Source: https://patents.justia.com/patent/10283205
Timestamp: 2019-11-20 06:33:32
Document Index: 129237046

Matched Legal Cases: ['art 700', 'art 700', 'art 700', 'art 700', 'art 700', 'art 700', 'art 700', 'art 700', 'art 700', 'art 700']

US Patent for Preemptive idle time read scans Patent (Patent # 10,283,205 issued May 7, 2019) - Justia Patents Search
Justia Patents Loading Initialization Program (e.g., Booting, Rebooting, Warm Booting, Remote Booting, Bios, Initial Program Load (ipl), Bootstrapping)US Patent for Preemptive idle time read scans Patent (Patent # 10,283,205)
Sep 30, 2017 - Micron Technology, Inc.
Devices and techniques for initiating and controlling preemptive idle time read scans in a flash based storage system are disclosed. In an example, a memory device includes a NAND memory array and a memory controller to schedule and initiate read scans among multiple locations of the memory array, with such read scans being preemptively triggered during an idle (background) state of the memory device, thus reducing host latency during read and write operations in an active (foreground) state of the memory device. In an example, the optimization technique includes scheduling a read scan operation, monitoring an active or idle state of host IO operations, and preemptively initiating the read scan operation when entering an idle state, before the read scan operation is scheduled to occur. In further examples, the read scan may preemptively occur based on time-based scheduling, frequency-based conditions, or event-driven conditions triggering the read scan.
This application is a U.S. National Stage Application under 35 U.S.C. 371 from International Application No. PCT/CN2017/104945, filed Sep. 30, 2017, which is incorporated herein by reference in its entirety.
Non-volatile memory can retain stored data when not powered, and includes flash memory, read-only memory (ROM), electrically erasable programmable ROM (EEPROM), static RAM (SRAM), erasable programmable ROM (EPROM), resistance variable memory, such as phase-change random-access memory (PCRAM), resistive random-access memory (RRAM), magnetoresistive random-access memory (MRAM), or 3D XPoint™ memory, among others.
Such 3D NAND devices often include strings of storage cells, coupled in series (e.g., drain to source), between one or more source-side select gates (SGSs) proximate a source, and one or more drain-side select gates (SGDs) proximate a bit line. In an example, the SGSs or the SGDs can include one or more field-effect transistors (FETs) or metal-oxide semiconductor (MOS) structure devices, etc. In some examples, the strings will extend vertically, through multiple vertically spaced tiers containing respective word lines. A semiconductor structure (e.g., a polysilicon structure) may extend adjacent a string of storage cells to form a channel for the storages cells of the string. In the example of a vertical string, the polysilicon structure may be in the form of a vertically extending pillar. In some examples the string may be “folded,” and thus arranged relative to a U-shaped pillar. In other examples, multiple vertical structures may be stacked upon one another to form stacked arrays of storage cell strings.
In NAND flash based storage systems, the read voltage threshold (Vt) that is required to successfully perform read operations is constantly subjected to shifts. These shifts may occur due to well-known stresses on the NAND flash such as Read Disturb, Data Retention, Cross-temperature effect, among other conditions. Further, different NAND blocks within a memory array may experience a varying amount of stress that induces a varying amount of charge loss or charge gain; likewise, different NAND blocks of a memory array are often written and read at different temperatures. As a result, a mismatch between the NAND Vt and the read voltage actually used by a storage system occur in many scenarios, and techniques for read voltage calibration are used by NAND storage systems to adjust the read voltage in accordance with NAND Vt.
Existing approaches for tracking the NAND health and the corresponding Vt changes include tracking a raw bit error rate (RBER) trend, such as a RBER trend determined from reading pages in NAND blocks with a read scan. The objective of performing read scans is to provide real time NAND RBER feedback, such that the system can optimally calibrate NAND read voltages to minimize error handling trigger rate, or initiate pre-emptive action to mitigate data integrity risk induced by various stress factors in the NAND blocks. However, performing read scans often imposes a performance overhead for the storage system, and increases host command latency.
FIG. 5 illustrates a block diagram of an example system including a memory device adapted for implementing preemptive idle time read scan operations.
FIG. 6A illustrates a timeline of an example read scan trigger criteria implementing time-based condition triggers for preemptive idle time read scan operations in a memory device.
FIG. 6B illustrates a timeline of an example read scan trigger criteria implementing event-based condition triggers for preemptive idle time read scan operations in a memory device.
FIG. 7 illustrates a flowchart of an example set of operations adapted for performing preemptive idle time read scan operations in a memory device.
The systems, processes, and configurations discussed herein relate to optimization techniques for triggering and performing preemptive idle time read scans in a NAND memory device. Specifically, example techniques are disclosed that use window-based criteria, instead of absolute criteria, to preemptively trigger read scans when applicable during idle states of host read/write drive activity. The performance of read scans during such idle states may reduce the impact of read scans on host read/write performance. Further, example techniques are disclosed that enable the window-based trigger criteria to be used in response to time triggers, frequency-based triggers, or event-based triggers. Still further, the preemptive read scan triggers may be used to provide a memory system with the opportunity to perform additional maintenance tasks in the background during idle states, thus alleviating the host IO performance impact of conducting such maintenance tasks in the foreground.
One or more communication interfaces can be used to transfer data between the memory device 110 and one or more other components of the host device 105, such as a Serial Advanced Technology Attachment (SATA) interface, a Peripheral Component Interconnect Express (PCIe) interface, a Universal Serial Bus (USB) interface, a Universal Flash Storage (UFS) interface, an eMMC™ interface, or one or more other connectors or interfaces. The host device 105 can include a host system, an electronic device, a processor, a memory card reader, or one or more other electronic devices external to the memory device 110. In some examples, the host 105 may be a machine having some portion, or all, of the components discussed in reference to the machine 800 of FIG. 8.
Each memory cell in the memory array 200 includes a control gate (CG) coupled to (e.g., electrically or otherwise operatively connected to) an access line (e.g., word lines (WL) WL00-WL70 210A-217A, WL01-WL71 210B-217B, etc.), which collectively couples the control gates (CGs) across a specific tier, or a portion of a tier, as desired. Specific tiers in the 3D memory array, and accordingly, specific memory cells in a string, can be accessed or controlled using respective access lines. Groups of select gates can be accessed using various select lines. For example, first-third A0 SGD 226A0-228A0 can be accessed using an A0 SGD line SGDA0 225A0, first-third An SGD 226An-228An can be accessed using an An SGD line SGDA 225Ar, first-third B0 SGD 226B0-228B0 can be accessed using an B0 SGD line SGDB0 225B, and first-third Bn SGD 226Bn-228Bn can be accessed using an Bn SGD line SGDBn 225Bn. First-third A0 SGS 231A0-233A0 and first-third An SGS 231A-233An can be accessed using a gate select line SGS0 230A, and first-third B0 SGS 231B0-233B0 and first-third Bn SGS 231Bn-233Bn can be accessed using a gate select line SGS1 230B.
