Method for the implementation of a high performance, high resiliency and high availability dual controller storage system

A computer-implemented method, according to one embodiment, includes: splitting received information between two controllers of a system in a normal operating mode, the received information including data and metadata; storing the metadata in resilient storage in response to a first of the controllers entering a failed state; updating the first controller with information received while the first controller was in the failed state, the first controller being updated in response to the first controller being repaired; and returning the system to the normal operating mode in response to the first controller being updated. Storing the metadata in resilient storage includes: saving snapshots of the metadata in the resilient storage, and saving changes to the metadata which occur between the snapshots. The changes to the metadata are saved in a log structured array. Moreover, the two controllers store the received information in a specified system memory location.

BACKGROUND

The present invention relates to data storage, and more specifically, this invention relates to data storage system for improved dual controller configurations.

Enterprise storage products are typically subjected to an extremely high reliability and data integrity standards. Current industry standards call for a mean time between failures (MTBF) which corresponds to conventional storage products being in uptime between 99.9999% and 99.999% of the time. Another important factor includes how the storage products behave in fatal failure scenarios which the system was not designed to cope with, such as multiple software nodes or concurrent server failures. Conventional enterprise storage products with capacities in the petabyte (PB) range would take days, or even weeks, to recover from back-up following a fatal failure scenario.

Therefore attempts have been made to utilize recovery tools to repair a storage product and avoid recovering from back-ups. However, repairing a storage product using recovery tools is undesirable as well, as doing so typically result in substantial data and metadata loss. Efforts to overcome this loss by continually back-up the data and metadata to persistent storage has severe performance impact on the system, and in most cases is not even a viable option.

Enterprise storage products are also typically expected to provide a customer with a system that is able to achieve high performance, high resiliency and high availability at a low price point relative to the achieved throughput. In order to meet such standards, a dual controller arrangement may be implemented which is able to provide high performance as long as both controllers are functioning. However, when a failure of either one of the controllers occurs, the system is unable to fully maintain its performance by only using the single remaining controller. Accordingly, a common consideration is whether, after the failure of one of the controllers, the system should continue to serve inputs/outputs (I/Os) as the system is performing without redundancy or backup functionality while only one of the controllers is operational.

It follows that conventional products leave the customer with a tough choice of weighing product downtime during recovery with data loss and reduced performance.

SUMMARY

A computer-implemented method, according to one embodiment, includes: splitting received information between two controllers of a system in a normal operating mode, the received information including data and metadata; storing the metadata in resilient storage in response to a first of the controllers entering a failed state; updating the first controller with information received while the first controller was in the failed state, the first controller being updated in response to the first controller being repaired; and returning the system to the normal operating mode in response to the first controller being updated. Storing the metadata in resilient storage includes: saving snapshots of the metadata in the resilient storage, and saving changes to the metadata which occur between the snapshots. The changes to the metadata are saved in a log structured array. Moreover, the two controllers store the received information in a specified system memory location.

A computer program product, according to another embodiment, includes a computer readable storage medium having program instructions embodied therewith. The computer readable storage medium is not a transitory signal per se. Moreover, the program instructions are readable and/or executable by a processor to cause the processor to perform a method which includes: splitting, by the processor, received information between two controllers of a system in a normal operating mode, the received information including data and metadata; storing, by the processor, the metadata in resilient storage in response to a first of the controllers entering a failed state; updating, by the processor, the first controller with information received while the first controller was in the failed state, the first controller being updated in response to the first controller being repaired; and returning, by the processor, the system to the normal operating mode in response to the first controller being updated. Storing the metadata in resilient storage includes: saving, by the processor, snapshots of the metadata in the resilient storage, and saving, by the processor, changes to the metadata which occur between the snapshots. The changes to the metadata are saved in a log structured array. Moreover, the two controllers store the received information in a specified system memory location.

A system, according to yet another embodiment, includes: two controllers; a processor; and logic integrated with the processor, executable by the processor, or integrated with and executable by the processor, the logic being configured to: split, by the processor, received information between the two controllers in a normal operating mode, the received information including data and metadata; store, by the processor, the metadata in resilient storage in response to a first of the controllers entering a failed state; update, by the processor, the first controller with information received while the first controller was in the failed state, the first controller being updated in response to the first controller being repaired; and return, by the processor, the system to the normal operating mode in response to the first controller being updated. Storing the metadata in resilient storage includes: saving, by the processor, snapshots of the metadata in the resilient storage, and saving, by the processor, changes to the metadata which occur between the snapshots. The changes to the metadata are saved in a log structured array. Moreover, the two controllers store the received information in a specified system memory location.

DETAILED DESCRIPTION

The following description discloses several preferred embodiments of systems, methods and computer program products for managing a dual controller storage system. Some of the embodiments described herein are desirably able to achieve a high performance, high resiliency and high availability dual controller storage system at a low price point relative to the achieved throughput, e.g., as will be described in further detail below.

In one general embodiment, a computer-implemented method includes: splitting received information between two controllers of a system in a normal operating mode, the received information including data and metadata; storing the metadata in resilient storage in response to a first of the controllers entering a failed state; updating the first controller with information received while the first controller was in the failed state, the first controller being updated in response to the first controller being repaired; and returning the system to the normal operating mode in response to the first controller being updated. Storing the metadata in resilient storage includes: saving snapshots of the metadata in the resilient storage, and saving changes to the metadata which occur between the snapshots. The changes to the metadata are saved in a log structured array. Moreover, the two controllers store the received information in a specified system memory location.

In another general embodiment, a computer program product includes a computer readable storage medium having program instructions embodied therewith. The computer readable storage medium is not a transitory signal per se. Moreover, the program instructions are readable and/or executable by a processor to cause the processor to perform a method which includes: splitting, by the processor, received information between two controllers of a system in a normal operating mode, the received information including data and metadata; storing, by the processor, the metadata in resilient storage in response to a first of the controllers entering a failed state; updating, by the processor, the first controller with information received while the first controller was in the failed state, the first controller being updated in response to the first controller being repaired; and returning, by the processor, the system to the normal operating mode in response to the first controller being updated. Storing the metadata in resilient storage includes: saving, by the processor, snapshots of the metadata in the resilient storage, and saving, by the processor, changes to the metadata which occur between the snapshots. The changes to the metadata are saved in a log structured array. Moreover, the two controllers store the received information in a specified system memory location.

In yet another general embodiment, a system includes: two controllers; a processor; and logic integrated with the processor, executable by the processor, or integrated with and executable by the processor, the logic being configured to: split, by the processor, received information between the two controllers in a normal operating mode, the received information including data and metadata; store, by the processor, the metadata in resilient storage in response to a first of the controllers entering a failed state; update, by the processor, the first controller with information received while the first controller was in the failed state, the first controller being updated in response to the first controller being repaired; and return, by the processor, the system to the normal operating mode in response to the first controller being updated. Storing the metadata in resilient storage includes: saving, by the processor, snapshots of the metadata in the resilient storage, and saving, by the processor, changes to the metadata which occur between the snapshots. The changes to the metadata are saved in a log structured array. Moreover, the two controllers store the received information in a specified system memory location.

