, as a function of the temperature of the SSD. 
         [0031]    In one embodiment, a power consumption cost table is initially created in a pre-production phase, when the SSD is designed or when a prototype unit is tested. A design may be simulated numerically, or power consumption values may be obtained from specifications provided by the manufacturer of a flash memory  150  used in the SSD  130 . Alternatively, or in addition, a prototype unit may be instrumented with a power-measuring device, and its power consumption in operation may be measured. This pre-production calibration is performed for each drive type or design, which may have characteristics depending on, e.g., the format factor or flash type. 
         [0032]    Another characterization of the power consumption may be performed during or after production and may be used to improve a power consumption cost table developed in pre-production. In one embodiment, this is accomplished using a power management integrated circuit (PMIC)  370 , together with a built-in self-test (BIST) procedure, which is executed by the SSD processing unit  240 . The BIST performs a pattern of one or more read operations, one or more write operations, and one or more erase operations in the flash memory  150 , and, during these operations, the PMIC measures the power consumed, and reports the results to the SSD processing unit  240 . The SSD processing unit  240  then calculates the power consumed by each type of flash operation and saves the results in the power consumption cost table. In one embodiment, this process is performed in manufacturing, for each SSD  130  manufactured, after the SSD  130  is assembled and before the SSD  130  is shipped. In other embodiments it is instead, or also, performed at other times in the life of the SSD  130 , such as at startup. 
         [0033]    The power consumption of various flash operations may change over time, e.g., as the temperature of the SSD  130  changes or as the flash memory  150  ages, and in one embodiment the power consumption cost table is adjusted as needed to avoid exceeding the maximum acceptable power consumption value, while also avoiding more throttling than necessary. In particular, one or more power consumption thresholds are used by the SSD processing unit  240  to trigger checking and, if necessary, adjusting of the power consumption cost table. For example, a threshold is set at a value of 0.5 times the maximum acceptable power consumption value. When the PMIC  370  reports an instantaneous power consumption equal to or exceeding this threshold, the SSD processing unit  240  checks and, if necessary, adjusts the values stored in the power consumption cost table. 
         [0034]    In one embodiment, checking and adjusting of the values stored in the power consumption cost table proceeds as follows. The processing unit  240  calculates the expected instantaneous power consumption using the number of active flash operations of each kind and the value, from the power consumption cost table, of the expected power consumption for each. If there is a significant discrepancy between the instantaneous power consumption reported by the PMIC  370  and the expected instantaneous power consumption calculated by the SSD processing unit  240 , then the SSD processing unit  240  initiates a procedure to dynamically adjust the power consumption cost table. This may involve re-running the BIST, or it may involve monitoring the number of active read operations, the number of active erase operations, and the number of active write operations, as well as the total power consumption reported by the PMIC  370 , for some period of time, and inferring, from these observations, corrected values for the power consumption cost table. 
         [0035]    During this process, if the power consumption cost table is configured to store power consumption data as a function of temperature, the SSD processing unit  240  may store measured results for the power consumption at the current operating temperature, as measured by the temperature sensor  375 , and the SSD processing unit  240  may generate data for temperatures other than the current operating temperature by a number of methods, including but not limited to curve fitting using previously obtained data at other temperatures, and extrapolation using models for the expected dependence on temperature of the power consumption of each flash operation. 
         [0036]    In operation, throttling of the SSD  130  based on a power consumption cost table, to avoid exceeding the maximum acceptable power consumption value, may be accomplished using a method based on power credits. In one embodiment, the SSD processing unit  240  creates, at startup, a pool of credits proportional to the maximum acceptable power consumption value. This pool may for example be a number in a register or in memory, initialized and subsequently updated by the SSD processing unit  240 . After the pool of credits is initialized, the SSD processing unit  240  removes from the pool a number of credits for each flash operation initiated, and returns the credits to the pool once the flash operation is complete. The number of credits removed for each flash operation bears the same proportion to the initial size of the pool of credits as the power consumed by the flash operations bears to the maximum acceptable power consumption value. As a result, the number of credits remaining in the pool of credits is proportional, at any time, to the power reserve. In one embodiment, the number of credits remaining in the pool of credits is used to trigger checking and, if necessary, adjusting of the power consumption cost table. A pool credit threshold may be set at some value, e.g., at 50% of the initial size of the pool of credits; when the number of credits in the pool falls below this threshold value, the SSD processing unit  240  initiates checking and, if necessary, adjusting of the power consumption cost table. 
         [0037]    In one embodiment, the number of credits remaining in the pool of credits is used as part of a throttling strategy to maintain the power consumption of the solid state drive below a maximum acceptable power consumption value. Commands corresponding to read, erase, and write operations to be performed are placed in a command queue and each command is dispatched to the flash memory only when the number of credits in the pool is sufficient to support the operation. For example, if there are 60 credits in the pool of credits, if the next command in the command queue is an erase operation, and if, according to the power consumption cost table, an erase operation requires 100 credits, then the SSD processing unit  240  will delay the command in the command queue, i.e., the SSD processing unit  240  will not dispatch the command to the flash memory, until enough credits have been returned to the pool of credits that 100 credits are available to execute the erase operation. If the SSD  130  contains a temperature sensor  375 , then each retrieval of data from the power consumption cost table may use the current operating temperature of the SSD  130  to identify the relevant entry in the power consumption cost table. 
         [0038]      FIG. 4  illustrates a method for dynamic self-correcting power management in a solid state drive, according to embodiments of the present invention. At act  402 , the SSD  130  is calibrated for power management. Calibration may be performed in pre-production or after production of the SSD  130 , or both. At act  414 , the SSD  130  receives commands, corresponding to flash operations, such as read, write, or erase, to be performed by the SSD  130 . Each operation on the SSD  130  is assigned a number of credits proportional to the power consumption of the operation, which is estimated from the power consumption cost table. In an act  416 , the SSD processing unit  240  adjusts the number of credits remaining in the pool of credits for the SSD  130  by the number of credits assigned to each operation dispatched to flash memory  150 . 
         [0039]    At act  418 , if the number of credits in the pool of credits is above the threshold for checking and, if necessary, adjusting of the power consumption cost table, the process returns to act  414 . However if, at act  418 , the number of credits in the pool of credits is determined to have fallen below the threshold for checking and, if necessary, adjusting of the power consumption cost table, the process proceeds to act  420 . In act  420 , the SSD processing unit  240  checks and, if necessary, adjusts the values stored in the power consumption cost table. The process then returns to act  414 . 
         [0040]    Several alternatives may be used with these embodiments. For example, while solid state drives (SSDs) are discussed in examples above, any type of suitable memory device, such as a hard disk drive (HDD), can be used. Further, embodiments of the present invention may be used in a redundant array of independent disks (RAID) to achieve similar advantages in optimizing performance and resource utilization. 
         [0041]    Other embodiments are within the scope and spirit of the invention. For example, the functionality described above can be implemented using software, hardware, firmware, hardwiring, or combinations of any of these. One or more computer processors operating in accordance with instructions may implement the functions associated with managing the use of storage devices in accordance with embodiments of the present invention. If such is the case, it is within the scope of the present disclosure that such instructions may be stored on one or more non-transitory processor readable storage media (e.g., a magnetic disk, non-volatile random-access memory, phase-change memory or other storage medium). Additionally, software or firmware modules implementing functions used by embodiments of the present invention may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Accordingly, it is to be understood that a system and method for dynamic self-correcting power management for solid state drive constructed according to principles of this invention may be embodied other than as specifically described herein. The invention is also defined in the following claims, and equivalents thereof.