Indempotent journal mechanism for file system

Description of equivalent WO 2007103513 A2

IDEMPOTENT JOURNAL MECHANISM FOR FILE SYSTEM

TECHNICAL FIELD

0003[0001] Embodiments of the invention relate to file system management. More particularly, embodiments of the invention relate to techniques for use of a file management system having distributed metadata servers that may be used, for example, in a system that may support video editing, video archiving and/or video distribution.

BACKGROUND

0005[0002] In general, a file system is a program (or set of programs) that provides a set of functions related to the storage and retrieval of data. The data may be stored, for example, on a non-volatile storage device (e.g., hard disk) or volatile storage device (e.g., random access memory). Typically, there is a set of data (e.g., file name, access permissions) associated with a file that is referred to as "file metadata." The file metadata can be accessed during the process of accessing a file.

BRIEF DESCRIPTION OF THE DRAWINGS

0007[0003] The invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements.

0008[0004] Figure 1 is a conceptual illustration of a journal.

0009[0005] Figure 2 is a conceptual illustration of one embodiment of a journal entry.

0010[0006] Figure 3 is a flow diagram of one embodiment of a technique for performing data modification operations using journal entries.

0011[0007J Figure 4 is a block diagram of one embodiment of an electronic system.

0012[0008] Figure 5 is a block diagram of one embodiment of a system that may utilize a file system with distributed metadata servers.

DETAILED DESCRIPTION

0014[0009] In the following description, numerous specific details are set forth. However, embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Journal Entries

0015[0010] In general, a journal includes a listing of operations performed by a metadata server. The journal allows other metadata servers (or other system devices) to repeat the operations performed by the metadata server. Thus, the journal may be used to synchronize data modification operations and support a coherent data system.

0016[0011] In one embodiment, the journals described above may be utilized to provide an idempotent journal mechanism for the file system. In general, "idempotent" means that repeated applications of one or more operations have the same result as a single application of the one or more operations. Thus, in the system described herein, multiple applications of the operations in the journals may have the same effect as a single application of the operations in the journals. One advantage is that the state of the file system may not be exactly defined prior to application of the operations in the journals.

0017This may allow the operations to be applied without corrupting the metadata.

0018[0012] As described in greater detail below, the following mechanism may be utilized to provide an idempotent journaling. In one embodiment, each entry in the journals includes a sequence number. The sequence number should be unique and sequence numbers should be monotonically increasing. In one embodiment, each file system object

0019(e.g., file, file slice, data segment) may include the journal sequence number (JSN) for the journal entry corresponding to the operation that created the file system object. The JSN becomes part of the file metadata. In one embodiment, within the journal a file system object may be referenced by its name and the JSN of the journal the created the file. The combination of the file name and JSN will provide an absolutely unique reference within the file system.

0020[0013] In one embodiment, the JSN must be unique within the file system for the life of the file system; it can be therefore implemented as a number with a very large dynamic range (i.e. 64 bits). Even when journal entries are generated at a rate of 10,000 entries per second, a 64-bit JSN would allow 4 million years before it wraps.

0021[0014] In one embodiment, each time a journal is executed the file name and JSN doublet are compared to the file name and JSN of the target file. If the JSNs do not match the reference is considered invalid and the operation is ignored.

0022J0015] Figure 2 is a conceptual illustration of one embodiment of a journal entry. In one embodiment, for each operation recorded an entry such as the entry illustrated in

0023Figure 2 may be generated and maintained as part of the journal. In one embodiment, each entry 200 may include the fields illustrated in Figure 2 as well as additional fields. In alternate embodiments, different fields may be used.

0024JOOl 6] In one embodiment, when a data modification operation is performed a journal entry 200 is generated. Entry 200 will include journal sequence number (JSN) field 210 to store a JSN corresponding to entry 200. As described above, the JSN will be a unique large (e.g., 64-bit) number that is selected from a predetermined pattern (e.g., monotonically increasing). As another example described in greater detail below, the JSN may be used as a technique to provide an idempotent journal mechanism. [0017] Entry 200 may further include data modification operation field 220 to store a data modification operation corresponding to entry 200. The data modification operation may be any type of data modification operation, for example, a file creation operation, a data write operation. Entry 200 may also include parameters 250 that correspond to the data modification operation stored in data modification filed 220. The parameters stored in parameter field 250 may be any type of parameters relevant to the data modification operation stored in data modification field 220. The parameters may vary based on the type of operation stored in the entry.

0025[0018] In one embodiment, each entry includes journal doublet 290, which includes file name field 230 and file creation JSN field 240. File name field 230 may store a file name or other file identifier. File creation JSN field 240 may store a JSN corresponding to the data modification operation that created the file identified by the file name. In one embodiment, journal doublet 290 may be used to identify a file to which a data modification operation may be applied.