As an example, if a programming voltage (e.g., 15V or more) is applied 20 to a specific word line, such as WL4, a pass voltage of 10V can be applied to one or more other word lines, such as WL3, WL5, etc., to inhibit programming of non-targeted memory cells, or to retain the values stored on such memory cells not targeted for programming. As the distance between an applied program voltage and the non-targeted memory cells increases, the pass voltage required to refrain from programming the non-targeted memory cells can decrease. For example, where a programming voltage of 15V is applied to WL4, a pass voltage of 10V can be applied to WL3 and WL5, a pass voltage of 8V can be applied to WL2 and WL6, a pass voltage of 7V can be applied to WL1 and WL7, etc. In other examples, the pass voltages, or number of word lines, etc., can be higher or lower, or more or less.
The following techniques and configurations provide techniques implemented within a NAND memory device for aspects of read scan optimization, including scheduling, triggering, and control of such read scan operations. The techniques and configurations discussed herein may be specifically applicable to a 3D NAND flash based storage system, such as a system embodying the 3D NAND architecture features discussed above. However, it will be apparent that the disclosed read scan optimization techniques and configurations may also apply to other forms of NAND flash devices, including with components of NAND flash devices applied in other form factors or arrangements.
In NAND flash based storage systems, a NAND memory array includes various blocks that experience different amount of charge loss and charge gain, and various blocks that are programmed (written) at different temperatures. Thus, the Vt to read any particular block or area of the memory array may vary from another block or another area of the memory array. Further, the Vt for a particular block or area of memory is constantly subjected to shifts due to stresses, and as a result, Vt may shift in either direction.
Read disturb is an example of a stress occurring on a NAND flash device that affects Vt. As a host or application retrieves certain data from the flash device, the read disturb stress may build up if the host utilizes a particularly high read rate or read intensive application of data (depending on how the data is scattered within the flash device). For instance, if a logical block address (LBA) maps to a particular physical location of a NAND block, because of the biasing condition within the block, stresses may be induced on the unselected word lines that cause the Vt of the memory cells to shift.
Cross-temperature effect is another example of a stress occurring on a NAND flash device that affects Vt. Cross-temperature effect causes a shift in the cell Vt in the NAND blocks, to the right or left, as a result of a temperature difference between the time of writing and the time of reading. For instance, as data is written to a NAND flash device (e.g., a SSD drive, or SD/MMC card), the Vt needed to read the data is based on the ambient temperature when the data was is written. However, because the data may remain resident on the flash device for long period of time, the flash device is less likely to be read at the same temperature.
A mismatch between a read voltage used to read a block and the Vt for a particular block will result in data errors. One representation of data errors, the fail bit count, may be measured in a NAND storage system as a “raw bit error rate” (RBER). As a result, RBER provides a function of the mismatch between the read voltage and the Vt. Thus, in the operation of many existing NAND flash-based storage systems, the RBER provides a measurement to determine whether read voltage is incorrect, and whether voltage calibration should be conducted.
NAND health, as indicated by a trend or measurement of RBER, can be tracked by reading pages from various blocks of the NAND memory array. This technique for reading pages is commonly referred to as a “read scan”, and involves reading a random or determined set of sampled pages or word lines at different read voltages across NAND blocks. In existing memory devices, a read scan may be triggered at a regular cadence from synchronous events to track time-dependent stress effects such as data retention; or, a read scan may be triggered based on block usage or host workload pattern from asynchronous events, such as in case of read disturb.
The primary objective of read scans is to provide real time NAND RBER feedback, such that the memory device determines when to calibrate NAND read voltages to minimize error handling trigger rate, or when to initiate preemptive action to mitigate data integrity risk induced by various stress factors in the NAND blocks. With existing forms of read scan processes, sampling the RBER at different read voltages impacts host performance and increases command latency. Thus, the sampling used by existing forms of read scan processes is often performed at a slow enough rate so that the host performance is not impacted.
Techniques and configurations are discussed herein to improve the system performance by coordinating with scheduled conditions, such as time window-based, frequency-based, or event-based conditions, to pre-emptively trigger read scans during host IO idle time. This provides an opportunity for a memory system to reduce host IO contentions in the foreground based on absolute triggers of the scheduled conditions, and thus improve performance and reduce latency for host operations under benchmark workloads and typical user workloads.
The techniques discussed herein include the use of window-based criteria in lieu of absolute criteria to preemptively trigger read scans in idle periods of memory device activity. In particular, memory devices used in mobile devices and consumer SSDs typically experience a bursty workload characterized by frequent host idle times that allow the memory system firmware to perform background tasks such as read scans. The read scan management techniques discussed herein allow memory device firmware to effectively execute read scans during host idle events and reduce the impact on host performance.
In the examples discussed herein, the window-based criteria may be applied to time triggers, frequency domain triggers, or event based triggers, to allow deployment in response to synchronous and asynchronous events of the memory device. When the window-based trigger criteria is met, the memory device initiates read scans on the sampled NAND blocks as a background task during the next host idle state. The read scan then may be provided with an opportunity to complete upon occurrence of the idle state, in a preemptive fashion, before a scheduled condition that launches the read scan would otherwise occur.
This preemptive read scan provides an opportunity for the memory device to perform data integrity specific maintenance tasks in the background during host idle time, thus alleviating the host IO performance impact of running in the foreground. As a result, collisions or contentions between host IO accesses and read scans in the foreground may be minimized. Also as a result, the memory device may utilize the identified host idle time to conduct read scans and other background tasks in an optimized or prioritized manner, to provide improved host IO performance and latency for typical usage of mobile devices and consumer SSDs. This approach is complimentary to the various low power requirements found in some mobile devices and consumer SSDs, which often impose aggressive power management policies on memory devices that tend to limit the availability of background idle time.
The techniques discussed herein also may be used to effectively hide latencies caused by read scans in the background host idle time. The techniques also help to minimize read scan related collisions with host IO in the foreground, thus improving performance and reducing latency overheads for memory device read/write operations. Additionally, the techniques provide better performance and latency consistency for benchmark workloads, as well as optimization for typical user workloads that are characterized with frequent host idle times. These and other technical advantages will be apparent from the following example configurations and implementations.
FIG. 5 provides a block diagram of an example system 500 including a memory device 510 (e.g., a SSD storage device, a SD/MMC card, etc.) having a memory controller 540 with control modules 542 adapted for implementing the read scan optimization techniques discussed herein. In an example, the functionality of the control modules 542 may be implemented in respective modules in a firmware of the memory controller 540. However, it will be understood that various forms of software, firmware, and hardware may be utilized to by the controller 540 to implement the control modules 542 and the other techniques discussed herein.
As shown, the memory device 510 includes a NAND memory array 530 with multiple dies (dies 1-N), with each die including one or more blocks (blocks 1-N). Each of the one or more blocks may include further divided portions, such as one or more word lines (not shown) per block; and each of the one or more word lines may be further comprised of one or more pages (not shown) per word line, depending on the number of data states that the memory cells of that word line are configured to store.
In an example, the blocks of memory cells of the memory array 530 include groups of at least one of: single-level cell (SLC), multi-layer cell (MLC), triple-layer cell (TLC), or quad-layer cell (QLC) NAND memory cells. Also, in an example, the memory array 530 is arranged into a stack of three-dimensional (3D) NAND dies, such that the respective group of multiple blocks hosting a respective block is a member of a group of blocks provided by a respective die in the stack of 3D NAND dies. These configurations and further detailed components of the memory array 530 are not illustrated in FIG. 5 for simplicity. However, the memory array 530 may incorporate these or any of the features described above with reference to features of 3D NAND architecture devices or other forms of NAND storage devices.
