Patent Application
20070078890
The present invention generally relates to write-once read-many (WORM) storage and in particular to an object that facilitates creation and maintenance of items such as indices, database logs, and audit trails in WORM storage.
As critical data are increasingly stored in electronic form, it is imperative that the critical data be stored reliably in a tamper-proof manner. Furthermore, a growing subset of electronic data (e.g., electronic mail, instant messages, drug development logs, medical records, etc.) is subject to regulations governing long-term retention and availability of the data. Recent high-profiled accountability issues at large public companies have further caused regulatory bodies such as the Securities and Exchange Commission (SEC) to tighten their regulations. For instance, Securities Exchange Commission Rule 17a-4, which went into effect in May 2003, specifies storage requirements for email, attachments, memos, and instant messaging as well as routine phone conversations. A requirement in many such regulations is that data must be stored reliably in non-erasable, non-rewritable storage such that the data, once written, cannot be altered or overwritten. Such storage is commonly referred to as WORM (Write-Once Read-Many) storage as opposed to WMRM (Write-Many Read-Many) storage, which can be written many times.
Critical data requires some form of organization such that all of the data relevant to an enquiry can be promptly discovered and retrieved, typically within days and sometimes even within hours. Scanning all of the data in a large volume of data to discover entries that are relevant to an enquiry is not practical. Instead, the data requires organization with some form of direct access mechanism such as an index. Such access mechanisms require storage in WORM storage to prevent the access mechanisms from being tampered. Otherwise, an adversary may modify the direct access mechanism to logically modify the data; e.g., hide an object by removing an index entry or replace an object by modifying the index entry for the original object.
Furthermore, there is often a need to log small amounts of data to WORM storage, for instance, to maintain database logs or non-alterable audit trails of activity in a system. To manage index mechanisms and logs such that they cannot be tampered, some form of WORM storage is required that allows adding new index/log entries while preventing any of the committed entries from being modified.
Although conventional WORM storage technology has proven to be useful, it would be desirable to present additional improvements. Conventional WORM storage systems do not efficiently support index mechanisms and logs. Conventional WORM storage ensures that an object (e.g. file, object, block) is immutable after the object has been committed into the WORM storage system. To store index structures and logs in WORM storage, creation of new objects is required whenever new entries are committed, incurring both performance and space overhead and degrading locality of reference. To improve performance and space overhead, entries can be committed less frequently. However, entries that have not been committed are not guaranteed to be immutable or even to be persistent. Alternatively, a large collection of data can be indexed in a batch. However, this batch index is not available until an entire collection of data is received and indexed. Moreover, as data is added over a period of time, the system creates many indices, each of which may need to be searched to find a particular piece of data.
What is therefore needed is a system, a computer program product, and an associated method for providing an object to support index structures, logs, and audit trails in WORM storage. The need for such a solution has heretofore remained unsatisfied.
The present invention satisfies this need, and presents a system, a service, a computer program product, and an associated method (collectively referred to herein as “the system” or “the present system”) for providing an object to support index structures, logs, and audit trails in WORM storage. The present system comprises an object storage system that supports a storage object comprising differing levels of protection. In one embodiment, the level of protection for the storage object can be upgraded.
In addition to metadata typically associated with an object, the present system maintains, for each storage object, an indication of its level of protection against modification. In an embodiment, the storage object comprises the following levels of protection: modifiable (a mutable object), not modifiable (an immutable object), or appendable (an appendable object). The present system allows a mutable object to be arbitrarily modified. The present system ensures that an immutable object cannot be modified. The present system guarantees that the contents of the appendable object cannot be modified but can be appended with new data; data that is appended to the appendable object becomes immutable.
In one embodiment, the present system enables the level of protection associated with an object, i.e. the type of an object, to be upgraded. The mutable object can be changed to an appendable object; the appendable object can be changed to an immutable object. The immutable object cannot be changed to an appendable object or a mutable object. The appendable object cannot be changed to a mutable object. In this way, data that is committed to be immutable cannot be changed by changing the type of the storage object in which the data is stored.
In one embodiment, the level of protection is valid for a predetermined period of time. In another embodiment, the present system upgrades the level of protection after a predetermined period of time.