Now referring toFIG. 3, a storage system300is shown according to one embodiment. Note that some of the elements shown inFIG. 3may be implemented as hardware and/or software, according to various embodiments. The storage system300may include a storage system manager312for communicating with a plurality of media and/or drives on at least one higher storage tier302and at least one lower storage tier306. The higher storage tier(s)302preferably may include one or more random access and/or direct access media304, such as hard disks in hard disk drives (HDDs), nonvolatile memory (NVM), solid state memory in solid state drives (SSDs), flash memory, SSD arrays, flash memory arrays, etc., and/or others noted herein or known in the art. The lower storage tier(s)306may preferably include one or more lower performing storage media308, including sequential access media such as magnetic tape in tape drives and/or optical media, slower accessing HDDs, slower accessing SSDs, etc., and/or others noted herein or known in the art. One or more additional storage tiers316may include any combination of storage memory media as desired by a designer of the system300. Also, any of the higher storage tiers302and/or the lower storage tiers306may include some combination of storage devices and/or storage media.

The storage system manager312may communicate with the drives and/or storage media304,308on the higher storage tier(s)302and lower storage tier(s)306through a network310, such as a storage area network (SAN), as shown inFIG. 3, or some other suitable network type. The storage system manager312may also communicate with one or more host systems (not shown) through a host interface314, which may or may not be a part of the storage system manager312. The storage system manager312and/or any other component of the storage system300may be implemented in hardware and/or software, and may make use of a processor (not shown) for executing commands of a type known in the art, such as a central processing unit (CPU), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc. Of course, any arrangement of a storage system may be used, as will be apparent to those of skill in the art upon reading the present description.

According to some embodiments, the storage system (such as300) may include logic configured to receive a request to open a data set, logic configured to determine if the requested data set is stored to a lower storage tier306of a tiered data storage system300in multiple associated portions, logic configured to move each associated portion of the requested data set to a higher storage tier302of the tiered data storage system300, and logic configured to assemble the requested data set on the higher storage tier302of the tiered data storage system300from the associated portions.

As previously mentioned, enterprise storage products are typically expected to provide a customer with a system that is able to achieve high performance, high resiliency and high availability at a low price point relative to the achieved throughput. In order to meet such standards, a dual controller arrangement may be implemented which is able to provide high performance as long as both controllers are functioning. However, when a failure of either one of the controllers occurs, the system is unable to fully maintain its performance by only using the single remaining controller. Accordingly, a common consideration is whether, after the failure of one of the controllers, the system should continue to serve I/Os as the system is performing without redundancy or backup functionality while only one of the controllers is operational.

In response to experiencing a single controller failure, some conventional products perform a total shutdown, thereby undesirably causing availability to suffer, and meeting the industry standards becomes virtually impossible. Other conventional products attempt to operate normally and continue serving I/Os after the first controller fails, but are unable to successfully do so without the assistance of a second controller. Moreover, when the other controller also fails in such conventional products, metadata and write cache is lost, thereby causing user data loss as well as system state instability and/or corruption.

Some conventional products implement three controllers as a minimal configuration of the system, thus being able to maintain a backup for the metadata and data, and only shutting down the system after failure of two of the three controllers. While this scheme is able to meet the desired industry standards of performance, resiliency and availability, it undesirably increases the price point of the product significantly.

In sharp contrast to the foregoing shortcomings experienced by conventional products, various embodiments described herein are able to achieve a high performance, high resiliency and high availability dual controller storage system at a low price point relative to the achieved throughput.

Referring toFIG. 4, a partial representational view of a dual controller storage system400is illustrated in accordance with one embodiment. As an option, the present storage system400may be implemented in conjunction with features from any other embodiment listed herein, such as those described with reference to the other FIGS. However, such storage system400and others presented herein may be used in various applications and/or in permutations which may or may not be specifically described in the illustrative embodiments listed herein. Further, the storage system400presented herein may be used in any desired environment. ThusFIG. 4(and the other FIGS.) may be deemed to include any possible permutation.

As shown, the storage system400includes two controllers404,406which are both coupled to a load balancer402. Although not shown, load balancer402may receive information (e.g., data and/or metadata) from a host and split the received information into two portions, each of the portions being directed to a respective one of the controllers404,406.

Controllers404,406are further coupled to memory modules408having storage media410. According to various approaches, the storage media410may include one or more random access and/or direct access media, such as hard disks in hard disk drives (HDDs), nonvolatile memory (NVM), solid state memory in solid state drives (SSDs), flash memory, SSD arrays, RAM, flash memory arrays, etc., and/or others noted herein or known in the art. Moreover, it should be noted that although each of the storage media410are numbered the same, any one of the storage media410may implement a different type of media, e.g., depending on the desired embodiment.

As information is directed to each of the controllers404,406, the controllers may implement any one or more of the processes (e.g., operations, sub-operations, etc.) described herein to manage and/or store the information in the memory modules408.

While both of the controllers404,406are operational (e.g., healthy), they preferably use each other to backup the metadata and/or data (e.g., in a write cache). As a result, the controllers404,406may be able to provide desirably effective performance, while also ensuring that a single controller failure will not result in data, metadata, or system state loss. Accordingly, the storage system400may be able to achieve a high performance, high resiliency and high availability dual controller storage system at a low price point relative to the achieved throughput, e.g., as will be described in further detail below.

Now referring toFIG. 5A, a flowchart of a computer-implemented method500for managing a dual controller storage system, is shown according to one embodiment. According to different approaches, the system may be a data storage system, an operating system configured to run one or more processes, or any other type of system apparent to one skilled in the art after reading the present description. For instance, the system may include any type of application which stores information in RAM. Accordingly, it should be noted that method500may be performed by a computing component at (or at least coupled to) the system. Accordingly, the operations included in method500are described as being performed at and by the system. However, any one or more of the operations in method500may be performed in accordance with the present invention in any of the environments depicted inFIGS. 1-4, among others, in various embodiments. For instance, one or more of the operations included in method500may be performed by a processor at a location corresponding to an external process. Of course, more or less operations than those specifically described inFIG. 5Amay be included in method500, as would be understood by one of skill in the art upon reading the present descriptions.

As shown inFIG. 5A, operation502of method500includes receiving incoming information. As data is added to, updated in, removed from, etc. a system, the data itself, as well as metadata which corresponds to the data, are constantly changing. Thus, “information” received by the system may include data and/or metadata (e.g., location information associated with the data), both of which correspond to the system. However, the type of information may vary depending on the type of system. For instance, in different approaches, the information may include data node and/or cache node metadata, write cache, or any other type of information which would be apparent to one skilled in the art after reading the present description.

Moreover, operation504includes splitting the received information between two controllers of a system in a normal operating mode. As described above, incoming information may be split between two or more controllers by a load balancer (e.g., see402ofFIG. 4) of a type known in the art. According to various approaches, the received information may be split differently between the two controllers. For instance, in some approaches the two controllers may be substantially similar, whereby the received information may be split about evenly between the two controllers. In other approaches, the controllers may have different performance characteristics which may be taken into consideration when the information is split between the two, e.g., the controller with the higher performance characteristics may be assigned a greater portion of the received information than the other controller.

Referring momentarily toFIG. 5B, exemplary sub-operations of splitting received information between two controllers are illustrated in accordance with one embodiment, one or more of which may be used to perform operation504ofFIG. 5A. However, it should be noted that the sub-operations ofFIG. 5Bare illustrated in accordance with one embodiment which is in no way intended to limit the invention.

As shown, sub-operation530includes using one of the controllers to process a first portion of the received information, while sub-operation532includes using the other of the controllers to process a second portion of the received information. It should be noted that together, the first and second portions of the received information amount to all of the received information. In other words, the received information is split into the first and second portions, e.g., by a load balancer.