The memory device 510 is shown as being operably coupled to a host 520 via a controller 540. The controller 540 is adapted to receive and process host IO commands 525, such as read operations, write operations, erase operations, and the like, to read, write, erase, and manage data stored within the memory array 530. A variety of other components for the memory device 510 (such as a memory manager, and other circuitry or operational components) and the controller 540 are also not depicted for simplicity.
The controller 540 is depicted as including a memory 544 (e.g., volatile memory), processing circuitry 546 (e.g., a microprocessor), and a storage media 548 (e.g., non-volatile memory), used for executing instructions (e.g., instructions hosted by the storage media 548, loaded into memory 544, and executed by the processing circuitry 546) to implement the control modules 542 for management and use of the memory array 530. The functionality provided by the control modules 542 may include, but is not limited to: IO operation monitoring 550 (e.g., to monitor read and write IO operations, originating from host commands); host operation processing 555 (e.g., to interpret and process the host IO commands 525, and to issue further commands to the memory array 530 to perform respective read, write, erase, or other host-initiated operations); read scan control 560 (e.g., to control the timing, criteria, conditions, and parameters of respective read scan operations 585 on the memory array 530); read voltage control 570 (e.g., to establish, set, and utilize a read voltage level to read a particular portion of the memory array 530); read level calibration 580 (e.g., to operate a calibration procedure to identify a new read voltage level of a particular portion or portions of the memory array 530); and error detection processing 590 (e.g., to identify and correct errors from data obtained in read operations, to identify one or more RBER(s) for a particular read operation or set of operations, etc.).
In an example, the host operation processing 555 is used to interpret and process the host IO commands 525 (e.g., read and write commands) and initiate accompanying commands in the controller 540 and the memory array 530 to accomplish the host IO commands 525. Further, in response to the host IO commands 525, and the IO operation monitoring 550, and error detection processing 590, the host operation processing 555 may coordinate timing, conditions, and parameters of the read scan control 560.
In an example, the IO operation monitoring 550 operates to track reads and writes to the memory array initiated by host IO commands. The IO operation monitoring 550 also operates to track accompanying IO operations and states, such as a host IO active or inactive state (e.g., where an active state corresponds to the state of the controller 540 and memory array 530 actively performing read or write IO operations initiated from the host 520, and where an inactive state corresponds to an absence of performing such IO operations initiated from the host 520). The IO operation monitoring 550 may also monitor aspects of voltage level and read error rates occurring with the IO operations initiated from the host 520, in connection with determining parameters for read scan control 560 as discussed herein.
In an example, the read scan control 560 operates to identify parameters in the memory array 530 and controller 540 for scheduling and conducting a read scan operation 585, such as based on the IO conditions (e.g., indicated by the IO operation monitoring 550) or error conditions (e.g., indicated by the error detection processing 590). The read scan control 560 further defines one or more scheduled conditions and one or more trigger windows for scheduling the read scan operation 585 and preemptively launching the read scan operation 585 during the trigger window(s). The read scan control 560 further operates to initiate and perform the read scan operation 585 based on these or other parameters, through synchronous or asynchronous event processing as illustrated and discussed below with reference to FIGS. 6A and 6B.
In an example, the read voltage control 570 is used to establish, change, and provide a voltage value used to read a particular area of memory (such as a respective block in the memory array 530). For example, the read voltage control 570 may implement various positive or negative offsets in order to read respective memory cells and memory locations (e.g., pages, blocks, dies) including the respective memory cells.
In an example, the read level calibration 580 is used to establish (e.g., change, update, reset, etc.) the value of the read voltage implemented by the read voltage control 570. The read level calibration 580 may be implemented through multiple sampling commands performed on the memory array 530, such as sampling commands issued at varying voltages to multiple areas of the memory array, which attempt to determine a read voltage that is optimized to the Vt of those areas. The read level calibration 580 may operate in connection with the features of the host operation processing 555, the read scan control 560, or the error detection processing 590. For instance, the host operation processing 555 may identify memory locations for sampling based on IO read operations to those locations; also for instance, the read scan control 560 may trigger performance of the read level calibration 580 in response to an increasing RBER trend of various read scans; also for instance, the error detection processing 590 may trigger the read level calibration 580 in response to particular conditions of errors or an error rate of read data (e.g., in data read from a block) as exceeding a particular threshold.
In an example, the error detection processing 590 may detect a recoverable error condition (e.g., a RBER value or an RBER trend), an unrecoverable error condition, or other measurements or error conditions for a memory cell, a group of cells, or larger areas of the memory array (e.g., averages or samples from a block, group of blocks, die, group of dies, etc.). Also in an example, the error detection processing 590 may operate to trigger an event or condition of a read scan via the read scan control 560, or to trigger or schedule a calibration operation with the read level calibration 580.
As discussed herein, the read scan control 560 may involve aspects of scheduling and coordinating a read scan operation 585 to occur at or in response to a scheduled condition (e.g., at a determined time, in response to a particular event or occurrence), identifying a trigger window for preemptive triggering of the read scan operation, and initiating the read scan operation preemptively before the scheduled condition during an idle state in the trigger window. When triggered, the read scan operation may include performing reads of sets of sampled pages or word lines of a plurality of blocks of the memory array 530; the read scan operation also may perform such reads with different read voltages among the plurality of blocks of the memory array 530. In an example, the read scan control 560 operates to select the plurality of blocks at random from within the memory array 530 (e.g., with random sampling); in another example, the read scan control 560 operates to select specific plurality of blocks based on: frequency or recency of access, age of data retention, or an error rate (e.g., RBER) of read operations at a particular location, such as based upon locations of read operations as tracked by the IO operation monitoring 550.
Additionally, the sampling and read operations that are performed in a read scan by the read scan control 560 may allow configuration, such as from a specification (e.g., a determined setting or calculation) of: a size of data (e.g., data corresponding to a page, block, group of blocks, die) that is sampled; a number of pages in total that are sampled; a number of pages within a block that are sampled; whether certain cells, pages, blocks, dies, or certain types of such cells, pages, blocks, dies are or are not sampled; and the like. Likewise, the sampling that is performed in a read scan by the read scan control 560 may be adjusted according to certain benchmarks, user patterns, read access patterns, or other characteristics to match the real-world actual or expected usage of the storage device.
In addition to the techniques discussed herein, other aspects of maintenance operations may be implemented by the control operations 542 in the controller 540. Such operations may include garbage collection or reclamation, wear leveling, block management, and other forms of background activities performed upon the memory array 530. Such background activities may be triggered during an idle state detected by the IO operation monitoring 550, such as immediately following or concurrently with a read scan operation.
FIG. 6A illustrates a timeline scenario 600A of an example read scan trigger criteria implementing time-based condition triggers for preemptive idle time read scan operations in a memory device. Specifically, the timeline scenario 600A illustrates an event timeline 620A occurring from t0 to t as contrasted with an IO operation timeline 610 illustrating read and write operations occurring from host IO.
