Reducing data storage system I/O bandwidth via read-once point in time copy

A computer-implemented method includes: detecting a read access to one or more data tracks of a target data storage module; and setting a value of one or more bits in response to detecting the read access to the one or more data tracks, each of the one or more bits being associated with one of the one or more data tracks. The value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the read access was detected. Corresponding systems and computer program products are similarly disclosed, all of which advantageously improve storage system performance by reducing I/O bandwidth via preventing unnecessary copy operations.

BACKGROUND

The present invention relates to managing data storage systems, and more specifically, this invention relates to reducing input/output (I/O) bandwidth in data storage systems by preventing unnecessary copy operations.

In conventional data storage systems, particularly data storage systems including plural storage modules, devices, etc. and where data are routinely copied from one module, device etc. to another, rigorous copying of changes on the one module, device, etc. over to the other is generally advantageous for maintaining consistency between the data on each module, device, etc.

However, in situations where the data need not be copied over, e.g. because data consistency on one of the two modules is not critical, this conventional rigorous copy regime increases load on the storage system's I/O bandwidth without commensurate benefit to the data storage system as a whole. In addition, this increased load results in the undesirable wasting of energy resources, which is both economically and environmentally detrimental.

Accordingly, it would be advantageous to provide systems and techniques enabling a reduction in I/O bandwidth load by avoiding unnecessary copy operations in data storage systems.

SUMMARY

In one embodiment, a computer-implemented method includes: detecting a read access to one or more data tracks of a target data storage module; and setting a value of one or more bits in response to detecting the read access to the one or more data tracks, each of the one or more bits being associated with one of the one or more data tracks. The value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the read access was detected.

In another embodiment, a computer program product for read-once point-in-time copy includes a computer readable storage medium having program instructions embodied therewith. The computer readable storage medium is not a transitory signal per se, and the program instructions are executable by a storage system manager to cause the storage system manager to perform a method. The method includes detecting a read access to one or more data tracks of a target data storage module; and setting a value of one or more bits in response to detecting the read access to the one or more data tracks, each of the one or more bits being associated with one of the one or more data tracks. The value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the read access was detected.

In yet another embodiment, a system includes a processor and logic integrated with and/or executable by the processor. The logic is configured to: detect a read access to one or more data tracks of a target data storage module; and set a value of one or more bits in response to detecting the read access to the one or more data tracks, each of the one or more bits being associated with one of the one or more data tracks. The value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the read access was detected.

DETAILED DESCRIPTION

The following description discloses several preferred embodiments of systems, methods and computer program products for managing data storage systems, and more specifically, for reducing input/output bandwidth in data storage systems by preventing unnecessary copy operations.

In one general embodiment, a computer-implemented method includes: detecting a read access to one or more data tracks of a target data storage module; and setting a value of one or more bits in response to detecting the read access to the one or more data tracks, each of the one or more bits being associated with one of the one or more data tracks. The value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the read access was detected.

In another general embodiment, a computer program product for read-once point-in-time copy includes a computer readable storage medium having program instructions embodied therewith. The computer readable storage medium is not a transitory signal per se, and the program instructions are executable by a storage system manager to cause the storage system manager to perform a method. The method includes detecting a read access to one or more data tracks of a target data storage module; and setting a value of one or more bits in response to detecting the read access to the one or more data tracks, each of the one or more bits being associated with one of the one or more data tracks. The value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the read access was detected.

In yet another general embodiment, a system includes a processor and logic integrated with and/or executable by the processor. The logic is configured to: detect a read access to one or more data tracks of a target data storage module; and set a value of one or more bits in response to detecting the read access to the one or more data tracks, each of the one or more bits being associated with one of the one or more data tracks. The value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the read access was detected.

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, modules, etc. 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, modules, devices, etc. 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, which may be implemented as physical devices, virtual storage modules, etc. as would be understood by a person having ordinary skill in the art upon reading the present descriptions.

The storage system manager312may communicate with the 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.

Referring now toFIG. 4A, a conventional storage system400is shown. As shown, the conventional storage system400includes a host402coupled to a source410, which is in turn coupled to a target420. The source410and target420each comprise a plurality of data tracks, some of which have data written thereto (i.e. tracks412,422) and others which are empty (i.e. tracks414,424).

In practice, the conventional storage system400implements copy-on-write functions (also referred to as copy source-to-target functions, point in time copy functions, etc. as would be understood by a skilled artisan upon reading the present descriptions) in response to the source410receiving a write request, instruction, command, etc.404for data to be written to one or more track(s)416of the source410. Using copy-on-write functionality, the request and/or any necessary data are propagated406to the target420in corresponding target track(s)426.