0026[0019] Because a file name is generally not required to be unique through all time it is possible that a file may be created, deleted and another file created with the same name in a short period of time. If so, and a data modification operation targeting the first file is performed in the second file the file system will be corrupted. However, by using journal doublet 290, an idempotent journal mechanism may be provided.

0027[0020] Figure 7 is a flow diagram of one embodiment of a technique for performing data modification operations using journal entries. A metadata server may perform a data modification operation that is stored in an entry of a journal for synchronization purposes or for file system restoration purposes. Before performing the data modification operation, the metadata server may determine the journal doublet (described with respect to Figure 2) including the file name and the file creation JSN from the entry, 710. [0021] The journal doublet may be compared with the file creation JSN of the file having a name matching the journal doublet, 720. If the file names and file creation JSN match, 730, the data modification operation from the entry can be performed, 750. If the file names and file creation JSN do not match, 730, the data modification operation from the entry is ignored, 740.

0028System Overview

0029(0022] Figure 1 is a block diagram of one embodiment of a system that may utilize a file system with distributed metadata servers. In one embodiment, the various components of the system of Figure 1 are interconnected using standard interconnection technologies (e.g., Ethernet, Gigabit Ethernet). For example, in one embodiment, switching fabric 150 may be a Gigabit Ethernet (or 10 Gigabit Ethernet) interconnection architecture to allow the various components of system 100 to communicate with each other.

0030[0023] In one embodiment, multiple client devices (e.g., 130, 132, ... 138) may be interconnected via switching fabric 150. Client devices may allow users to access and/or otherwise utilize data available through system 100. In one embodiment, the client devices are computer systems having sufficient storage and input/output capability to allow users to manipulate data stored in various servers. For example, in a multimedia system, the client devices may allow users to access stored multimedia files as well as edit or otherwise utilize the multimedia files.

0031[0024] In one embodiment, the system of Figure 1 may include any number of metadata servers, each of which may store metadata for files that are stored in the system. In one embodiment, a metadata server may be responsible for managing the file system and may be the primary point of contact for client devices. In one embodiment, each client device may include file system driver (FSD) software that may present a standard file system interface, for accessing files the system.

0032(0025] In one embodiment, the various electronic systems of Figure 1 (e.g., data servers, metadata servers, clients) as an electronic system such as, for example, the electronic system of Figure 2. The electronic system illustrated in Figure 2 is intended to represent a range of electronic systems, for example, computer systems, network access devices, etc. Alternative systems, whether electronic or non-electronic, can include more, fewer and/or different components. [0026] Electronic system 200 includes bus 201 or other communication device to communicate information, and processor 202 coupled to bus 201 to process information. While electronic system 200 is illustrated with a single processor, electronic system 200 can include multiple processors and/or co-processors. Electronic system 200 further includes random access memory (RAM) or other dynamic storage device 204 (referred to as memory), coupled to bus 201 to store information and instructions to be executed by processor 202. Memory 204 also can be used to store temporary variables or other intermediate information during execution of instructions by processor 202. [0027] Electronic system 200 also includes read only memory (ROM) and/or other static storage device 206 coupled to bus 201 to store static information and instructions for processor 202. Data storage device 207 is coupled to bus 201 to store information and instructions, Data storage device 207 such as a magnetic disk or optical disc and corresponding drive can be coupled to electronic system 200.

0033[0028] Electronic system 200 can also be coupled via bus 201 to display device 221 , such as a cathode ray tube (CRT) or liquid crystal display (LCD), to display information to a user. Alphanumeric input device 222, including alphanumeric and other keys, is typically coupled to bus 201 to communicate information and command selections to processor 202. Another type of user input device is cursor control 223, such as a mouse, a trackball, or cursor direction keys to communicate direction information and command selections to processor 202 and to control cursor movement on display 221. Electronic system 200 further includes network interface 230 to provide access to a network, such as a local area network.

0034[0029] Instructions are provided to memory from a storage device, such as magnetic disk, a read-only memory (ROM) integrated circuit, CD-ROM, DVD, via a remote connection (e.g., over a network via network interface 230) that is either wired or wireless providing access to one or more electronically-accessible media, etc. In alternative embodiments, hard-wired circuitry can be used in place of or in combination with software instructions. Thus, execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions. [0030] An electronically accessible medium includes any mechanism that provides (i.e., stores and/or transmits) content (e.g., computer executable instructions) in a form readable by an electronic device (e.g., a computer, a personal digital assistant, a cellular telephone). For example, a machine-accessible medium includes read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals); etc.

0035Conclusion

0036[0031] Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

0037[0032] In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.