As shown, event timeline 620 includes various scheduled triggers for a read scan operation based on synchronous activity, including scheduled condition X (to occur at time X) and scheduled condition Y (to occur at time Y). For instance, a read scan operation may be scheduled at a regular interval to occur every Y-X minutes (e.g., every n seconds, minutes, hours, days, etc.). In the depiction of the timeline scenario 600A, the event timeline 620A may operate to ensure that a respective read scan operation is commenced at no later than scheduled time X and scheduled time Y, meaning that the respective read scan operation can begin earlier than time X and time Y within a trigger window.
The IO operation timeline 610, in contrast, includes bursts of host IO activity that is unlikely to occur according to a defined schedule. As shown, the IO operation timeline 610 includes a number of IO operations (designated by respective “X” characters), in addition to periods of time in which the IO operations are not being conducted (designated by white space). The periods of time in which the IO operations are not being conducted include periods 640A, 640B, 640C, indicating an idle state for host IO operations. It will be understood that the periods 640A, 640B, 640C and the timelines 610, 620A are provided with a simplified representation for illustrative purposes, as other memory device operations are not illustrated in the timeline scenario 600A for purposes of simplicity.
The event timeline 620A further depicts respective preemptive trigger windows 630A, 630B, which are used to designate a preemptive period of time to perform read scan operations. Specifically, the trigger window 630A starts at time X-t and continues until time X; the trigger window 630B starts at time Y-t and continues until time Y. The memory device may monitor for a respective idle state of host IO operations, with the idle state used to initiate and conduct read scan operations within the idle states occurring within the trigger windows 630A, 630B.
The timeline scenario 600A provides an implementation of preemptive synchronized read scans that are pre-scheduled based on a time interval or other times. For example, when synchronized read scans are utilized, an absolute trigger limit for a read scan may be set to every N time-units (e.g., seconds, minutes, hours, or days), and the window-based criterion for the lower trigger limit is N-t time units, where t can be a configurable parameter. In this scenario, a preemptive read scan may be triggered in the background every N-t time-units, if the host IO is idle; else, the preemptive read scan is triggered at N time-units in the foreground. In contrast, with an absolute trigger-based approach, the read scan is triggered only at X (even when the host IO is active).
As a first example, within trigger window 630A (starting at time X-t), the host IO activity continues until the first idle period 640A. In response to the host IO becoming idle and the memory device entering a corresponding idle state, a preemptive read scan operation may commence. Specifically, the read scan operation, which was otherwise scheduled to occur at time X (the originally scheduled condition), will now begin during the first idle period 640A. In the event that the preemptive read scan operation cannot complete in the background within the first idle period 640A because host IO activity occurs, the preemptive read scan operation may be delayed or may continue. In an example, the preemptive read scan operation may pause until resuming at time X. In another example, the preemptive read scan operation may continue at a lower priority than host IO operations when the host IO activity resumes, but then become prioritized at time X to ensure that the read scan completes.
As a second example, within trigger window 630B (starting at time Y-t), the host IO activity continues until the second idle period 640B. In response to the host IO becoming idle and the memory device entering a corresponding idle state, another preemptive read scan operation may commence. Specifically, this read scan operation, which was otherwise scheduled to occur at time Y, will now begin during the second idle period 640B. Similar to the example above, the event that the preemptive read scan operation cannot complete within the second idle period 640B (e.g., because host IO activity occurs), the preemptive read scan operation may be delayed or may continue. In a further example, when interrupted by host IO activity, the preemptive read scan operation may be delayed until another host idle time occurs (e.g., at the third idle period 640C); in another example, the preemptive read scan operation may be delayed no longer than time Y.
FIG. 6B illustrates a timeline scenario 600B of an example read scan trigger criteria implementing event-based condition triggers for preemptive idle time read scan operations in a memory device. In a similar fashion to timeline scenario 600A, the timeline scenario 600B illustrates an event timeline 620B occurring from t0 to t as contrasted with an IO operation timeline 610 illustrating read and write operations occurring from host IO. However, the event timeline 620B includes scheduled conditions that result from event or occurrence triggers (e.g., asynchronous activity) rather than from predetermined times.
As shown, event timeline 620B includes various scheduled triggers for a read scan operation based on asynchronous activity, including scheduled condition X (e.g., to occur as a result of a particular event or occurrence) and scheduled condition Y (to occur as a result of a particular event or occurrence). For instance, a read scan operation may be scheduled to occur when a frequency of errors (e.g., error handling trigger events in a block) exceeds a certain rate or amount, when an event count exceeds a determined threshold, or when a particular attribute (e.g., of the memory array, the memory controller, or one or more modules in a firmware of the memory controller) is detected. In the operation of the timeline scenario 600B, the event timeline 620B may operate to ensure that a respective read scan operation is commenced at no later than scheduled condition X and scheduled condition Y, meaning, the read scan operation can be commenced earlier than scheduled event X and scheduled event Y within a trigger window.
Again in contrast, the IO operation timeline 610, includes bursts of host IO activity that is unlikely to occur according to a defined schedule. As shown, the IO operation timeline 610 includes a number of IO operations, and periods of time in which the IO operations are not being conducted (periods 640A, 640B, 640C). The event timeline 620B further depicts the asynchronous nature of the events, and the varying sizes of the trigger windows 650A, 650B, which are used to designate a preemptive period of time to perform read scan operations. Specifically, the trigger window 650A starts at the occurrence of event X′ and continues to the occurrence of event X; the trigger window 650B starts at the occurrence of event Y′ and continues to the occurrence of event Y. Notably, the trigger window 650A is smaller than the trigger window 650B, due to the asynchronous nature of the events occurring in the memory device and the host IO. However, the memory device may continue to monitor for a respective idle state that is used to perform read scan operations within the trigger windows 650A, 650B.
The timeline scenario 600B provides an implementation of preemptive asynchronous read scans used to address read disturb, such as where a trigger event is based on a block read count threshold. For example, a window-based read count threshold criterion can be set for the trigger window, such that once a lower limit (event X′) for the threshold is met, the storage device can schedule the read scan to pre-emptively occur when the host IO encounters an idle event (before event X). Additionally, in a further example, the window trigger criterion can be modulated in response to certain event triggers such as an extent of error handling (e.g., a number of steps in an error handling flow). Based on the number of steps in the error handling flow required to recover errors or the error handling trigger rate, the system can modulate time-based or block usage-based read scan criteria to adapt to the changing media characteristics.
As a first example, within trigger window 650A (starting at the occurrence of event X′), the host IO activity continues until the first idle period 640A. In response to the host IO becoming idle and the memory device entering a corresponding idle state, the preemptive read scan operation may commence. Specifically, the read scan operation, which was otherwise scheduled to occur at (or after) the occurrence of event X, will now begin during the first idle period 640A. In the event that the read scan operation cannot complete in the background within the first idle period 640A because host IO activity occurs, the read scan operation may be delayed or may continue (e.g., as discussed above with reference to timeline scenario 600A).
