Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
2001-08-23
2004-04-13
Kim, Hong (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S112000, C714S006130, C707S793000
Reexamination Certificate
active
06721862
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improvements in methods and circuits for backing up data, and, more particularly, to improvements in methods and circuits for reliably and safely backing up selected data during the operation of a network of the type which has a data monitoring facility and includes at least a block-level storage protocol, or the like, and, still more particularly, to improvements in methods and circuits for reliably and safely backing up selected data during the operation of a Fibre Channel switch, or the like.
2. Relevant Background
Mainframes, supercomputers, mass storage systems, workstations and very high-resolution display subsystems are frequently connected together to facilitate file and print sharing. Common networks and channels used for these types of connections oftentimes introduce communications bottlenecking, especially in cases where the data is in a large file format typical of graphically-based applications.
There are two basic types of data communications connections between processors and between a processor and peripherals: channels and networks. A “channel” provides a direct or switched point-to-point connection between communicating devices. The primary task of a channel is to transport data at the highest possible data rate with the least amount of delay. Channels typically perform simple error correction in hardware. A “network”, by contrast, is an aggregation of distributed nodes (e.g. workstations, mass storage units) with its own protocol, which supports interaction among these nodes. Typically, each node contends for the transmission medium, and each node must be capable of recognizing error conditions on the network and must provide the error management required to recover from the error conditions.
One type of communications interconnect that has been developed is Fibre Channel. The Fibre Channel protocol was developed and adopted as the American Nation Standard for Information Systems (ANSI). See Fibre Channel Physical and Signaling Interface, Revision 4 2, American National Standard for Information Systems (ANSI) (1993) for a detailed discussion of the Fibre Channel standard. Briefly, Fibre Channel is a switched protocol that allows concurrent communication among workstations, supercomputers, and various peripherals. The total network bandwidth provided by Fibre Channel is on the order of tens or hundreds of gigabits per second. Fibre Channel is capable of transmitting frames at rates exceeding 1 gigabit per second simultaneously in both directions. It is also able to transport commands and data according to existing protocols such as Internet protocol (IP), small computer system interface (SCSI), high performance parallel interface (HIPPI), and intelligent peripheral interface (IPI) over optical fiber or copper cable.
FIG. 1
illustrates a variable-length frame
11
, as described by the Fibre Channel standard. The variable-length frame
11
comprises a 4-byte start-of-frame (SOF) indicator
12
, which is a particular binary sequence indicative of the beginning of the frame
11
. The SOF indicator
12
is followed by a 24-byte header, which generally specifies, among other things, the frame source address, the destination address, as well as whether the frame
11
is either control information or actual data.
The header
14
is followed by a field
16
of variable-length data. The length of the data frame
16
is 2112 bytes. The data
16
is followed successively by a 4-byte CRC (cyclical redundancy check) code
17
for error detection, and by a 4-byte end-of-frame (EOF) indicator
18
. The frame
11
of
FIG. 1
is much more flexible than a fixed frame, and provides for higher performance by accommodating the specific needs of specific applications.
FIG. 2
illustrates a block diagram of a representative Fibre Channel architecture in a Fibre Channel network
100
. As an example of the architecture, a workstation
120
, a mainframe
122
, and a supercomputer
124
are interconnected with various subsystems via a Fibre Channel fabric
110
(i.e., a Fibre Channel switch). The subsystems may include, for example, a tape subsystem
126
, a disk subsystem
128
, and a display subsystem
130
. The fabric
110
is an entity that interconnects various node-ports (N_ports)
140
and their associated workstations.
Mainframes and peripherals are attached to the fabric
110
through the fabric ports (F_ports)
142
. The essential function of the fabric
110
is to receive frames of data from a source N_port, and, using a first protocol, to route the frames to a destination N_port. In a preferred embodiment, the first protocol is the Fibre Channel protocol. Other protocols, such as the asynchronous transfer mode (ATM) also can be used.
Thus, the Fibre Channel is a channel-network hybrid, containing enough network features to provide the needed connectivity, distance, and protocol multiplexing, and enough channel features to retain simplicity, repeatable performance, and reliable delivery. The Fibre Channel
110
allows for an active, intelligent interconnection scheme, known as a “fabric,” or Fiber Channel switch, to connect devices. The fabric includes a plurality of (F_ports) that provide for interconnection and frame transfer between a plurality of (N_ports) attached to associated devices that may include workstations, supercomputers and/or peripherals. The fabric has the capability of routing frames based upon information contained within the frames. The N_ports manages the simple point-to-point connections between themselves and the fabric. The type of N_ports and their associated devices dictates the rate that the N_ports transmit and receive data to and from the fabric. Transmission is isolated from the control protocol so that different topologies, such as point-to-point links, rings, multidrop buses, cross point switches, and the like, can be implemented.
The Fibre Channel industry standard also provides for several different types of data transfers. A class 1 transfer requires circuit switching, that is, a reserved data path through the network switch. Class 1 transfers generally involve the transfer of more than one frame, oftentimes numerous frames, between two identified network elements. In contrast, a class 2 transfer requires an allocation of a path through the network switch for each transfer of a single frame from one network element to another. Frame switching for class 2 transfers is more difficult to implement than class 1 circuit switching, as frame switching requires a memory mechanism for temporarily storing incoming frames in a source queue prior to their routing to a destination port, or a destination queue at a destination port. A memory mechanism typically includes numerous input/output (I/O) connections with associated support circuitry and queuing logic.
Additional complexity and hardware is required when channels carrying data at different bit rates are to be interfaced.
It is known to employ centralized queuing that is inherently slow, as a common block of logic must be employed, for all routing decisions within the switch. It is also known to employ distributed source queuing and distributed destination queuing.
In the past, mirroring operations have been employed to replicate data traversing a Fibre Channel switch. However, such multicast operations generally place the frame replicator directly in the path of the data, so that when a backup occurs, if a write is detected in the data to be backed up, the backup is put on hold until the write is completed.
SUMMARY OF THE INVENTION
In light of the above, therefore, it is an object of the invention to provide an improved method and circuit for use in backing up data frames in conjunction with a Fibre Channel switch.
To perform the data backup, a volume of data is replicated from a storage device using a reliable multicast protocol provided by a switched Fibre Channel storage area network. The majority of the replication takes place while an application continues to operate on the volume. While copying the data from
Grant Robert
Trevitt Stephen
Hogan & Hartson L.L.P.
Kim Hong
McData Corporation
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