Moreover, sub-operation534includes using the one of the controllers to backup the second portion of the information, while sub-operation536includes using the other of the controllers to backup the first portion of information. The information may be backed up by implementing any backup process and/or procedure which would be apparent to one skilled in the art after reading the present description. For example, one approach of maintaining backups of the data by a controller is to implement high availability. With high availability, the database on the secondary (backup) controller keeps a replicated copy of the data on the primary (other) controller. As a result, each of the controllers is responsible for processing a portion of the received information, while also backing up the remaining portion of the received information. By effectively splitting the load between the controllers, performance of the system is desirably improved. Moreover, information redundancy and/or retention is not sacrificed as all of the received information is also backed up by the controllers. As such, the controllers are able to provide desirably effective performance, while also ensuring that a single controller failure will not result in data, metadata, or system state loss.

Returning toFIG. 5A, after being assigned the information, each of the two controllers store the respective portion of the information in a specified system memory location during the normal operating mode. See operation506. According to an exemplary approach, the specified system memory location may be in RAM, thus the data included in the information may be cache data which is stored in a write cache in the RAM. Accordingly, the system preferably does not operate in a write-through mode while both controllers are operational and functioning normally. In other words, the system does not write the write cache straight to the media, but rather allows for the write cache to form in the specified system memory location, as the data may be recovered despite the occurrence of a system halt event, e.g., as will be described in further detail below. However, according to various other approaches, the specified system memory location may be in any desired type of memory.

By storing this information (data and/or metadata) in a specified system memory location, an embodiment having shared memory capability may be achieved. According to the present description, “shared memory” refers to memory or a namespace which may be attached to, inspected by, and/or accessed (e.g., used) by two or more different processors at two or more different locations. In some approaches, the processors may be central processing units (CPUs) which are part of an overarching multiprocessor computer system. In other approaches, the shared memory may be accessed by two or more processes which are run by two or more processors. Thus, the shared memory may be a location in the operating system memory which multiple processes are able to virtually map to concurrently. Accordingly, shared memory may allow the same memory to be accessed by more than one processor equipped with the specified system memory location, e.g., as will be described in further detail below.

It is also preferred that the information stored in the specified system memory location is protected. Protecting the information may reduce the risk of developing inconsistencies in the information and therefore increases the value of the information. According to one approach, the information may be protected by preventing updates from being performed on the information in the specified system memory location, thereby avoiding the possibility of the system experiencing a halt even during an update of the information and thereby causing the information to become corrupted. Moreover, accessing the information stored in the specified system memory location is preferably conducted in a transactional manner, e.g., such that processes are not left partially completed, multiple outstanding processes are not queued in a buffer, etc. Furthermore, in some approaches the state of the information may be arranged and managed separately from other parts of the system memory, e.g., to avoid any inconsistencies from arising.

With respect to the present description, a system memory location may be “specified” by being named and/or defined, e.g., by a physical address, logical address, identified confines of a particular region of memory, etc. Thus, in some approaches the specified system memory location may be a specified region in memory as would be appreciated by one skilled in the art after reading the present description. Information defining the specified system memory location may be predefined by a user, a system administrator, random selection, etc., and is preferably stored in memory itself (e.g., in a lookup table). Moreover, information defining the specified system memory location may be shared with other locations, or at least made available, thereby enabling the other locations to access the shared memory location and the information stored therein.

Referring still toFIG. 5A, decision507determines whether either of the controllers (e.g., a “first” of the controllers) has entered a failed state. A controller may enter a failed state as a result of a number of different situations. For instance, a controller may enter a failed state as a result of a host-based issue which triggers a failover procedure, a corrupted driver, a power surge, component breakdown, logical errors, etc., or anything else which would be apparent to one skilled in the art after reading the present description. Method500is shown as returning to operation502in response to determining that neither of the controllers have failed (entered a failed state), whereby additional information may be received, split and stored according to operations502,504,506as described above because both controllers are operational and functioning according to the normal operating mode. Yet in other approaches, method500may simply continue to determine whether either of the controllers have entered a failed state, e.g., in situations where no additional information is being received.

However, once a controller has entered a failed state, the controller cannot operate according to the normal operating mode and the system may adjust accordingly by entering a resilient state. For instance, method500is illustrated as proceeding to optional operation508in response to determining that a first of the controllers has entered a failed state. Optional operation508includes storing the metadata in resilient storage in response to a first of the controllers entering a failed state. According to an exemplary approach, “resilient storage” may include non-volatile memory such as flash memory, HDDs, magnetic tape, optical discs, etc. By storing the metadata in resilient storage, the metadata is effectively protected from being lost should the second of the controllers fail as well and/or a system crash occur. Moreover, the system is able to continue functioning at a high performance without introducing noticeable latency, even with only a single operative controller which is a significant improvement over the shortcomings of conventional products discussed above. It is preferred that the changes to the metadata are saved (e.g., stored) in a log structured array format, e.g., as would be appreciated by one skilled in the art after reading the present description. In other words, updates to the metadata may be stored in the resilient storage in the form of log structured updates. For instance, the metadata updates may be written sequentially to a circular buffer.

Referring momentarily now toFIG. 5C, an exemplary sub-processes of storing information in a specified system memory location is illustrated in accordance with one embodiment, one or more of which may be used to perform operation506ofFIG. 5A. However, it should be noted that the sub-operations ofFIG. 5Care illustrated in accordance with one embodiment which is in no way intended to limit the invention.

Here, sub-operation540includes saving snapshots of the metadata in the resilient storage. Snapshots allow for point-in-time versions of the metadata to be captured and stored in memory for later use, e.g., during a failure recovery process. Accordingly, snapshots of the metadata are preferably taken periodically (e.g., after a predetermined amount of time has passed), but in different approaches, snapshots may be taken after a certain amount of metadata has been received by the system, upon request by a user, randomly, etc. Each time a snapshot is taken, it may replace the previously stored snapshot, thereby avoiding an inefficient use of the available memory. In preferred approaches, each newly acquired snapshot is stored in a different storage area than the previously acquired snapshot, e.g., such that the newly acquired snapshot may be fully written to memory before the previously acquired snapshot is actually overwritten. Depending on the approach, the “different storage area” may be a different storage location in the same resilient storage as the previously acquired snapshot, a different storage location in a different resilient storage as the previously acquired snapshot, etc. Accordingly, should a system halt event occur while the newly acquired snapshot is in the process of being written to memory, the previously acquired snapshot may be used in combination with stored metadata updates to restore the system to a state the system was in when the system halt event occurred. Once the newly acquired snapshot has been written to memory in full, the previously acquired snapshot may be overwritten. However, in other approaches each snapshot of the metadata may be stored according to any desired memory management architecture, e.g., as would be appreciated by one skilled in the art after reading the present description. For instance, a newly acquired snapshot may be used to directly overwrite a previously stored snapshot.

In order to retain an updated version of the metadata and not lose any changes to the metadata which occur during I/O operations that happen between the snapshots that are taken, it is preferred that such changes to the metadata are also saved in the resilient storage. It follows that metadata updates which correspond to a most recently acquired snapshot of the metadata are preferably retained (e.g., stored in memory). However, during situations when a newly acquired snapshot is being written to memory, metadata updates corresponding to the newly acquired snapshot and/or the previously acquired snapshot (which is preferably still stored in the resilient storage as described above) may be retained. As a result, should a system halt event occur while the newly acquired snapshot is being written to memory, the retained metadata updates may be used in combination with the newly acquired snapshot and/or the previously acquired snapshot to restore the system. Moreover, by storing metadata updates corresponding to the newly acquired snapshot and/or the previously acquired snapshot, I/O latency issues experienced in conventional products are avoided, thereby resulting in improved performance of the system. Moreover, once the newly acquired snapshot has been fully written to memory as mentioned above, metadata updates corresponding to the previously acquired snapshot may be released to be overwritten. In other words, the metadata updates corresponding to the previously acquired snapshot are represented in the newly acquired snapshot. Therefore, once the newly acquired snapshot has been fully written to the resilient memory, the metadata updates corresponding to the previously acquired snapshot become redundant and may therefore be overwritten as desired, e.g., in order to maintain an efficient use of the available memory.