As a second example, within trigger window 650B (starting at the occurrence of event Y′), the host IO activity continues until the second idle period 640B. In response to the host IO becoming idle and the memory device entering a corresponding idle state, another preemptive read scan operation may commence. Specifically, this read scan operation, which was otherwise scheduled to occur at or after the occurrence of event Y, will now begin during the second idle period 640B. Notably, the trigger window 650B is indicated as being a different size than trigger window 650A, due to the asynchronous nature of the events. Thus, as shown, an additional host idle period (third idle period 640C) may occur within the trigger window 650B. The third idle period 640C may be used to launch additional background operations, to complete read scan operations, or to perform additional scheduled and coordinated idle time tasks.
In contrast to the techniques illustrated in FIGS. 6A and 6B, conventional approaches typically utilize a single, absolute criterion for time, frequency, or other metrics to trigger a read scan operation. Thus, conventional approaches are not optimized to perform read scans during the background host idle time and may result in higher collision rate with host IO. In particular, read scan triggers often occur in the foreground, which causes a storage device to multiplex read scan operations along with the host IO traffic, thus impacting performance of both types of operations. Collisions also result in an increased latency to service the host IO commands. These concerns are addressed with the approaches discussed herein, which provide flexibility and optimization to preemptively schedule and launch read scans, and as applicable, delay and coordinate such read scans.
FIG. 7 illustrates a flowchart 700 of an example set of operations adapted for performing preemptive idle time read scan operations in a memory device. In an example, the operations of the flowchart 700 may be implemented by a controller (e.g., controller 115, 540) of a storage device, through a combination of executed operations in software, firmware, or configured hardware. However, some or all aspects of the following techniques may be implemented by other components (e.g., as initiated by a host) in connection with other commands, controls, and forms of orchestration.
In an example, the operations of the flowchart 700 may be implemented in a memory device, the memory device comprising a NAND memory array having groups of multiple blocks of memory cells, and a memory controller operably coupled to the memory array, with the memory controller adapted (e.g., configured, arranged, programmed) to perform the respective operations. In another example, the operations of the flowchart 700 may be implemented in a method performed by or on a memory controller (or with modules of the memory controller) that controls a NAND memory array, the memory array having groups of multiple blocks of memory cells. In an example, the operations of the flowchart 700 may be implemented in a device readable storage medium, which provides instructions to perform the respective operations when executed (e.g., when executed by a controller of a memory device).
The flowchart 700 is shown as commencing with the identification of conditions in a memory device for scheduling a read scan operation (operation 710). These conditions may include the establishment of a scheduled time condition for a read scan (e.g., such that a read scan must be performed or attempted every n intervals of time), the establishment of a scheduled frequency or evaluative condition (e.g., such that a read scan must be performed in response to n reads occurring, or in response to an error rate exceeding m), or the establishment of an event-based condition (e.g., such that a read scan must be performed in response to certain detected conditions such as events or attributes within the memory device).
The definition of the read scan scheduling is accompanied by the definition of a trigger window for a preemptive read scan operation (operation 720). For example, the definition of a trigger window may be based on a variation of the scheduled event, conditions in the memory device, or a time-based window, which precedes the scheduled condition. In connection with the definition of the trigger window, a read scan operation is scheduled to occur upon occurrence of the scheduled condition (operation 730), which is coordinated with the end of the defined trigger window. The scheduled condition may be time, frequency, or event based, as discussed in the asynchronous and synchronous examples herein.
As discussed herein, the read scan operation may be defined to sample data at multiple locations of the memory array by performing reads at the multiple locations. In further examples, the read scan operation may include tracking of error rates, error rate trends, and other conditions based on the results of the read scans among the multiple locations. For instance, the read scan operation may include performing reads of sets of sampled pages or word lines of a plurality of blocks of the memory array, such that the reads are performed with different read voltages among the plurality of blocks. In still further examples, the plurality of blocks are selected at random from within the NAND memory array.
The flowchart 700 continues with the monitoring of the operational state of host IO operations with the memory device (operation 740). In an example, this may include monitoring the operational state of the memory device to identify an active state corresponding to the performance of operations initiated from a host, or an idle state corresponding to an absence of operations initiated from the host. Based on this monitoring, an idle state of the host IO operations may be identified and detected within the defined trigger window, prior to the scheduled condition (operation 750).
In response to the operational state of the memory device entering the idle state during the trigger window, the read scan operation may be preemptively initiated (operation 760). Thus, during the idle state of host IO operations within the trigger window, the read scan operation may preemptively occur before the scheduled condition.
The flowchart 700 continues with an optional condition to pause a read scan operation that is not complete (operation 770). The pausing of a read scan operation may occur within a trigger window, prior to the scheduled condition, such as when the idle state transitions into an active state of host IO operations. With this optional condition, the flowchart 700 resumes to await an identification of the idle state of host IO operations (operation 750), and initiate the read scan operation upon the occurrence of the idle state within the trigger window (operation 760).
The flowchart 700 concludes with the completion of the read scan operation, and the performance of any additional operation(s) such as read voltage calibration based on the read scans (operation 780). If the read scan operations have not completed during the idle state(s) by the scheduled event (e.g., as paused by operation 770), the read scan operations may be completed upon occurrence of the scheduled condition.
Finally, in an optional example, where the memory device remains in an idle state, additional maintenance tasks such as garbage collection or reclamation, wear leveling, block retirement, and the like may be initiated on the memory device (operation 790). Specifically, pre-emptive read scans may be one of several background tasks performed by the memory device during the host idle state. In a further example, a background module of the memory device governs the priority and scheduling aspects of the maintenance tasks. For instance, read scans may be pre-emptively triggered during host idle time based on the trigger window, but will not necessarily take a higher priority over other background tasks managed by the background module. Accordingly, coordination and scheduling may be performed by the background module to allow the maintenance tasks to be conducted before, after, concurrently, or in compliment with the read scan operations.
In response to the operational state of the memory array not entering the idle state during the trigger window, the read scan operation may be initiated to occur no later than the scheduled event. For instance, consider a scenario where a second read scan operation is scheduled to be conducted upon occurrence of a second scheduled condition. The second read scan may be initiated in response to the operational state of the memory not entering the idle state before the second scheduled condition, such that the second read scan operation is initiated to occur in response to the second scheduled condition (e.g., without preemptive scheduling). Thus, if preemptive scheduling is unsuccessful or cannot be utilized as a background operation within a trigger window, the read scan operation may still be initiated within the foreground.
It will be understood that these and the other example implementations discussed above are provided as examples, and may be accompanied by other time and operational optimizations to maximize efficiency and use of idle time. Further, the techniques for sampling and triggering the voltage calibration may modified to be integrated with use of existing read scan triggers, conditions, and operations, providing a minimal or even zero impact as compared with conventional read scan triggering techniques.
FIG. 8 illustrates a block diagram of an example machine 800 upon which any one or more of the techniques (e.g., methodologies) discussed herein may perform. In alternative embodiments, the machine 800 may operate as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine 800 may operate in the capacity of a server machine, a client machine, or both in server-client network environments. In an example, the machine 800 may act as a peer machine in peer-to-peer (P2P) (or other distributed) network environment. The machine 800 may be a personal computer (PC), a tablet PC, a set-top box (STB), a personal digital assistant (PDA), a mobile telephone, a web appliance, an IoT device, automotive system, or any machine capable of executing instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.