With continuing reference to a conventional storage system400as shown inFIG. 4B, this copy-on-write functionality is performed without regard to whether data tracks422of the target420have been offloaded408to long term storage430, e.g. tape-based storage media430. Rather, the conventional storage system400is ignorant of any previous or concurrent offload process408. As a result, during and after an offload process408, the conventional storage system400propagates406to a corresponding data track(s) of the target420those changes made to data tracks416of the source410that occur in response to source410receiving a write command, request, instruction, etc.404from the host402.

While this conventional procedure of ignoring long term offload processes408advantageously maintains consistency between data tracks416of the source410and data track(s)426of the target420, it also results in increased I/O bandwidth, which may require data or applications relying on data be suspended or otherwise interfered with during the copy-on-write process. In the modern era where energy efficiency is a prime consideration in the operation of data storage systems, any unnecessary increase in I/O bandwidth undesirably wastes energy resources.

Accordingly, the presently disclosed inventive concepts are configured, in various embodiments, to reduce I/O bandwidth and system hold-up associated with the problem presented by conventional storage systems' ignorance of offload processes.

One embodiment of an inventive storage system within the scope of the present disclosures is represented schematically via storage system450depicted inFIGS. 4C and 4D. As shown, the inventive storage system450includes a host402, source410and target420. As shown, the inventive storage system450is in the process of performing an offload408to long term storage media430.

Of course, the presently disclosed inventive embodiments may be implemented to advantage in scenarios other than during an offload408, as would be understood by skilled artisans upon reading the present descriptions. Indeed, the presently disclosed inventive embodiments may be employed to particular advantage in any situation where data tracks on a target420need not be maintained in close consistency with changes to corresponding data tracks on a source410. For example, the presently described inventive concepts may be useful in situations where one or more data tracks of the target420are designated “read-only,” in some embodiments.

As will be further understood by a person having ordinary skill in the art upon reading the present descriptions, in embodiments where long term storage media430include tape media or other sequential access media, the offload process408may include sequentially writing data from a plurality of data tracks of the source420to the long term storage media430. As such, and as shown inFIG. 4D, the offload process408may involve reading data tracks of the target420in a sequential manner, indicated by the dashed lines and offload progress indicators Oi(offload initiation), Oc(offload current); and Of(offload final).

Regardless of whether the offload process408utilizes sequential, random, or other access techniques, a storage manager (e.g. storage system manager312as shown inFIG. 3) is made aware of the offload process408, including which data track(s)428of the target420have been offloaded to the long term storage media430and which data tracks429remain to be offloaded, but have not yet been completed. In preferred implementations, this allows the storage manager to reduce or eliminate I/O bandwidth associated with performing copy-on-write operations406in response to receiving a write command, request, instruction, etc.404which relates to a data track416of the source410, and the corresponding data track426of the target420has already been offloaded to the long term storage media430.

In particularly preferred embodiments, the implementation is accomplished via a target bit map (TBM)415, as shown particularly inFIGS. 4C and 4D. In brief, upon completing an offload operation408for a data track426,428of the target420, the bit value associated with the offloaded data track426,428may be modified to indicate data have already been updated, obviating the need for the subsequent copy-on-write operation406(as indicated inFIG. 4D).

For instance, according to one exemplary embodiment the TBM is managed by the storage system manager (e.g. storage system manager312as shown inFIG. 3), preferably a disk storage system manager. Using techniques known in the art, the storage system manager may detect a read operation performed on one or more data track(s) of a target420.

In response to detecting the read operation, the storage system manager may modify a bit associated with the one or more data track(s) represented in the TBM415, the modification may indicate that the data in those one or more data track(s) are up-to-date. From the perspective of the copy-on-write process406, this effectively indicates the impending copy-on-write operation406has already been completed, obviating the impending copy-on-write operation406for at least the duration of the offload process408. Accordingly, a commensurate amount of I/O reduction and resource consumption is achieved, improving the function of the storage system itself.

As particularly shown inFIG. 4C, in one approach the TBM415includes a plurality of binary bits having a value of 0 or 1. The bits may initially be set to “1” to indicate data should be copied from the source to the target. The storage manager controlling the storage system450detects a read access to the target420by, e.g., a process or a storage manager of or coupled to the storage media430.

Detecting this read access is an indication that the corresponding tracks have been offloaded to the storage media430and the storage manager controlling the storage system accordingly modifies the corresponding bit in the TBM415to have a value of “0.” Subsequently, as shown inFIG. 4D, when a copy-on-write process406awould otherwise have caused the previously-read track on the target420to be updated, based on detecting the corresponding bit in the TBM415has a value of “0”, the copy-on-write process406ais not performed, and associated I/O bandwidth consumption is avoided.

On the other hand, if no read access has been detected by the storage system manager, then a copy-on-write process406bmay advantageously be performed, copying data from a source track416to a corresponding target track426and ensuring data are consistent before they are read during the offload process408. Accordingly, tracks offloaded in a duration between Oiand Ocmay be inconsistent with the corresponding tracks on the source after completion of the upload process, to the extent copy-on-write operations406awould otherwise have been performed. However, this result is tolerable in the contexts presented herein, as well as equivalents that would be understood by a skilled artisan upon reading the present descriptions.

