The subject matter of this disclosure is generally related to data storage systems and more particularly to detection of lost writes and inconsistencies.
Data storage systems such as storage area networks (SANs) and network-attached storage (NAS) are used to maintain large data sets and contemporaneously support many users. Such data storage systems may implement a variety of features to maintain data integrity and data availability while protecting against data loss. Data integrity is the accuracy and consistency of data. Maintaining data integrity may include detection and correction of data corruption. Data corruption can occur for a variety of reasons. Data storage systems typically include networked computing nodes that manage arrays of drives such as hard disk drives (HDDs) and solid-state drives (SSDs) that may experience uncorrectable data errors due to bit flips and sector failures. Data storage systems are generally tolerant of such errors because error detection and correction codes (EDAC) and other features may be used to detect and correct the errors. However, some data errors, such as lost writes, are resistant to detection by features designed to detect bit flips and sector failures.
All examples, aspects and features mentioned in this document can be combined in any technically possible way.
Some implementations comprise: defining a plurality of sector signature patterns; embedding a first one of the sector signature patterns with a slice of data; separately storing a metadata record indicative of the sector signature pattern embedded with the slice of data; and responsive to a read to the slice of data: performing a data integrity check using the embedded sector signature pattern and the metadata record. Some implementations comprise, responsive to a write to the slice of data, selecting a second one of the sector signature patterns and replacing the embedded sector signature pattern by embedding the second one of the sector signature patterns with the slice of data as updated by the write. Some implementations comprise defining the plurality of sector signature patterns with an algorithm. Some implementations comprise defining the plurality of sector signature patterns with horizontal parity values. Some implementations comprise defining the plurality of sector signature patterns with an order in which each sector signature and each horizontal parity value changes when a next sector signature pattern in the order is selected and embedded. Some implementations comprise defining the plurality of sector signature patterns with diagonal parity values. Some implementations comprise defining the plurality of sector signature patterns with an order in which each sector signature and each horizontal parity value and each diagonal parity value changes when a next sector signature pattern in the order is selected and embedded. In some implementations separately storing the metadata record indicative of the sector signature pattern embedded with the slice of data comprises storing a key. In some implementations performing the data integrity check using the embedded sector signature pattern and the metadata record comprises performing a pattern-to-key lookup.
Some implementations comprise: a storage system comprising a plurality of computing nodes and managed drives, at least one of the computing nodes comprising a sector signature transition controller comprising: transition logic that embeds a first one of a plurality of sector signature patterns with a slice of data and separately stores a metadata record indicative of the sector signature pattern embedded with the slice of data; and integrity check logic responsive to a read to the slice of data to perform a data integrity check using the embedded sector signature pattern and the metadata record. In some implementations the transition logic is responsive to a write to the slice of data to select a second one of the sector signature patterns and replace the embedded sector signature pattern by embedding the second one of the sector signature patterns with the slice of data as updated by a write. In some implementations an algorithm calculates the plurality of sector signature patterns. In some implementations the sector signature patterns comprise horizontal parity values. In some implementations the plurality of sector signature patterns comprises an order in which each sector signature and each horizontal parity value changes when a next sector signature pattern in the order is selected and embedded. In some implementations the sector signature patterns comprise diagonal parity values. In some implementations the plurality of sector signature patterns comprises an order in which each sector signature and each horizontal parity value and each diagonal parity value changes when a next sector signature pattern in the order is selected and embedded. In some implementations the metadata record indicative of the sector signature pattern embedded with the slice of data comprises a key. In some implementations the integrity check logic performs a pattern-to-key lookup.
Some implementations comprise a computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for using a computer system to perform a data integrity check, the method comprising: defining a plurality of ordered sector signature patterns comprising sector signature parity; embedding a first one of the sector signature patterns with a slice of data; separately storing a key indicative of the sector signature pattern embedded with the slice of data; and responsive to a read to the slice of data: performing a data integrity check using the embedded sector signature pattern and the metadata record. In some implementations the method further comprises, responsive to a write to the slice of data, selecting a second one of the sector signature patterns and replacing the embedded sector signature pattern by embedding the second one of the sector signature patterns with the slice of data as updated by the write.