The machine (e.g., computer system) 800 (e.g., the host device 105, the memory device 110, etc.) may include a hardware processor 802 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof, such as the memory controller 115, etc.), a main memory 804 and a static memory 806, some or all of which may communicate with each other via an interlink (e.g., bus) 808. The machine 800 may further include a display unit 810, an alphanumeric input device 812 (e.g., a keyboard), and a user interface (UI) navigation device 814 (e.g., a mouse). In an example, the display unit 810, input device 812 and UI navigation device 814 may be a touch screen display. The machine 800 may additionally include a storage device (e.g., drive unit) 816, a signal generation device 818 (e.g., a speaker), a network interface device 820, and one or more sensors 816, such as a global positioning system (GPS) sensor, compass, accelerometer, or other sensor. The machine 800 may include an output controller 828, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).
The storage device 816 may include a machine readable medium 822 on which is stored one or more sets of data structures or instructions 824 (e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions 824 may also reside, completely or at least partially, within the main memory 804, within static memory 806, or within the hardware processor 802 during execution thereof by the machine 800. In an example, one or any combination of the hardware processor 802, the main memory 804, the static memory 806, or the storage device 816 may constitute the machine readable medium 822.
While the machine readable medium 822 is illustrated as a single medium, the term “machine readable medium” may include a single medium or multiple media (e.g., a centralized or distributed database, or associated caches and servers) configured to store the one or more instructions 824.
The term “machine readable medium” may include any medium that is capable of storing, encoding, or carrying instructions for execution by the machine 800 and that cause the machine 800 to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting machine readable medium examples may include solid-state memories, and optical and magnetic media. In an example, a massed machine readable medium comprises a machine-readable medium with a plurality of particles having invariant (e.g., rest) mass. Accordingly, massed machine-readable media are not transitory propagating signals. Specific examples of massed machine readable media may include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.
The instructions 824 (e.g., software, programs, an operating system (OS), etc.) or other data are stored on the storage device 821, can be accessed by the memory 804 for use by the processor 802. The memory 804 (e.g., DRAM) is typically fast, but volatile, and thus a different type of storage than the storage device 821 (e.g., an SSD), which is suitable for long-term storage, including while in an “off” condition. The instructions 824 or data in use by a user or the machine 800 are typically loaded in the memory 804 for use by the processor 802. When the memory 804 is full, virtual space from the storage device 821 can be allocated to supplement the memory 804; however, because the storage 821 device is typically slower than the memory 804, and write speeds are typically at least twice as slow as read speeds, use of virtual memory can greatly reduce user experience due to storage device latency (in contrast to the memory 804, e.g., DRAM). Further, use of the storage device 821 for virtual memory can greatly reduce the usable lifespan of the storage device 821.
In contrast to virtual memory, virtual memory compression (e.g., the Linux® kernel feature “ZRAM”) uses part of the memory as compressed block storage to avoid paging to the storage device 821. Paging takes place in the compressed block until it is necessary to write such data to the storage device 821. Virtual memory compression increases the usable size of memory 804, while reducing wear on the storage device 821.
The instructions 824 may further be transmitted or received over a communications network 826 using a transmission medium via the network interface device 820 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks may include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone (POTS) networks, and wireless data networks (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards known as Wi-Fi®, IEEE 802.16 family of standards known as WiMax™), IEEE 802.15.4 family of standards, peer-to-peer (P2P) networks, among others. In an example, the network interface device 820 may include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to the communications network 826. In an example, the network interface device 820 may include a plurality of antennas to wirelessly communicate using at least one of single-input multiple-output (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. The term “transmission medium” shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the machine 800, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.
The term “horizontal” as used in this document is defined as a plane parallel to the conventional plane or surface of a substrate, such as that underlying a wafer or die, regardless of the actual orientation of the substrate at any point in time. The term “vertical” refers to a direction perpendicular to the horizontal as defined above. Prepositions, such as “on,” “over,” and “under” are defined with respect to the conventional plane or surface being on the top or exposed surface of the substrate, regardless of the orientation of the substrate; and while “on” is intended to suggest a direct contact of one structure relative to another structure which it lies “on” (in the absence of an express indication to the contrary); the terms “over” and “under” are expressly intended to identify a relative placement of structures (or layers, features, etc.), which expressly includes—but is not limited to—direct contact between the identified structures unless specifically identified as such. Similarly, the terms “over” and “under” are not limited to horizontal orientations, as a structure may be “over” a referenced structure if it is, at some point in time, an outermost portion of the construction under discussion, even if such structure extends vertically relative to the referenced structure, rather than in a horizontal orientation.
The terms “wafer” and “substrate” are used herein to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the various embodiments is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
Additional examples of the presently described embodiments are suggested according to the structures and techniques described above and specified in the following examples and claims.
Example 1 is a memory device, comprising: a NAND memory array; and a memory controller operably coupled to the memory array, the memory controller to perform operations comprising: scheduling a read scan operation on the memory array to occur upon a scheduled condition, wherein the read scan operation is to sample data at multiple locations of the memory array by performing reads at the multiple locations; monitoring an operational state of the memory array, the operational state of the memory array including an active state corresponding to performing operations initiated from a host, and an idle state corresponding to an absence of operations initiated from the host; and initiating the read scan operation in response to the operational state of the memory array entering the idle state, wherein the read scan operation is initiated to preemptively occur before the scheduled condition.
In Example 2, the subject matter of Example 1 includes, the read scan operation performing reads of sets of sampled pages or word lines of a plurality of blocks of the memory array, wherein the reads are performed with different read voltages among the plurality of blocks.
In Example 3, the subject matter of Example 2 includes, the plurality of blocks being selected at random from within the NAND memory array.
In Example 4, the subject matter of Examples 1-3 includes, scheduling a second read scan operation on the memory array to be conducted upon a second scheduled condition; and initiating the second read scan operation in response to the operational state of the memory array not entering an idle state before the second scheduled condition, wherein the second read scan operation is initiated to occur upon the second scheduled condition.
In Example 5, the subject matter of Examples 1-4 includes, the scheduled condition being a time determined from a scheduled time interval, wherein the initiating of the read scan operation preemptively occurs upon entering the idle state during a predetermined time period prior to the scheduled condition.
In Example 6, the subject matter of Examples 1-5 includes, the scheduled condition being a frequency-based condition, wherein the scheduling of the read scan operation is performed in response to a frequency of error handling trigger events in a block exceeding a determined threshold.
In Example 7, the subject matter of Examples 1-6 includes, the scheduled condition being a predetermined event, wherein the scheduling of the read scan operation is performed in response to the predetermined event occurring within the memory controller, or in response to the predetermined event being identified from an attribute of: the memory array, the memory controller, or one or more modules in a firmware of the memory controller.
In Example 8, the subject matter of Example 7 includes, the predetermined event that occurs within the memory controller corresponding to a block read count exceeding a determined block read count threshold.
In Example 9, the subject matter of Examples 1-8 includes, initiating a wear leveling operation in response to the operational state of the memory array entering the idle state, wherein the wear leveling operation is initiated to occur after completion of the read scan operation.
In Example 10, the subject matter of Examples 1-9 includes, in response to initiating the read scan operation to preemptively occur before the scheduled condition: stopping the read scan operation in response to the operational state of the memory array entering the active state before the scheduled condition; and, in response to re-entering the idle state or in response to occurrence of the scheduled condition, resuming the read scan operation.