Tracks may also be evaluated on the storage media430after the offload process408is complete to determine which of the offloaded data are consistent with the post-offload state of the corresponding tracks on the source410, in various approaches.

Those having ordinary skill in the art will also appreciate that the presently disclosed inventive embodiments are also useful in the context of a copy-on-write process optimized by caching. In such approaches, a copy-on-write operation406may be delayed pending completion of an offload process408. Again, noting the presently disclosed concepts are not limited to the context of an offload process408, while in conventional storage systems utilizing caching the subsequent copy-on-write process406would occur after offload408and consume commensurate resources and I/O bandwidth, storage systems implementing the presently disclosed configuration and techniques would ignore the copy-on-write process406and avoid the consumption associated with the post-offload copy-on-write process406.

In more approaches, it may be advantageous to utilize the TBM in a similar manner, but instead of (or in addition to) preventing copy-on-write processes, cache hints can be given to the storage system manager, enabling the storage system manager to delay offloading data that is about to be read by the tape system. Holding off on these offload processes can prevent the usage of internal bandwidth in order to achieve the copy-on-write action that would otherwise have been performed at that time.

In the storage systems disclosed herein, according to some embodiments it may be advantageous to keep as much data as possible in a cache. However, accessing data in cache may require accessing storage media, which is associated with greater I/O consumption than accessing data in memory. Accordingly, by leveraging a priori knowledge that data tracks of a particular target are subject to a future offload, will be designated read-only, or otherwise may tolerate inconsistency to some extent, it is possible to reduce I/O associated with retrieving data from disk in the course of the offload process when using caching.

In such embodiments, it may be particularly advantageous to utilize the TBM to determine which data stored in cache have been offloaded, and which data have yet to be offloaded, in order to selectively delay offloading those data stored in cache and which have yet to be offloaded. In more embodiments, data stored in memory which have yet to be offloaded may or may not be delayed in a similar manner, as would be understood by a person having ordinary skill in the art upon reading the present descriptions.

In a similar manner, it is possible to utilize multiple bitmaps to provide finer granularity of awareness with respect to the status of particular data tracks on a source, target, etc. regarding data validity. In particular, it may be advantageous to track whether (1) data have been read from the target (e.g. in the course of an offload process); and (2) data have been written to the target (e.g. in the course of a copy-on-write process which may be applicable to a data track not yet read during an offload process).

Accordingly, in one embodiment a first bitmap may be utilized to keep track of whether particular data tracks on the source have been read by the storage medium to which data are (or will be) offloaded. Based on the first bitmap, copy-on-write processes intended to be applied to tracks on the target which have already been offloaded may be prevented as described above. Similarly, a second bitmap may be utilized to keep track of those tracks which have already been written to on the target, e.g. tracks downstream of the current position of an offload process on the target volume. Utilizing these bitmaps in combination, it is possible to determine which data on the target volume (post-offload) and which data on the storage medium are consistent with the state of the corresponding data on the source at the time the offload process is completed. The first and/or second bitmaps are preferably target bit maps, in various approaches.

For instance, those tracks that were read during the offload process but for which no subsequent write operation/request/command was received at the source accurately reflect the status of the data post-offload and may be considered consistent. This consistency determination may be accomplished by comparing the bit values for the various tracks in the first and second bitmaps, in various approaches.

One consequence of implementing the presently disclosed inventive concepts is that a future write that would have caused a copy-on-write under conventional techniques and systems, is instead ignored if the data was offloaded to, and/or read by, long term storage media. As a result, the data is no longer consistent with the updated data on the source. In the case of tape off-load, this consequence may be acceptable, and in fact desired in situations where the inconsistent data will not be relied upon going forward, e.g. will not be read again. Accordingly, in preferred embodiments this solution should be an option for the user to select. For instance, in one approach the presently disclosed “read-once” functionality should be user-enabled/disabled via a toggle setting available, e.g. in a configuration interface such as a command line interface, graphical user interface, etc.

Another consequence of implementing the presently disclosed inventive embodiments is that they disallow reverse restore capabilities, i.e. forcing the data from the target back into the source, with respect to at least those data tracks for which a copy-on-write process was ignored.

Now referring toFIG. 5, a flowchart of a method500is shown according to one embodiment. The method X00may be performed in accordance with the present invention in any of the environments depicted inFIGS. 1-3, 4C and 4D, among others, but not the environments depicted inFIGS. 4A and 4B, in various embodiments. Of course, more or less operations than those specifically described inFIG. 5may be included in method500, as would be understood by one of skill in the art upon reading the present descriptions.