However, it should also be noted that because one of the controllers is in a failed state, the system is somewhat limited in the achievable throughput. Accordingly, it may be desirable to postpone updates to the metadata which call for a significant amount of system resources. Looking to decision542, it is determined whether any of the changes to the metadata which occur during I/O operations that happen between the snapshots are of a size that is in a predetermined range. In other words, decision542determines whether each of the metadata updates are too large to efficiently process while one of the controllers is in a failed state. One example of a metadata update which may be too large to process while one controller is in a failed state includes a snapshot taken of all the volumes included in the storage system. Moreover, it should be noted that “in a predetermined range” is in no way intended to limit the invention. Rather than determining whether a value is in a predetermined range, equivalent determinations may be made, e.g., as to whether a value is above a threshold, whether a value is outside a predetermined range, whether an absolute value is above a threshold, whether a value is below a threshold, etc., depending on the desired approach.

The flowchart proceeds to sub-operation544in response to determining that a given metadata update is of a size that is in the predetermined range. In other words, flowchart proceeds to sub-operation544in response to determining that a given metadata update is too large to process at the moment (while one of the controllers is in a filed state). There, sub-operation544includes blocking the metadata update. According to some approaches, the update may be blocked temporarily (postponed, stalled, etc.), e.g., whereby the update is stored in a queue until both controllers are operational and the system is in a normal operating mode again. In other approaches the update may be blocked by failing the update altogether.

Alternatively, the flowchart proceeds to sub-operation546in response to determining that a given metadata update is of a size that is in the predetermined range. There sub-operation546includes saving the changes to the metadata corresponding to the update which occurred during an I/O operation between the snapshots taken. As mentioned above, the resilient storage may include different types of memory depending on the given embodiment. However, it is preferred that the changes to the metadata are saved (e.g., stored) in a log structured array format, e.g., as would be appreciated by one skilled in the art after reading the present description. In other words, updates to the metadata may be stored in the resilient storage in the form of log structured updates.

However, it should again be mentioned that the metadata may continue to be stored in the specified system memory location rather than resilient storage. As described above, because the shared memory may allow the same information to be accessed by more than one processor equipped with the specified system memory location, the specified system memory location may be accessed even if the second of the controllers fails and/or a system crash occurs. Thus, although the metadata is preferably stored in the resilient storage while one of the controllers is in a failed state, the data may still be stored in the specified system memory location (e.g., in a write cache therein). Moreover, in some approaches the metadata itself may continue to be stored in the specified system memory location along with the data even after a first controller enters a failed state, e.g., depending on the desired approach.

Although data and/or metadata may continue to be stored in the specified system memory location, the data and/or metadata is not hardened while only one controller is operative. In normal operating mode, data and/or metadata stored by one controller in the specified system memory location is preferably replicated to a physical storage location associated with the other controller for redundancy and data retention purposes. However, data and/or metadata hardening is not performed while only a first controller is functioning, thereby reducing the processing load placed on the system and in view of the fact that the second controller is in a failed state.

FIG. 5further includes determining whether the first controller has been repaired. See decision510. Method500proceeds to operation512in response to determining that the first controller has been repaired, where the first controller is updated with the information received while the first controller was in the failed state. Updating the repaired first controller with the information may be performed by copying the relevant data from the specified system memory location and the relevant metadata from the resilient storage (or specified system memory location depending on the particular approach) to the first controller. Moreover, the system may be returned to the normal operating mode in response to the first controller being successfully (e.g., completely) updated with the information received while the first controller was in the failed state. See operation514. Accordingly, metadata may be stored in the specified system memory location along with the data, e.g., rather than in the resilient storage.

Subsequently, method500may be ended. See operation515. However, it should be noted that method500may progress differently after operation514has been performed in other approaches. For instance, method500may return to operation504after the first controller has been repaired and updated, whereby additional received information may be split and/or assigned to each of the respective controllers. Moreover, additional processes included inFIG. 5may be repeated.

Returning to decision510, method500proceeds to decision516in response to determining that the first controller has not been repaired. There, decision516determines whether the second controller has failed in addition to the first controller. Although method500is illustrated as returning to decision510in response to determining that the second controller has not also entered a failed state, additional steps may be taken. For instance, should additional information be received while the first controller is still in the failed state, the second controller may be used to receive and split the additional information according to any one or more of the processes included in method500. Thus, the storage system remains online and is able to process incoming information despite having one controller which is in a failed state.

However, method500proceeds to operation518in response to determining that the second controller has also entered a failed state. There, operation518includes attaching an external process to the specified system memory location. When both of the controllers in the dual controller storage system are in a failed state, the system has effectively experienced a halt event, or a system crash. According to the present description, a “halt event” or a “system crash” is a situation which causes the system to enter a failed state during which normal operations such as data reading and/or recording may not be performed. Moreover, the system is unable to save data and/or metadata included in the system memory when in a failed state following a halt event, primarily because the system is without any operational controllers.

Once a system halt even has occurred, the system may remain “offline” or not in a normal operation state until the system has been restored, e.g., by repairing or replacing both of the failed controllers. Moreover, restarting the system may also assist in restoring the system. However, in order to restart the system without incurring data and/or metadata loss, it is preferred that the data and/or metadata stored in the specified system memory location be transferred or copied to a separate memory location. As previously mentioned, the system may store data and/or metadata in RAM which is typically associated with volatile types of memory (e.g., such as Dynamic RAM (DRAM) memory modules) which is effectively erased (stored information is lost) if power to the memory is interrupted. Thus, by attaching an external process, or external script, to the specified system memory location after a system halt event has occurred but before the system is restarted, the external process may access the data and/or metadata stored therein by utilizing the shared memory, e.g., as will be described in further detail below, e.g., with reference to method600ofFIG. 6.

With continued reference toFIG. 5A, operation520further includes using the information stored in the specified system memory location to restore the system to a state the system was in when the second controller entered the failed state (the system halt event occurred). Although the information stored in the specified system memory location may be used differently to restore the system depending on the desired embodiment, an exemplary process of restoring the system is disclosed below with reference to any one or more of the processes inFIGS. 6-7A. It follows that any one or more of the processes included inFIGS. 6-7Amay be implemented as a part of performing operation520, as would be appreciated by one skilled in the art after reading the present description.

Moreover, referring still toFIG. 5A, operation521includes recovering the metadata from the resilient storage. As described above, the metadata may be stored in resilient storage in response to a first of the controllers entering a failed state. Thus, the metadata is preferably retrieved from the resilient storage and used to repair the controllers to a state they were in prior to the system halt. According to one approach, the metadata may be copied from the resilient storage to one or both of the repaired controllers and/or memory corresponding thereto (e.g., the specified system memory location). However, it should again be noted that in some approaches metadata may only be stored in the specified system memory location, whereby any one or more of the processes included inFIGS. 6-7Amay be implemented to restore the metadata, e.g., as would be appreciated by one skilled in the art after reading the present description.