The storage object of the present system enables implementation of a WORM index system. An index is divided into index segments each comprising zero or more index entries. The index entries in each index segment are stored in an appendable object. Once written to the appendable object, the written index entries are immutable; i.e., the index entries cannot be changed. A new index entry can be added to the appendable object. Once the new index entry is written to the appendable object, the new index entry is immutable. In this manner, a WORM index cannot be modified to logically modify data that have been indexed, i.e., added to the index.
The storage object of the present system enables implementation of WORM log. The WORM log comprises an appendable object. Entries to the WORM log are written into the appendable object. As entries are written, the entries become immutable. To close the WORM log, the type of the appendable object is upgraded to immutable. In this manner, a WORM log cannot be modified to change entries that have been logged, i.e., added to the log. The WORM logs can be divided into fixed size or fixed duration parts for ease of management. Each of these parts can be stored in an appendable object.
The present system may be embodied in a utility program such as an object storage utility program. The present system provides means for the user to identify a set of data for storage in one or more storage objects of the object storage utility program. The set of data may be, for example, a record, an index, a log, an audit trail, etc. The present system provides means for specifying performance criteria associated with the set of data such as, for example, a level of protection for the data, an expiration time for a log, or a time at which a storage object upgrades a level of protection. The present system further provides means for the user to invoke the object storage utility program to generate and maintain data such as, for example, a record, an index, a log, an audit trail, etc.
The various features of the present invention and the manner of attaining them will be described in greater detail with reference to the following description, claims, and drawings, wherein reference numerals are reused, where appropriate, to indicate a correspondence between the referenced items, and wherein:
The following definitions and explanations provide background information pertaining to the technical field of the present invention, and are intended to facilitate the understanding of the present invention without limiting its scope:
Appendable: Capable of receiving new data that is appended to existing data. An object of appendable type comprises immutable data that can be appended with new data. Once appended, the new data becomes immutable (WORM).
Immutable or WORM: Incapable of modification or deletion. An object of immutable type-cannot be modified, overwritten, or deleted.
Mutable: Capable of modification. An object of mutable type can be modified, overwritten, or deleted.
The storage system logic 20 comprises a data manager 40, a protection manager 45, and an object manager 50. System 10 further comprises a storage media such as, for example, a hard disk 60 and a tape 70. Clients such as clients 80, 90 access system 10 through a network 95 or direct links.
System 10 comprises a storage object. The storage object comprises differing levels of protection against modification. For example, the object manager 50 maintains, for each storage object, an indication of type; e.g., mutable, immutable, or appendable.
The protection manager 45 allows a storage object of mutable type (further referenced herein as a mutable object) to be arbitrarily modified. The protection manager 45 protects a storage object of immutable type (further referenced herein as an immutable object) such that it cannot be changed in any way. The protection manager 45 protects the contents of a storage object of appendable type (further referenced herein as an appendable object) such that the contents cannot be changed. The protection manager 45 allows data to be appended to the appendable object; data appended to the appendable object becomes immutable. The data manager 40 handles the flow of data into and out of the system.
The object manager 50 allows a level of protection for the storage object to be upgraded by, for example, modifying the type of the storage object. For example, the mutable object can be changed to the appendable object; the appendable object can be changed to the immutable object. The immutable object cannot be changed to the appendable object or the mutable object. The appendable object cannot be changed to the mutable object. In this way, data that is committed to be immutable cannot be changed by changing the type of the storage object in which the data is stored.
In one embodiment, object manager 50 determines whether a storage object with the specified name already exists. If so, system 10 returns a failure to the create request. In another embodiment, object manager 50 appends a version number to the specified name if an object with the specified name already exists in the system. In a further embodiment, determining whether an object already exists in the system comprises determining whether an object with the specified name is in the process of being created. In yet another embodiment, the object name is not specified in the request to create an object. Instead, object manager 50 determines a name to assign the object and system 10 returns the assigned name to the user of the system.
If the current type of the requested storage object is immutable (decision step 325), the type of the requested storage object cannot be changed. Consequently, system 10 returns the error “request failed” (step 315). If the current type of the requested storage object is appendable (decision step 330), object manager 50 determines whether the update type request is a request to change from an appendable type to an immutable type or a request to change from an appendable type to a mutable type (decision step 335). An appendable object can only be changed to an immutable object.