Other aspects, features, and implementations may become apparent in view of the detailed description and figures.
The terminology used in this disclosure is intended to be interpreted broadly within the limits of subject matter eligibility. The terms “disk” and “drive” are used interchangeably herein and are not intended to refer to any specific type of non-volatile storage media. The terms “logical” and “virtual” are used to refer to features that are abstractions of other features, e.g. and without limitation abstractions of tangible features. The term “physical” is used to refer to tangible features that possibly include, but are not limited to, electronic hardware. For example, multiple virtual computers could operate simultaneously on one physical computer. The term “logic” is used to refer to special purpose physical circuit elements, firmware, software, computer instructions that are stored on a non-transitory computer-readable medium and implemented by multi-purpose tangible processors, and any combinations thereof.
Aspects of the inventive concepts are described as being implemented in a data storage system that includes host servers and a storage area network (SAN), which may also be referred to as a storage array. Such implementations should not be viewed as limiting. Those of ordinary skill in the art will recognize that there are a wide variety of implementations of the inventive concepts in view of the teachings of the present disclosure. Some aspects, features, and implementations described herein may include machines such as computers, electronic components, optical components, and processes such as computer-implemented procedures and steps. It will be apparent to those of ordinary skill in the art that the computer-implemented procedures and steps may be stored as computer-executable instructions on a non-transitory computer-readable medium. Furthermore, it will be understood by those of ordinary skill in the art that the computer-executable instructions may be executed on a variety of tangible processor devices, i.e. physical hardware. For practical reasons, not every step, device, and component that may be part of a computer or data storage system is described herein. Those of ordinary skill in the art will recognize such steps, devices, and components in view of the teachings of the present disclosure and the knowledge generally available to those of ordinary skill in the art. The corresponding machines and processes are therefore enabled and within the scope of the disclosure.
The SAN 100 includes one or more bricks 104. Each brick includes an engine 106 and one or more drive array enclosures (DAEs) 108, 110. Each DAE includes managed drives 101 which are non-volatile media such as, without limitation, solid-state drives (SSDs) based on EEPROM technology such as NAND and NOR flash memory and hard disk drives (HDDs) with spinning disk storage media. Drive controllers may be associated with the managed drives as is known in the art. Each engine 106 includes a pair of interconnected computing nodes 112, 114, which may be referred to as “storage directors.” Each computing node includes resources such as at least one multi-core processor 116 and local memory 118. The processor may include central processing units (CPUs), graphics processing units (GPUs), or both. The local memory 118 may include volatile media such as dynamic random-access memory (DRAM), non-volatile memory (NVM) such as storage class memory (SCM), or both. Each computing node includes one or more host adapters (HAs) 120 for communicating with the hosts 103. Each host adapter has resources for servicing input-output commands (IOs) from the hosts. The resources may include processors, volatile memory, and ports via which the hosts may access the SAN. Each computing node also includes a remote adapter (RA) 121 for communicating with other storage systems. Each computing node also includes one or more drive adapters (DAs) 128 for communicating with the managed drives 101 in the DAEs 108, 110. Each drive adapter has processors, volatile memory, and ports via which the computing node may access the DAEs for servicing IOs. Each computing node may also include one or more channel adapters (CAs) 122 for communicating with other computing nodes via an interconnecting fabric 124. The paired computing nodes 112, 114 of each engine 106 provide failover protection and may be directly interconnected by communication links. An interconnecting fabric 130 enables implementation of an N-way active-active backend. A backend connection group includes all drive adapters that can access the same drive or drives. In some implementations every drive adapter 128 in the SAN can reach every DAE via the fabric 130. Further, in some implementations every drive adapter in the SAN can access every managed drive 101 in the SAN.
Data associated with the hosted application instances running on the hosts 103 is maintained on the managed drives 101. The managed drives 101 are not discoverable by the hosts 103 but the SAN 100 creates a production volume 140 that can be discovered and accessed by the hosts. The production volume is a logical storage device that may be referred to as a source device, production device, or production LUN, where the logical unit number (LUN) is a number used to identify logical storage volumes in accordance with the small computer system interface (SCSI) protocol. From the perspective of the hosts 103, the production volume 140 is a single drive having a set of contiguous fixed-size logical block addresses (LBAs) on which data used by the instances of the host application resides. However, the host application data is stored at non-contiguous addresses on various managed drives 101. Metadata that maps between the LBAs and addresses in shared memory and the managed drives is maintained by the computing nodes.