It is preferred that operations520and521are performed after (e.g., in response to) the first and/or second controllers have been repaired, thereby desirably enabling the system to successfully resume the normal operating mode once the system has been restored. According to an exemplary approach, which is in no way intended to limit the invention, repairing one or both of the controllers may be achieved by rebooting the contoller(s) in a recovery mode and repairing any of the issues that may have caused the respective controller to initially enter a failed state. Once in recovery mode, preferably both controllers may read a most recently stored snapshot of the metadata from the resilient storage and subsequently read the metadata updates stored after the most recent snapshot was taken. By “reading” the metadata updates stored after the most recent snapshot, the controllers may each play the metadata updates over the snapshot, thereby integrating the two and forming a complete and accurate representation of the metadata up to a point where the system was halted (when the second of the controllers also failed). Thus, the metadata and data write cache may be reinstated for each of the controllers.

Assuming that both of the controllers have been repaired, operation522includes returning the system to the normal operating mode in response to the system being restored. Subsequently, method500may be ended. See operation524. However, it should be noted that method500may return to operation502in some approaches after operation522has been performed. For instance, method500may return to operation502after the system has been restored as well as both controllers having been repaired and updated. As a result, additional information may be received, split and/or assigned to each of the respective controllers, whereby additional processes included inFIG. 5may be repeated. However, assuming that only one of the controllers is repaired and the second controller remains in a failed state, the system may return to a resilient state, under which optional operation508may be re-performed.

It follows that various embodiments described herein are able to achieve a high performance, high resiliency and high availability dual controller storage system at a low price point relative to the achieved throughput, e.g., by implementing any one or more of the processes described herein. Moreover, the external process is able to attach to a specified memory location in the system and extract the information (data and/or metadata) stored in the specified memory location to another storage location which preferably corresponds to the external process. By doing so, the system may be restarted in a recovery mode without losing any of the information from the specified system memory location despite one or even all (e.g., both) the controllers entering a failed state at the same time. Once in a recovery mode, the system may regain access to the information and use it to reform the system to a state it was in at the time the controller failures occurred, thereby desirably avoiding any loss of data and/or metadata from the system as a result of the halt event occurring. In other words, some of the embodiments included herein are able to achieve loss less process state and memory recovery procedures.

However, as previously described, enterprise storage products are also typically subjected to an extremely high reliability and data integrity standards. Yet, conventional storage products are unable to efficiently recover from fatal failure scenarios. For example, enterprise storage products with capacities in the PB range would take days, or even weeks, to recover from a back-up following a fatal failure scenario.

A storage product may suffer from two kinds of fatal failures which include: massive hardware components failures (e.g. massive components suffering from sudden power loss, overheating, etc.), and massive software components and/or node failures.

A software related failure may cause a process to halt. Traditionally, halted processes are considered dead and their online state is lost. This means that in order to resume the process, the storage product either starts over (e.g., refills) from scratch, or from a known point in time that was previously stored in resilient media. Attempts have been made to utilize recovery tools to repair a storage product and avoid recovering from back-ups. However, repairing a storage product using recovery tools is undesirable as well, as doing so typically result in substantial data and metadata loss. Efforts to overcome this loss by continually back-up the data and metadata to resilient storage imposes a severe performance penalty on the system, and in most cases is not even a viable option.

Alternative efforts have been made to back-up the memory and/or process states concurrently on an additional process that will track the state of the main process. The back-up is usually located on another server to provide additional resiliency. Although these efforts do provide additional resiliency, they come at a price to the user. Specifically, the user is taxed with additional processes and resources, communication between processes, delay in operation due to making inter-process updates, etc. Moreover, there is also a very real possibility that whatever caused the original process to halt will also cause the back-up process to halt, thereby essentially making the back-up void in such a scenario.

Further still, some conventional storage products implement a battery in order to reduce the probability of process halt events by allowing the server and the processes to shutdown properly in the event of power loss. Although this scheme may cope with power loss events, it provides no assistance in the event of process halts caused by software failures.

While it may be possible to design the hardware of a storage product such that the correlation of having multiple hardware failures is low (e.g. by installing separate power sources for each server), the nature of some software failures is such that the correlation between the failing software nodes can be high. In other words, the same software failure may trigger rolling node failures. In addition, conventional enterprise storage solutions are often made up of millions of lines of code which increases the probability of a software related failure compared to hardware based failures.

In sharp contrast to the various shortcomings experienced by conventional storage products, some of the embodiments described herein are able to recover a system from a massive software failure without having a user chose between product downtime during recovery and data loss/application inconsistency as experienced with conventional products. In other words, some of the embodiments included herein are able to provide loss-less system recovery processes, e.g., as will be described in further detail below.

Now referring toFIG. 6, a flowchart of a computer-implemented method600for recovering from a system halt event, is shown according to one embodiment. According to different approaches, the system may be a data storage system, an operating system configured to run one or more processes, or any other type of system apparent to one skilled in the art after reading the present description. For instance, the system may include any type of application which stores information in RAM. Accordingly, it should be noted that method600may be performed by a computing component at (or at least coupled to) the system. Accordingly, the operations included in method600are described as being performed at and by the system. However, any one or more of the operations in method600may be performed in accordance with the present invention in any of the environments depicted inFIGS. 1-5C, among others, in various embodiments. For instance, one or more of the operations included in method600may be performed by a processor at a location corresponding to an external process (e.g., see method800ofFIG. 8Abelow). Of course, more or less operations than those specifically described inFIG. 6may be included in method600, as would be understood by one of skill in the art upon reading the present descriptions.

As shown inFIG. 6, operation602of method600includes storing information in a specified system memory location. As described above, as certain data is added to, updated in, removed from, etc. a system, the data itself, as well as metadata which corresponds to the data, are constantly changing. Thus, “information” stored in the specified system memory location preferably includes data and/or metadata (e.g., location information associated with the data), both of which correspond to the system. However, the type of information may vary depending on the type of system. For instance, in different approaches, the information may include data node and/or cache node metadata, write cache, or any other type of information which would be apparent to one skilled in the art after reading the present description. Moreover, the specified system memory location may be in RAM, thus the data included in the information may be cache data. However, according to various other approaches, the specified system memory location may be in any desired type of memory.

Again, by storing this data and metadata in a specified system memory location, an embodiment having shared memory capability may be achieved. According to the present description, “shared memory” refers to memory or a namespace which may be attached to, inspected by, and/or accessed (e.g., used) by two or more different processors at two or more different locations. In some approaches, the processors may be central processing units (CPUs) which are part of an overarching multiprocessor computer system. In other approaches, the shared memory may be accessed by two or more processes which are run by two or more processors. Thus, the shared memory may be a location in the operating system memory which multiple processes are able to virtually map to concurrently. Accordingly, shared memory may allow the same memory to be accessed by more than one processor equipped with the specified system memory location, e.g., as will be described in further detail below.

It is also preferred that the information stored in the specified system memory location is protected. Protecting the information may reduce the risk of developing inconsistencies in the information and therefore increases the value of the information. According to one approach, the information may be protected by preventing updates from being performed on the information in the specified system memory location, thereby avoiding the possibility of the system experiencing a halt even during an update of the information and thereby causing the information to become corrupted. Moreover, accessing the information stored in the specified system memory location is preferably conducted in a transactional manner, e.g., such that processes are not left partially completed, multiple outstanding processes are not queued in a buffer, etc. Furthermore, in some approaches the state of the information may be arranged and managed separately from other parts of the system memory, e.g., to avoid any inconsistencies from arising.