If the update type request attempts to change an appendable object to a mutable object, system 10 returns the error “request failed” (step 315). If the update type request attempts to change an appendable object to an immutable object (decision step 335), object manager 50 performs the requested update type request on the storage object (step 340). If, at decision step 330, the current type is not appendable, the current type is mutable (step 345). A mutable object can be changed to either an appendable object or an immutable object. Consequently, object manager 50 performs the update type request (step 340). In one embodiment, object manager 50 stores a time a storage object is created, a time a storage object becomes an appendable object, and a time the storage object becomes an immutable object.
If the current type of the requested storage object is immutable (decision step 425), the requested storage object cannot be modified or overwritten. Consequently, system 10 returns the error “request failed” (step 415). If the current type of the requested storage object is appendable (decision step 430), protection manager 45 determines whether the write request is an append request or an overwrite request (decision step 435). If the write request is an overwrite request, system 10 returns the error “request failed” (step 415). The contents of an appendable object cannot be changed or overwritten. If the write request is an append request (decision step 435), data manager 40 performs the requested write request on the storage object (step 440). If at decision step 430 the current type is not appendable, the current type is mutable (step 445). A mutable object can be modified or overwritten. Consequently, data manager 40 performs the write request (step 440).
When a commit of an operation occurs, system 10 ensures that any effects of that operation are made persistent, even across system crashes or power failures. In one embodiment, all operations are automatically committed after they are performed.
To store an index entry, data structure manager 25 uses a method of the index to determine a destination location of the index entry (step 515). For example, if the index is a hash table, a destination location of the index entry is identified by computing a hash function on the index key of the index entry. Data structure manager 25 identifies which appendable object corresponds to the determined destination location (step 520). Data structure manager 25 determines whether the identified appendable object exists (decision step 525). If not, data structure 25 creates an appendable object corresponding to the destination location determined in step 525 (step 530). Data structure manager 25 appends the index entry to the appendable object (step 535). Any previous index entry remains immutable in the appendable object, providing an immutable, appendable index structure. In one embodiment, entries in each object are ordered by time of insertion rather than by an index key.
Data structure manager 25 looks up the appendable object corresponding to the selected candidate location (step 625). If the appendable object is not found (decision step 630), data structure manager 25 determines whether any additional candidate locations correspond to the index entry (decision step 635). If additional candidate locations are identified, data structure manager 25 selects a next candidate location and repeats steps 620, 625, and 630. If no additional candidate locations are identified (decision step 635), no results are found for the search and System 10 returns a message “Search Key Not Found” (step 645).
If data structure manager 25 finds an appendable object corresponding to the selected location (decision step 630), data structure manager 25 performs a search for the search key (step 650) using, for example, a linear scan. If the search key is not found (decision step 655), system 10 returns a message “Search Key Not Found” (step 645). If the search key is found, system 10 returns the found index entry (step 660).
In one embodiment, the index may comprise multiple entries corresponding to the search key. Data structure manager 25 searches the candidate locations to return all the index entries corresponding to the search key.
Each log operation can be committed immediately after the log operation has been performed. In one embodiment, several operations are committed in a group to improve performance. Typically, a log is divided into fixed size or fixed duration parts for ease of management. Each of these parts can be stored in a storage object of System 10.
It is to be understood that the specific embodiments of the invention that have been described are merely illustrative of certain applications of the principle of the present invention. Numerous modifications may be made to the system and method for providing an object to support data structures in WORM storage described herein without departing from the spirit and scope of the present invention.
Moreover, while the present invention is described for illustration purpose only in relation to WORM storage, it should be clear that the invention is applicable as well to, for example, storage that is write-once for a specified period of time after the data is written. In other words, it should be clear that an immutable object may be protected from modification only for a specified period of time. Furthermore, while the invention is described for illustration purpose only in relation to mutable, immutable and appendable files, it should be apparent that the invention includes other levels of protection against modification.
It should also be clear that the invention comprises different methods of adding data to an object, such as, for example, appending, prepending, etc. The idea of dividing an object into segments, allowing segments to be added to an object, and allowing data to be added to segments within an object also falls within the scope of the current invention. Furthermore, while the present invention is described for illustration purpose only in relation to index and log structures, it should be clear that the invention is applicable as well to, for example, any other incrementally growing data structure in WORM storage. Furthermore, it should be apparent that the object of the present invention could be a file, block, or other collection of data.