Each of the steps of the method500may be performed by any suitable component of the operating environment. For example, in various embodiments, the method500may be partially or entirely performed by a storage system manager, e.g. storage system manager312as shown inFIG. 3, or some other device having one or more processors therein. The processor, e.g., processing circuit(s), chip(s), and/or module(s) implemented in hardware and/or software, and preferably having at least one hardware component may be utilized in any device to perform one or more steps of the method X00. Illustrative processors include, but are not limited to, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc., combinations thereof, or any other suitable computing device known in the art.

As shown inFIG. 5, method500may initiate with operation502, where access, or an attempt to access, one or more data tracks of a target data storage module are detected. The access or access attempt is preferably a read access rather than a write access, and is preferably detected by a storage system manager managing the storage system of which the target data storage module is a part. More preferably, the read access and/or access attempt are received at the target data storage module and sent from a long-term storage module, preferentially a tape storage device.

In response to detecting the access or access attempt, in operation504method500includes setting a value of one or more bits, where each of the one or more bits is associated with one of the one or more data tracks on the target data storage module. Preferably, the value of the one or more bits is set to a value configured to prevent a copy-on-write operation being applied to the one or more data tracks to which the access or attempt for access was detected.

Of course, the method500may additionally and/or alternatively include any other functionality as described herein without departing from the scope of the present disclosure. Preferred embodiments may include any one or more of the following additional and/or alternative features.

As described above, the one or more bits are preferably stored in a TBM, and preferably are associated with data tracks in a one-to-one relationship such that the TBM represents the data tracks of the target storage module.

Setting the value of bits for which access was obtained or attempted to the value configured to prevent copy-on-write operations being applied to the associated data tracks may include determining a value of each of the one or more bits in response to detecting the read access to the one or more data tracks; determining whether the value of each of the one or more bits is the value configured to prevent the copy-on-write operation being applied to the one or more data tracks to which the read access was detected; and in response to determining the value of one or more of the one or more bits is not the value configured to prevent the copy-on-write operation being applied to the one or more data tracks to which the read access was detected, performing the setting operation.

In more approaches, detecting the access may include determining whether the read access is requested by a long term data storage module coupled to the target data storage module. As will be appreciated based on reading the above descriptions, in some approaches it is advantageous to permit copy-on-write operations where the access or attempt is not from a long-term storage module, as this may indicate that the data on the target storage module will be needed in the future and consistency should be maintained. Accordingly, in some approaches it is particularly advantageous to either determine the identity of the module/device requesting access to the target storage module, and/or permit a user to manually define whether or not to prevent copy-on-write operations as described herein, e.g. by setting a flag.

In various approaches, the presently disclosed inventive techniques may include detecting a pending copy-on-write request applicable to one or more of the one or more data tracks of the target data storage module. The detection of pending copy-on-write requests is optional, but may be advantageous to selectively prevent copy-on-write operations based on other criteria than merely detecting an access or access attempt. In other embodiments, additional computational efficiency and I/O reduction may be possible by omitting any attempt to detect incoming or pending copy-on-write requests, and instead relying simply on the access or access attempt to trigger copy-on-write prevention functionality. Skilled artisans will appreciate the advantageous applicability of each embodiment in various real-world contexts, upon reading the present descriptions.

For instance, in one approach preventing copy-on-write may include determining the pending copy-on-write request is applicable to one or more of the data tracks to which the read access was detected, the determining being based on evaluating the value of the one or more bits associated with the one or more data tracks to which the write request is applicable; and preventing the pending copy-on-write request based on the result of the evaluation. In particular, if the evaluation reveals the value of the bit associated with the target storage system data track is the value configured to prevent copy-on-write (e.g. a value of 0), then the copy-on-write is preferably prevented. If the evaluation instead reveals the value of the bit associated with the target storage system data track is not the value configured to prevent copy-on-write (e.g. a value of 1), then the copy-on-write is preferably permitted.

As alluded to above, consistency determination may also be a useful aspect of various embodiments of the presently disclosed inventive techniques. For instance, in one approach consistency determination may include determining a consistency of the one or more data tracks of the target storage module relative to one or more corresponding data tracks of a source storage module. The determining is based, at least in part, on evaluating bits in two bit maps, preferably TBMs. Each of the bits in one of the bit maps is associated with a data track on the target storage module, while each of the bits on a second of the bit maps is associated with one a corresponding data track of the source storage module. Each of the bits in the first bit map indicates whether access was made or attempted to the associated data track of the target storage module; while each of the bits in the second bit map indicates whether a write operation was applied to the corresponding data track of the source storage module with which the bit is associated.

Alternatively, the bits of each bit map may be associated with data tracks of the target storage module, and bits of one bit map may track the access status of the corresponding data tracks, while bits of the other bit map may track incoming copy-on-write requests received from the source storage module by the target storage module.