With respect to the present description, a system memory location may be “specified” by being named and/or defined, e.g., by a physical address, logical address, identified confines of a particular region of memory, etc. Thus, in some approaches the specified system memory location may be a specified region in memory as would be appreciated by one skilled in the art after reading the present description. Information defining the specified system memory location may be predefined by a user, a system administrator, random selection, etc., and is preferably stored in memory itself (e.g., in a lookup table). Moreover, information defining the specified system memory location may be shared with other locations, or at least made available, thereby enabling the other locations to access the shared memory location and the information stored therein.

Referring still to method600, operation604includes attaching an external process to the specified system memory location in response to experiencing a system halt event. As previously mentioned, a system may experience a halt event which again, causes the system to enter a failed state during which normal operations such as data reading and/or recording may not be performed. Moreover, the system is unable to save data and/or metadata included in the system memory when in a failed state following a halt event. It should also be noted that any one or more of the approaches described in relation to operation604may be implemented in order to perform operation518above, e.g., depending on the desired embodiment.

Halt events may result from various different situations, but generally are caused by failure situations which the system was not designed to be able to cope with. An exemplary list of system halt events, which is in no way intended to limit the invention, includes situations in which a software program is stuck in an infinite loop, there is at least partial power loss to the system, both controllers of a dual controller storage system fail, a sanity check is failed, a server did not shut down completely, data inconsistency which causes a segmentation fault, assertions caused by defensive programming which may be related to system sanity, etc. Moreover, it is preferred that the system halt event did not negatively affect (e.g., corrupt) the data and/or metadata corresponding to the system, or at least the state of the process. As a result, the data and/or metadata stored in the specified system memory location may be accessed by the external process and preferably used to later restore the system, e.g., as will be described in further detail below.

Once a system halt even has occurred, the system may remain “offline” or not in a normal operation state until the system is restored, e.g., by restarting the system. However, in order to restart the system without incurring data and/or metadata loss, it is preferred that the data and metadata stored in the specified system memory location be transferred or copied to a separate memory location. As alluded to above, systems may store data and/or metadata in RAM which is typically associated with volatile types of memory (e.g., such as Dynamic RAM (DRAM) memory modules) which is effectively erased (stored information is lost) if power to the memory is interrupted. Thus, by attaching an external process, or external script, to the specified system memory location after a system halt event has occurred, the external process may access the data and metadata stored therein by utilizing the shared memory. Moreover, the data and metadata stored in the specified system memory location represents the state of the system at the time the halt even occurred, assuming the halt event did not negatively affect the data and/or metadata, e.g., as a result of a system-wide power outage. By retaining at least a copy of the data and metadata even after the system has been restarted, the system may be restored to a state which corresponds to a point in time when the halt event actually occurred. Therefore, is also preferred that the information is not changed following the halt event and therefore new I/O operations, destage processes, metadata operations, etc. are preferably not implemented while the system is offline. The foregoing achievements are significant improvements over conventional storage products which lose some, if not all, data and metadata in response to a halt event occurring.

An external process may be attached to the specified system memory location if the memory location is defined and/or named, e.g., as would be apparent to one skilled in the art after reading the present description. In other words, the information stored in the specified system memory location may be accessed by more than one process. Once allocated, a specified system memory location may be added to a memory page table of the process attempting to attach thereto, e.g., using a shared-memory attach system call. As a result, a shared memory segment may be a part of the address space of the process, although the actual address of the segment may be different. For instance, the starting address of a shared memory segment in the address space of a first process may be different from the starting address of the shared memory segment in the address space of a second process.

In some approaches, the external process may be attached automatically in response to the system halt even occurring. In other approaches, a request may be sent to a processor implementing the external process, whereby the processor may initiate the attachment of the external process to the specified system memory location. In other words, the process of actually attaching the external process to the specified system memory location may be implemented differently depending on the desired embodiment. According to some approaches, the external process may be a process recovery tool which is connected to a data/cache node memory using the name space of the memory location. The name space may be based on a known identifier for cache descriptors in some instances.

Furthermore, operation606of method600includes sending the information (data and metadata) stored in the specified system memory location to a memory location associated with the external process. It should be noted that the information sent to the memory location associated with the external process is selected to include the relevant information which may be later used to recover the system. In other words, the information copied aside may be selective and may only include the information relevant to perform a system recovery procedure according to any of the approaches described herein. Thus, in preferred approaches, operation606may not include sending all the registers and/or the memory generally contained in a core file.

Again, the external process may be performed by a processor in response to a system halt even occurring. Accordingly, the external process and memory location associated therewith, are preferably removed enough from the system that they are not negatively affected by the system halt event. For example, the external process may be performed by a processor which is geographically separated from the system location, and coupled to the specified system memory location via a wireless network connection.

It follows that the memory location where the data and metadata from the specified system memory location is sent is also preferably removed (e.g., geographically) from the system location. Thus, the data and metadata may be securely retained in the memory location associated with the external process while the system is restarted in order to recover from the system halt event and eventually return to a normal operating mode. However, it should be noted that the memory location associated with the external process is not so removed from the system that a connection cannot be made between the system and the external process and/or the memory location associated therewith. It is desirable that the information may be sent back to the system from the memory location associated with the external process in order to restore the system, e.g., as will be described in further detail below.

Accordingly, once the data and metadata from the system have been transitioned to the memory location associated with the external process, operation608includes restarting the system in a recovery mode. In the recovery mode, certain features and/or functions of the system may be deactivated. For example, the system may not be able to receive or perform I/O operations when functioning in recovery mode. However, in some approaches I/O operations may be received and stored in a buffer, e.g., to be performed after the system has been returned to a normal mode of operation. By deactivating certain features and/or functions, the system may be able to recover and return to a state the system was in at the point in time the halt event occurred without being prompted with any other operations. This may prevent the halt event from repeating at the system, e.g., particularly in the case of software-based halt events.

Furthermore, by restarting the system, data and metadata stored in certain types of memory is lost as a result of the supply power being cut during the restart process. For example, data and/or metadata stored in volatile memory such as DRAM, static RAM (SRAM), etc. is lost as a result of interrupting the power supplied to the volatile memory as a part of the restart process. It may therefore be desirable to reconstruct the data and/or metadata previously included in the memory as a result of restarting the system in a recovery mode before performing additional operations.

Accordingly, once the system is in recovery mode, method600includes retrieving the information from the memory location associated with the external process. See operation610. In some approaches, a request for the information (data and/or metadata) may be sent to the memory location associated with the external process. In response to receiving the request, the external process may send the information back to the system via a connection existing therebetween, make the information available (e.g., unlocked) and the system may subsequently extract the information, provide the system with the location where the information is stored, etc. In other approaches, the external process may automatically detect when the system has been restarted in recovery mode and may send the information in response to making such a detection, the external process may simply inform the system that the information is ready for retrieval, etc.

Moreover, once the information has been retrieved by the system from the memory location associated with the external process, operation612includes using the retrieved information to restore the system to a state the system was in when the system halt event occurred. In other words, the retrieved information may be used to repopulate the system memory and/or destaged to storage. When the halt event occurs, there is no organized state in which the information is stored. Thus, sending the information to the memory location associated with the external process and using the retrieved information to restore the system are performed differently. The information may be loaded into memory and/or replayed as I/O operations, e.g., as will be described in further detail below.

Once the system has been restored to a memory state the system was in when the halt event occurred, operation614includes switching the system to a normal mode of operation. Once in a normal mode of operation, the system may be able to receive and/or perform I/O operations, initiate and/or perform programs, etc., depending on system configurations. As previously mentioned, the system may be a data storage system which is capable of receiving, storing, reading, etc. data. However, in other approaches the system may be an operating system configured to run one or more processes. It follows that any one or more of the operations and sub-processes described herein may be performed on different types of relevant (e.g., compatible) systems, e.g., depending on the desired approach.