In Example 11, the subject matter of Examples 1-10 includes, the operations initiated from the host including read operations or write operations, with the operations further comprising: prioritizing the read scan operation over operations initiated from the host, in response to occurrence of the scheduled condition before a preemptive completion of the read scan operation.
In Example 12, the subject matter of Examples 1-11 includes, initiating read voltage calibration of at least a portion of the memory array in response to data obtained from the reads conducted among the multiple locations of the memory array with the read scan operation.
In Example 13, the subject matter of Example 12 includes, the read scan operation performing sampling of a raw bit error rate (RBER) from the multiple locations in the memory array using multiple read voltages among the multiple locations, wherein the read voltage calibration is performed in response to the RBER exceeding a predetermined threshold.
In Example 14, the subject matter of Examples 1-13 includes, the memory array including at least one of: single-level cell (SLC), multi-layer cell (MLC), triple-layer cell (TLC), or quad-layer cell (QLC) NAND memory cells.
In Example 15, the subject matter of Examples 1-14 includes, the memory array being arranged into a stack of three-dimensional (3D) NAND dies.
Example 16 is a method for performing preemptive read scans in a memory device, the method comprising a plurality of operations performed by a memory controller upon a NAND memory array of the memory device, with the operations comprising: scheduling a read scan operation on the memory array to be conducted upon a scheduled condition, wherein the read scan operation is to sample data at multiple locations of the memory array by performing reads at the multiple locations, and wherein the reads are performed with different read voltages among the multiple locations; monitoring an operational state of the memory array, the operational state of the memory array including an active state corresponding to performing operations initiated from a host, and an idle state corresponding to an absence of operations initiated from the host; and initiating the read scan operation in response to the operational state of the memory array entering the idle state, wherein the read scan operation is initiated to preemptively occur before the scheduled condition.
In Example 17, the subject matter of Example 16 includes, the read scan operation performing reads of sets of sampled pages or word lines of a plurality of blocks of the memory array, wherein the reads are performed with different read voltages among the plurality of blocks.
In Example 18, the subject matter of Example 17 includes, the plurality of blocks being selected at random from within the NAND memory array.
In Example 19, the subject matter of Examples 16-18 includes: scheduling a second read scan operation on the memory array to be conducted upon a second scheduled condition; and initiating the second read scan operation in response to the operational state of the memory array not entering an idle state before the second scheduled condition, wherein the second read scan operation is initiated to occur upon the second scheduled condition.
In Example 20, the subject matter of Examples 16-19 includes, the scheduled condition being a time determined from a scheduled time interval, wherein the initiating of the read scan operation preemptively occurs upon entering the idle state during a predetermined time period prior to the scheduled condition.
In Example 21, the subject matter of Examples 16-20 includes, the scheduled condition being a frequency-based condition, wherein the scheduling of the read scan operation is performed in response to a frequency of error handling trigger events in a block exceeding a determined threshold.
In Example 22, the subject matter of Examples 16-21 includes, the scheduled condition being a predetermined event, wherein the scheduling of the read scan operation is performed in response to the predetermined event occurring within the memory controller, or in response to the predetermined event being identified from an attribute of: the memory array, the memory controller, or one or more modules in a firmware of the memory controller.
In Example 23, the subject matter of Example 22 includes, the predetermined event occurring within the memory controller corresponding to a block read count exceeding a determined block read count threshold.
In Example 24, the subject matter of Examples 16-23 includes: initiating a wear leveling operation in response to the operational state of the memory array entering the idle state, wherein the wear leveling operation is initiated to occur after completion of the read scan operation.
In Example 25, the subject matter of Examples 16-24 includes, in response to initiating the read scan operation to preemptively occur before the scheduled condition, stopping the read scan operation in response to the operational state of the memory array entering the active state before the scheduled condition; and in response to re-entering the idle state or in response to occurrence of the scheduled condition, resuming the read scan operation.
In Example 26, the subject matter of Examples 16-25 includes, the operations initiated from the host including read operations or write operations, with the operations further comprising: prioritizing the read scan operation over operations initiated from the host, in response to occurrence of the scheduled condition before a preemptive completion of the read scan operation.
In Example 27, the subject matter of Examples 16-26 includes, initiating read voltage calibration of at least a portion of the memory array, in response to data obtained from the reads conducted among the multiple locations of the memory array with the read scan operation.
In Example 28, the subject matter of Example 27 includes, the read scan operation performing sampling of a raw bit error rate (RBER) from the multiple locations in the memory array using multiple read voltages among the multiple locations, wherein the read voltage calibration is performed in response to the RBER exceeding a predetermined threshold.
In Example 29, the subject matter of Examples 16-28 includes, wherein the memory array includes at least one of: single-level cell (SLC), multi-layer cell (MLC), triple-layer cell (TLC), or quad-layer cell (QLC) NAND memory cells.
In Example 30, the subject matter of Examples 16-29 includes, wherein the memory array is arranged into a stack of three-dimensional (3D) NAND dies.
Example 31 is a device readable storage medium, that provides instructions that, when executed by a controller of a memory device, performs preemptive read scans on a NAND memory array of the memory device, wherein the instructions cause the controller to perform operations according to any of the techniques of Examples 1-30.
Example 32 is an apparatus comprising respective means for performing any of the methods or techniques of Examples 1-30.
Example 33 is a system, apparatus, or device to perform the operations of any of Examples 1-30.
Example 34 is a tangible machine readable medium embodying instructions to perform or implement the operations of any of Examples 1-30.
Example 35 is a method to perform the operations of any of Examples 1-30.
a NAND memory array; and
a memory controller operably coupled to the memory array, the memory controller to perform operations comprising: scheduling a read scan operation on the memory array to occur upon a scheduled condition, wherein the read scan operation is to sample data at multiple locations of the memory array by performing reads at the multiple locations; monitoring an operational state of the memory array, the operational state of the memory array including an active state corresponding to performing operations initiated from a host, and an idle state corresponding to an absence of operations initiated from the host; and initiating the read scan operation in response to the operational state of the memory array entering the idle state, wherein the read scan operation is initiated to preemptively occur before the scheduled condition.
2. The memory device of claim 1, wherein the read scan operation includes performing reads of sets of sampled pages or word lines of a plurality of blocks of the memory array, and wherein the reads are performed with different read voltages among the plurality of blocks.
3. The memory device of claim 2, wherein the plurality of blocks are selected at random from within the NAND memory array.
4. The memory device of claim 1, the operations further comprising:
scheduling a second read scan operation on the memory array to be conducted upon a second scheduled condition; and
initiating the second read scan operation in response to the operational state of the memory array not entering an idle state before the second scheduled condition, wherein the second read scan operation is initiated to occur upon the second scheduled condition.
5. The memory device of claim 1, wherein the scheduled condition is a time determined from a scheduled time interval, and wherein the initiating of the read scan operation preemptively occurs upon entering the idle state during a predetermined time period prior to the scheduled condition.
6. The memory device of claim 1, wherein the scheduled condition is a frequency-based condition, and wherein the scheduling of the read scan operation is performed in response to a frequency of error handling trigger events in a block exceeding a determined threshold.