In order to maintain data integrity, the sector signature transition controller 102 (
A data integrity check is performed by calculating a sector parity value and comparing the metadata sector parity value with the calculated sector parity value. For example, in integrity check 1 the calculated sector parity value of 0 matches the previously stored metadata sector parity value of 0, which indicates data integrity for all parity group members. If, as a result of data corruption, the sector signature value of one of the sectors becomes 3 as indicated in integrity check 2, the calculated sector parity value is 1. The calculated sector parity value of 1 fails to match the metadata sector parity value of 0, which indicates loss of data integrity. Individual ESS and MD SS values for the sectors can then be compared to determine which sectors require correction. Advantageously, the data integrity check that does not indicate loss of integrity is completed without comparing the ESS and MD SS values of each and every parity group member. The XOR calculations are not computationally burdensome so the integrity check is efficient even as the number of sectors in the parity group is scaled up. However, although such parity-based data integrity checks enhance efficiency, corruption of multiple sectors can create a misleading parity value match. For example, if, as a result of data corruption, the sector signature values of two of the sectors becomes 3 as indicated in integrity check 3, then the calculated sector parity value is 0. The calculated sector parity value of 0 matches the metadata sector parity value of 0, which incorrectly indicates data integrity.
One way to avoid false indications of data integrity is to manage sector signature assignment and transition collectively. Rather than individually incrementing each embedded sector signature value, all sector signature values are set to values corresponding to a predetermined pattern. More specifically, multiple patterns are predetermined, and all sector signature values are updated by transitioning to a different pattern. Corresponding pattern keys are maintained separately as part of the metadata. Key-to-pattern mappings enable the transition controller to efficiently determine an expected pattern from a key to perform a data integrity check. The patterns are selected such that every sector signature within the pattern changes each time a different pattern is used on the same parity group, split or slice. The pattern may further be selected such that the parity values change each time a different parity group is used. In some implementations a new pattern is used only when the entire slice is written. Individual sector signature may be updated for sub-slice writes. In other implementations a new pattern is used for every write.
A sector signature generation algorithm for full slice writes with even-numbered RAID data member widths is described below.
Algorithm parameters:
Calculate:
Variables:
if (M<=1) then SS(M, S):=(M+SV+(idiv(S, (2{circumflex over ( )}SB)))) mod SSMax
if W<=(SSMax) then
if SSMax<W<=(2{circumflex over ( )}(SB+1)) then
if (2{circumflex over ( )}(SB+1))<W<=(2{circumflex over ( )}(SB+2)) then
When an IO to the slice is received as indicated in step 308, subsequent processing is dependent on the IO type. In the case of a write a different pattern is selected as indicated in step 310 and the data and pattern are written to the slice. The key-to-pattern lookup is utilized to generate the ESS, HP, and DP values. The ESS values are changed as indicated in the different pattern even if the corresponding sector data has not changed. The IO is then completed as indicated in step 312, e.g. sending an ACK, etc. Selection of a different pattern may include selecting the pattern corresponding to the next key in the incremental/cyclical order. In the case of a read the sector signature parity values are used to perform a data integrity check as indicated in step 314. If integrity is confirmed, then the IO is completed as indicated in step 312. If integrity is lost, then the embedded sector signatures are used to find and correct corrupted sectors as indicated in step 316 so the IO can be completed as indicated in step 312. A pattern-to-key lookup is utilized during recovery. If no matching key is found, then the data is considered inconsistent even if the data XORs into parity properly. Subsequent IOs to the slice are similarly processed beginning back at step 308.
Specific examples have been presented to provide context and convey inventive concepts. The specific examples are not to be considered as limiting. A wide variety of modifications may be made without departing from the scope of the inventive concepts described herein. Moreover, the features, aspects, and implementations described herein may be combined in any technically possible way. Accordingly, modifications and combinations are within the scope of the following claims.
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