Looking now toFIG. 7A, exemplary sub-processes of using the retrieved information to restore the system are illustrated in accordance with one embodiment, one or more of which may be used to perform operation612ofFIG. 6. However, it should be noted that the sub-processes ofFIG. 7Aare illustrated in accordance with one embodiment which is in no way intended to limit the invention.

As mentioned above, the information retrieved from the external process may include data as well as metadata which corresponds to the data. Accordingly, sub-operation700includes loading metadata from the retrieved information into the specified system memory location. The same specified system memory location used prior to the halt event may be reused to store the metadata, but in some approaches a different system memory location may be specified (e.g., defined and named) as a result of experiencing the halt event. The metadata may be loaded into the specified system memory location by transferring the metadata files to the memory location as would be appreciated by one skilled in the art after reading the present description. Moreover, upon loading the metadata into the specified system memory location, the metadata state of the process may be recovered. In some approaches, the metadata state of the process may be recovered by implementing a recovery function which allows the system to read and/or implement the information such that the system returns to the state it was in just as the halt event occurred, e.g., as would be appreciated by one skilled in the art after reading the present description.

Referring still toFIG. 7A, sub-operation702includes loading the data from the retrieved information into a separate memory location, while sub-operation704includes playing back the data from the separate memory location as I/O operations performed on the system. According to one approach, the separate memory location may be located in RAM, but may be located in any type of memory depending on the desired approach. By playing back the data as I/O operations performed on the system, the data may be used to repopulate the specified system memory location and thereby return the system to a state the system was in when the halt event occurred. According to an exemplary approach, which is in no way intended to limit the invention, information stored in one or more files at the memory location associated with the external process may be played back by running a remote procedure call in a node that receives the name(s) of the one or more files. Information may thereby be read from the one or more files and internally handled by the system as a standard I/O operation.

As previously mentioned, these achievements are significant improvements over conventional products which lose all data and metadata changes since a last snapshot of the system memory was taken, or lose the data and metadata altogether as a result of the halt event. Accordingly, various embodiments described herein are able to significantly improve the process of recovering from a system halt event.

In some situations, the data and/or metadata stored in the specified system memory location may be corrupted, e.g., as a result of the system halt event. Thus, inconsistencies may form in the data and/or metadata before it is sent to the memory location associated with the external process in response to the system halt event occurring. It follows that it may be desirable to examine the data and/or metadata before it is reimplemented in the storage system after the system has been restarted in recovery mode. Examining the data and/or metadata may prevent any inconsistencies from being transferred back to the system after the system has been restarted and restored (e.g., see operation612above).

According to some approaches the data and/or metadata may be examined at the storage system. For instance, the information may be examined while it is stored in the separate memory location and before it is used to restore the system. In other approaches, the information may be examined as it is received from the memory location associated with the external process and before it is stored in the separate memory location. Accordingly, looking now toFIG. 7B, exemplary sub-processes of retrieving the information from the memory location associated with the external process are illustrated in accordance with one embodiment, one or more of which may be used to perform operation610ofFIG. 6. However, it should be noted that the sub-processes ofFIG. 7Bare illustrated in accordance with one embodiment which is in no way intended to limit the invention.

Decision750includes determining whether any inconsistencies exist in the retrieved information. In some approaches, inconsistencies in the retrieved information may correspond to whether the information is in-tact after the halt event occurred. In other words, the manner in which the halt event caused the system to stop may have an effect on whether inconsistencies exist in the retrieved information. This determination may be made at any point after a halt event occurs. However, it is preferred that decision750is performed after the information has been returned to the system. According to one approach, decision750may be performed as a part of a recovery process which loops between descriptors which include data concerning which partition, disk, block, etc. of memory the retrieved information has been stored in the system. Moreover, for each descriptor, the integrity of the corresponding information may be checked in order to determine whether any inconsistencies exist.

As shown, the flowchart ofFIG. 7Breturns to operation612in response to determining that no inconsistencies exist in the retrieved information. Accordingly, the data and metadata included in the information retrieved from the memory location associated with the external process may be used to reconstruct the system as described above.

Alternatively,FIG. 7Bproceeds to sub-operation752in response to determining that at least one inconsistency does exist in the retrieved information. There, sub-operation752includes creating an improved version of the retrieved information. An improved version of the retrieved information may be created by first analyzing the information. According to some approaches, the information may be analyzed by determining the integrity of the information. In other approaches, the information may be analyzed by comparing it to anticipated values, checking if the information complies with standards associated with the system, determining whether an overall size (amount of memory) of the information matches a size of the information prior to the halt event occurring, etc.

After it is created, the improved version of the retrieved information is preferably used to restore the system rather than the version of the information retrieved directly from the memory location associated with the external process. By doing so, any inconsistencies in the information are not retained after transitioning the information back to the specified system memory location. Thus, althoughFIG. 7Bshows the flowchart proceeding to operation612after sub-operation752has been performed, it should be noted that the improved version of the retrieved information is preferably used moving forward in operations612and614when applicable. In other words, the “retrieved information” used to restore the system in operation612may include the information retrieved directly from the memory location associated with the external process, or the improved version of the retrieved information, e.g., depending on whether inconsistencies are determined to be in the information.

Although it may be desirable in some approaches that the data and/or metadata is examined at the system, e.g., after it has been received from the memory location associated with the external process, it should be noted that the information may be examined for inconsistencies differently according to various other approaches. For instance, in some approaches, the data and/or metadata may be examined at the memory location associated with the external process prior to being returned to the specified system memory location, e.g., as will be described in further detail below.

As mentioned above, the operations and/or sub-processes included herein may be performed in accordance with the present invention in any of the environments depicted inFIGS. 1-7B, among others, in various embodiments. Thus, looking now toFIG. 8A, a flowchart of a computer-implemented method800for helping recover a system from a halt event, is shown according to one embodiment. According to different approaches, the system may be a data storage system, an operating system configured to run one or more processes, or any other type of system apparent to one skilled in the art after reading the present description. For instance, the system may include any type of application which stores information in RAM. However, it should be noted that method800is preferably performed by a computing component at (or at least coupled to) a location corresponding to the external process. Accordingly, the operations included in method800are described as being performed at the location corresponding to the external process. Moreover, it should be noted that more or less operations than those specifically described inFIG. 8Amay be included in method800, as would be understood by one of skill in the art upon reading the present descriptions.

As shown inFIG. 8A, operation802of method800includes detecting that a system halt event occurred at a system corresponding to the external process. Moreover, in response to making such a detection, operation804includes attaching to a specified memory location at the system. As described above, a system memory location may be specified by being named and/or defined, e.g., by a physical address, logical address, identified confines of a particular region of memory, etc. Thus, in some approaches the specified system memory location may be a specified region in memory as would be appreciated by one skilled in the art after reading the present description. Information defining the specified system memory location may be predefined by a user, a system administrator, random selection, etc., and is preferably stored in memory itself (e.g., in a lookup table). Moreover, information defining the specified system memory location may be shared with other locations, or at least made available, thereby enabling the other locations to access the shared memory location and the information stored therein. Accordingly, the external process may attach (or be attached) to the specified system memory location by using the information defining the memory location's name, location, memory type, etc., despite the external process being external to (e.g., physically removed from) the system.