7. The memory device of claim 1, wherein the scheduled condition is a predetermined event, and wherein the scheduling of the read scan operation is performed in response to the predetermined event occurring within the memory controller, or in response to the predetermined event being identified from an attribute of: the memory array, the memory controller, or one or more modules in a firmware of the memory controller.
8. The memory device of claim 7, wherein the predetermined event occurring within the memory controller corresponds to a block read count exceeding a determined block read count threshold.
9. The memory device of claim 1, the operations further comprising:
initiating a wear leveling operation in response to the operational state of the memory array entering the idle state, wherein the wear leveling operation is initiated to occur after completion of the read scan operation.
10. The memory device of claim 1, wherein in response to initiating the read scan operation to preemptively occur before the scheduled condition, the operations further comprise:
stopping the read scan operation in response to the operational state of the memory array entering the active state before the scheduled condition; and
resuming the read scan operation, in response to re-entering the idle state or in response to occurrence of the scheduled condition.
11. The memory device of claim 1, wherein the operations initiated from the host include read operations or write operations, with the operations further comprising:
prioritizing the read scan operation over operations initiated from the host, in response to occurrence of the scheduled condition before a preemptive completion of the read scan operation.
12. The memory device of claim 1, the operations further comprising:
initiating read voltage calibration of at least a portion of the memory array in response to data obtained from the reads conducted among the multiple locations of the memory array with the read scan operation.
13. The memory device of claim 12, wherein the read scan operation performs sampling of a raw bit error rate (RBER) from the multiple locations in the memory array using multiple read voltages among the multiple locations, and wherein the read voltage calibration is performed in response to the RBER exceeding a predetermined threshold.
14. The memory device of claim 1, wherein the memory array includes at least one of: single-level cell (SLC), multi-layer cell (MLC), triple-layer cell (TLC), or quad-layer cell (QLC) NAND memory cells.
15. The memory device of claim 1, wherein the memory array is arranged into a stack of three-dimensional (3D) NAND dies.
16. A method for performing preemptive read scans in a memory device, the method comprising a plurality of operations performed by a memory controller upon a NAND memory array of the memory device, with the operations comprising:
scheduling a read scan operation on the memory array to be conducted upon a scheduled condition, wherein the read scan operation is to sample data at multiple locations of the memory array by performing reads at the multiple locations, and wherein the reads are performed with different read voltages among the multiple locations;
monitoring an operational state of the memory array, the operational state of the memory array including an active state corresponding to performing operations initiated from a host, and an idle state corresponding to an absence of operations initiated from the host; and
initiating the read scan operation in response to the operational state of the memory array entering the idle state, wherein the read scan operation is initiated to preemptively occur before the scheduled condition.
17. The method of claim 16, wherein the read scan operation includes performing reads of sets of sampled pages or word lines of a plurality of blocks of the memory array, and wherein the plurality of blocks are selected at random from within the NAND memory array.
18. The method of claim 16, wherein the scheduled condition is a time determined from a scheduled time interval, and wherein the initiating of the read scan operation preemptively occurs upon entering the idle state during a predetermined time period prior to the scheduled condition.
19. The method of claim 16, wherein the scheduling of the read scan operation is performed in response to: a frequency of error handling trigger events in a block exceeding a determined threshold, an event occurring within the memory controller, or an event being identified from an attribute of: the memory array, the memory controller, or one or more modules in a firmware of the memory controller.
20. The method of claim 16, wherein in response to initiating the read scan operation to preemptively occur before the scheduled condition, the operations further comprise:
21. The method of claim 16, wherein the operations initiated from the host include read operations or write operations, with the operations further comprising:
22. The method of claim 16, the operations further comprising:
23. The method of claim 22, wherein the read scan operation performs sampling of a raw bit error rate (RBER) from the multiple locations in the memory array using multiple read voltages among the multiple locations, and wherein the read voltage calibration is performed in response to the RBER exceeding a predetermined threshold.
24. A device readable storage medium, that provides instructions that, when executed by a memory controller of a memory device, perform preemptive read scans on a NAND memory array of the memory device, wherein the instructions cause the controller to perform operations comprising:
scheduling a read scan operation on the memory array to be conducted at a scheduled condition, wherein the read scan operation is to sample data at multiple locations of the memory array by performing reads at the multiple locations, and wherein the reads are performed with different read voltages among the multiple locations;
25. The device readable storage medium of claim 24, wherein the read scan operation includes performing reads of sets of sampled pages or word lines of a plurality of blocks of the memory array, and wherein the plurality of blocks are selected at random from within the memory array.
26. The device readable storage medium of claim 24, wherein the scheduled condition is a time determined from a scheduled time interval, and wherein the initiating of the read scan operation preemptively occurs upon entering the idle state during a predetermined time period prior to the scheduled condition.
27. The device readable storage medium of claim 24, wherein the scheduling of the read scan operation is performed in response to: a frequency of error handling trigger events in a block exceeding a determined threshold, an event occurring within the memory controller, or an event being identified from an attribute of: the memory array, the memory controller, or one or more modules in a firmware of the memory controller.
28. The device readable storage medium of claim 24, wherein in response to initiating the read scan operation to preemptively occur before the scheduled condition, the operations further comprise:
29. The device readable storage medium of claim 24, wherein the operations initiated from the host include read operations or write operations, with the operations further comprising:
30. The device readable storage medium of claim 29, the operations further comprising:
31. The device readable storage medium of claim 30, wherein the read scan operation performs sampling of a raw bit error rate (RBER) from the multiple locations in the memory array using multiple read voltages among the multiple locations, and wherein the read voltage calibration is performed in response to the RBER exceeding a predetermined threshold.
8700840 April 15, 2014 Paley et al.
20060233010 October 19, 2006 Li
20080104387 May 1, 2008 Owhadi
20090327581 December 31, 2009 Coulson
20100115345 May 6, 2010 Childs
20120163097 June 28, 2012 Ishikawa et al.
20130055046 February 28, 2013 Blodgett
20140075105 March 13, 2014 Colgrove et al.
20140347923 November 27, 2014 Ghaly
20150006983 January 1, 2015 Lin
20150117107 April 30, 2015 Sun et al.
20150127883 May 7, 2015 Chen et al.
20150262714 September 17, 2015 Tuers et al.
20160117216 April 28, 2016 Muchherla et al.
101699413 April 2010 CN
“International Application Serial No. PCT/CN2017/104945, International Search Report dated Jun. 27, 2018”, 4 pgs.
“International Application Serial No. PCT/CN2017/104945, Written Opinion dated Jun. 27, 2018”, 4 pgs.
Patent Publication Number: 20190103164
Inventors: Ashutosh Malshe (Fremont, CA), Harish Singidi (Fremont, CA), Kishore Kumar Muchherla (Fremont, CA), Michael G. Miller (Boise, ID), Sampath Ratnam (Boise, ID), John Zhang (Shanghai), Jie Zhou (Shanghai)
Application Number: 15/571,232
International Classification: G06F 12/00 (20060101); G11C 16/26 (20060101); G06F 12/02 (20060101); G06F 11/07 (20060101); G11C 7/06 (20060101); G11C 16/34 (20060101); G06F 11/22 (20060101);