In some approaches, the external process may attach to the specified system memory location via a wireless connection such as a wireless Internet connection, a wide area network (WAN), a Broadband Global Area Network (BGAN), a LAN, etc. In other approaches, the external process may attach to the specified system memory location via a wired network connection such as an Ethernet connection, a fiber-optic connection, etc.

With continued reference to method800, operation806includes extracting information stored in the specified system memory location. As described above, “information” may at least include data and/or metadata (e.g., location information associated with the data), both of which correspond to the system. According to one approach, the external process may extract the information by reading the information and creating a copy of the information, whereby the copy of the information may be further used by the external process. Moreover, the information may remain in the specified system memory location after it has been extracted by the external process in some approaches. However, in other approaches the external process may delete the information from the specified system memory location after it has been extracted, the system itself may delete the information after it has been extracted, the information may be indicated as invalid to be overwritten during a next garbage collection operation, etc.

Moreover, operation808includes storing the information extracted from the specified system memory location in local memory. It should be noted that the term “local memory” is preferably with respect to the external process itself rather than the system. Thus, in different approaches, the extracted information may be stored in different mediums associated with (and preferably accessible by) the external process, which may include magnetic disk, a solid state drive, one or more file locations, etc. As described above, the local memory is preferably removed enough from the system that it is not at risk of being affected by system halt events, but is preferably close enough (geographically and/or logically) to the system that establishing a connection therebetween is likely. Storing the data and/or metadata in the local memory may be achieved by writing the information according to the memory format. For example, information stored in local SSD memory may be sent to a buffer in a SSD controller. According to another example, storing information on a magnetic disk may include implementing a disk_dd command or any other disk write utility which would be apparent to one skilled in the art after reading the present description.

Decision810includes determining whether the system has been restarted in a recovery mode. As described above, a system is preferably restarted in a recovery mode after a halt event occurs, e.g., in order to reconstruct the system, but preferably not until after any desired data is transitioned to a secure memory location. For instance, data stored in volatile memory may be lost as a result of restarting the system, as doing so may terminate the power supplied to the memory at least momentarily. Whether the system has been restarted in a recovery mode may be determined in a number of different ways. For example, in some approaches, the external process may detect that the system has been restarted in a recovery mode as a result of receiving a request from the system for the information. Thus, it should be noted that method800may alternatively wait to receive a request from the system for the data/metadata, and then send the information in response to receiving the request. In other approaches, the external process may determine that the system has been restarted in recovery mode as a result of the system attempting to reconnect to the external process via a wired and/or wireless connection during a reboot process of the system, or any other way of making such a determination as would be apparent to one skilled in the art after reading the present description.

As shown, method800includes sending the information back to the specified system memory location in response to determining (e.g., detecting) that the system has been restarted in a recovery mode. See operation812. Again, once the system has been restarted in a recovery mode, the data and/or metadata previously included therein may be used to restore the system to a state the system was in at the point in time the halt event occurred, e.g., according to any of the approaches described above. In other approaches, the information may be sent to one or more files and/or memory location the system accesses in response to being restarted in a recovery mode, and the system itself may reimplement the information in the specified memory location from the one or more files and/or memory location. Moreover, after all of the information has been sent back to the system, method800may include detaching the external process from the specified system memory location. See optional operation814. It should also be noted that although operation812includes sending the information back to the system, in other embodiments the system may initiate the transfer of and/or effectively pull the information from the memory associated with the external process.

However, returning to decision810, method800continues to loop back and perform decision810in response to each time it is determined that the system has not been restarted in a recovery mode. It may be undesirable to send the information back to the system before it has been restarted in a recovery mode as doing so may cause the information to be lost once the system is restarted. For instance, in some approaches the specified system memory location may be in RAM. According to different approaches, method800may wait a predetermined amount of time, until a user input is received, until a condition has been met, etc., before decision810is performed again after it is determined that the system has not been restarted in a recovery mode. As a result, method800may avoid unnecessary resource consumption which may otherwise result from performing decision810at too high of a frequency.

Again, in some approaches it may be desirable that the information is examined for inconsistencies at the memory location associated with the external process (e.g., by the external process) before being stored and/or returned to the specified system memory location. Looking toFIG. 8B, exemplary sub-processes of extracting information stored in the specified system memory location are illustrated in accordance with one embodiment, one or more of which may be used to perform operation806ofFIG. 8A. However, it should be noted that the sub-processes ofFIG. 8Bare illustrated in accordance with one embodiment which is in no way intended to limit the invention.

Decision850includes determining whether any inconsistencies exist in the extracted information. In some approaches, inconsistencies in the retrieved information may correspond to whether the information is in-tact after the halt event occurred. In other words, the manner in which the halt event caused the system to stop may have an effect on whether inconsistencies exist in the retrieved information. This determination may be made at any point during and/or after the information has been extracted from the specified system memory location by the external process following a halt event. According to one approach, decision850may be performed as a part of a recovery process which loops between descriptors which include data concerning which partition, disk, block, etc. of memory associated with the external process the extracted information has been stored in. Moreover, for each descriptor, the integrity of the corresponding information may be checked in order to determine whether any inconsistencies exist.

As shown, the flowchart ofFIG. 8Breturns to operation808in response to determining that no inconsistencies exist in the extracted information. Accordingly, the data and metadata included in the information extracted from the specified system memory location may be stored in a memory location associated with the external process, and may later be used to reconstruct the system according to any of the approaches described herein.

Alternatively,FIG. 8Bproceeds to sub-operation852in response to determining that at least one inconsistency does exist in the extracted information. There, sub-operation852includes creating an improved version of the extracted information. An improved version of the extracted information may be created by first analyzing the information. According to different approaches, the information may be analyzed by determining the integrity of the information, comparing it to anticipated values, checking if the information complies with standards associated with the system, determining whether an overall size (amount of memory) of the information matches a size of the information prior to the halt event occurring, etc.

After it is created, the improved version of the extracted information is preferably stored in the memory location associated with the external process rather than the version of the information directly extracted from the specified system memory location. By doing so, any inconsistencies in the information are not retained after the information is extracted and/or transitioned back to the specified system memory location during a recovery process. Thus, althoughFIG. 8Bshows the flowchart proceeding to operation808after sub-operation852has been performed, it should be noted that the improved version of the retrieved information is preferably used moving forward in method800when applicable. In other words, the “information” sent back to the specified system memory location in operation812may include the information extracted directly from the specified system memory location, or the improved version of the extracted information, e.g., depending on whether inconsistencies are determined to be in the information during the extraction process.

It follows that various embodiments described herein are able to recover a system following a halt event, e.g., by attaching to the halted system using an external process. Moreover, the external process is able to attach to a specified memory location in the system and extract the information (data and/or metadata) stored in the specified memory location to another storage location which preferably corresponds to the external process. By doing so, the system may be restarted in a recovery mode without losing any of the information from the specified system memory location. Once in a recovery mode, the system may regain access to the information and use it to reform the system to a state it was in at the time the halt event occurred, thereby desirably avoiding any loss of data and/or metadata from the system as a result of a halt event occurring. In other words, some of the embodiments included herein are able to achieve loss less process state and memory recovery procedures.

Any one or more of the embodiments described herein may be performed on each halted (failed) data/cache node, preferably in order to ultimately recover the entire system to a state the system was in just as the halt event occurred. Moreover, the operations and/or sub-processes included herein may be initiated by an individual (e.g., a system administrator, a user, etc.) in response to detecting that a halt event has occurred at the system, or initiated automatically (e.g., by the system, the external process, a system management controller, etc.) in response to a halt event occurring.