JPH05173943A - Bus switching device and computer device including this device - Google Patents

Abstract

PURPOSE:To constitute the system which has a relatively simple and inexpensive computer fault resistance performance. CONSTITUTION:In a bus switching device 30 which connects two computers and two magnetic disk devices, first and second switches 24A and 24B to connect a first SCSI bus 20A, a second SCSI bus 20B, and a third SCSI bus 22Y having single initiator specifications are switched by a switching means 26 to connect one side which first requests connection. Since switches 24A and 24B can be simultaneously turned off but are not simultaneously turned on, collision between signals of buses 20A and 20B is eliminated. The first and/or second switch is released to release monopolization of the bus if the time when the bus is monopolized and no signals are communicated exceeds a prescribed time T.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bus switching device and a computer device including the bus switching device, and more particularly, it has a fault tolerance when a group of external storage devices are accessed by a plurality of computers through a SCSI bus. Designed to
The present invention relates to a computer device including a bus switching device and a bus switching device for connecting a plurality of computers each having a bus interface board of a single initiator specification, which is suitable for configuration, and an external peripheral device.

[0002]

2. Description of the Related Art In a computer system, a system having fault tolerance (hereinafter referred to as fault tolerance system)
Is generally incorporated as a high-end system,
For example, it is designed and configured as shown in FIG.

The fault-tolerant system shown in FIG. 6 has two computers A and B, and an external storage device is provided between these computers. This external storage device is, for example, a magnetic disk device (HDD1, HDD
2) is used. Also, these magnetic disk devices HDD
The 1 and the HDD 2 constitute a so-called mirror disk to which the same data is input and output.

Computers A and B input / output data to / from the magnetic disk devices HDD1 and HDD2 via a first SCSI bus 1 and a second SCSI bus 2. Therefore, each computer A and B is connected to each SCSI bus 1
And SCS for connecting the bus in the computer to 2
It is provided with I boards A1, A2 and B1, B2. Each of these SCSI boards A1, A2 and B1, B2 is a multi-initiator (it can be supported even if there are two or more instructions)
Must be spec. That is, these computers A
And SCSI boards A1, A2 and B of computer B
Since 1 and B2 are connected to the same SCSI buses 1 and 2, respectively, the SCSI board needs to have a multi-initiator specification.

The computers A and B have CPU boards 10A and 10B, various boards 12A and 12B, and various buses 14A and 14B therein. Further, the computer A is a main operation computer and the computer B is an auxiliary operation computer.
Further, it is assumed that the failure in the computer system occurs at only one place at a time.

The fault-tolerant system shown in FIG. 6 has fault tolerance for the SCSI bus with respect to each of the following faults (1) to (4).

(1) CPU board 10 of computer A
If A fails, the computer B uses the SCSI boards B1 and B2 to access the magnetic disk devices HDD1 and HD.
It is possible to access the data of D2.

(2) SCSI board A of computer A
If one fails but does not occupy the first SCSI bus 1, the computer A can access the data of the magnetic disk device HDD2 through the SCSI board A2. In addition, the computer B passes the SCSI boards B1 and B2 to the magnetic disk devices HDD1 and HD.
It is possible to access the data of D2.

(3) SCSI board A of computer A
If 1 fails and remains occupying the first SCSI bus 1, the magnetic disk device HDD 1 cannot access. Further, the computers A and B can access the data of the magnetic disk device HDD2 through the SCSI boards A2 and B2.

(4) When the magnetic disk device HDD1 fails, the computers A and B are replaced by SCSI boards A2 and B.
It is possible to access the magnetic disk device HDD2 through the HDD2.

[0011]

However, the fault-tolerant system for a computer as described above has the following problems.

That is, each SCSI of each computer A, B
Boards A1, A2, B1 and B2 are connected for the same SCSI buses 1 and 2, so each SCSI board A1, A2
2, B1 and B2 need to be multi-initiator specifications. This multi-initiator specification is more complicated in software and hardware than the single-initiator (only one instruction side can be supported) specification.

When the SCSI board fails while keeping the SCSI bus occupied, the dedicated SCS
Since the I-bus cannot be used, the number of SCSI buses corresponding to the number of SCSI buses is used for designing and configuring a fault-tolerant system.
Need a board. For example, in the system shown in FIG.
Each computer has two SCSI boards (SC
Two SI boards A1 and A2 and a SCSI board B1
And B2 each), which is expensive.

Therefore, there has been a problem that it becomes an obstacle when a system having a fault tolerance performance (fault tolerance system) is constructed with an inexpensive personal computer.

The present invention has been made to solve the above-mentioned conventional problems, and a bus switching device and a bus capable of constructing a fault-tolerant performance system relatively easily and inexpensively using an inexpensive personal computer. An object is to provide a computer device including a switching device.

[0016]

According to the present invention, there are provided a bus switching device for connecting a plurality of computers having a bus interface board of a single initiator specification and an external peripheral device, and a bus from each computer, By providing the connecting means for connecting the bus from the external peripheral device and the switching means for switching the connection state of the connecting means so as to connect the one having the connection request first, It solves the problem.

Further, the present invention may further comprise a time-out detecting means for releasing the bus when the bus is occupied and the time during which no signal is communicated exceeds a predetermined time.

Further, the present invention is to solve the above problems by including the bus switching device in a computer device including the bus switching device.

[0019]

In order to construct a system having fault tolerance relatively easily and inexpensively when the peripheral device, for example, a group of external storage devices is accessed by a plurality of computers via the bus interface, the inventor has various advantages. The present invention was devised through examination.

In this case, the fault-tolerant system is constructed by using a computer having a single-initiator specification bus interface board, for example, a personal computer. Further, the buses of the respective bus interface boards are treated as separate buses, and any one of the buses is connected to an external peripheral device by a connecting means. In addition, if any bus interface board fails, the bus of the computer and external peripheral devices are The connection means between the buses can be opened.

Next, the operation of the present invention will be described based on the configuration example of the bus switching device according to the present invention shown in FIG.

In the bus switching device 30 of FIG. 1, a SCSI bus interface board is illustrated as the bus interface board. However, this bus is not limited to the SCSI bus interface board, and the present invention can be applied to a computer having a bus of various other standards as long as it is a bus interface board of a single initiator specification. is there.

In FIG. 1, the first SCSI bus 20A
And the interface board of each computer connected to the second SCSI bus 20B is a single-initiator type, and is an ANSI X3T9,2 REV. It is limited to 17B and operates without an arbitration phase (when multiple requests overlap, the request is determined as one of the requests) and without a reselection phase (when the target side selects a host).

Similarly, the target (external peripheral device, for example, a magnetic disk device HDD of an external storage device) connected to the third SCSI bus 22Y is the same as the ANSI X3T.
9.2 REV. 17B, and operate.

The overall connection relationship between the bus switching device 30 of FIG. 1 and the computers A and B and the magnetic disk device HDD is as shown in FIG.

As shown in FIG. 2, the first SCSI bus 2
A computer A that performs the main operation is connected to 0A.
A computer B that performs an auxiliary operation is connected to the second SCSI bus 20B. Also, the third SCSI bus 2
A group of external storage devices is connected to 2Y. Each bus 2
As shown in FIG. 1, respective bus interface boards 20a, 20b, 22y are provided at the input and output ends of the bus switching device 30 of 0A, 20B, 22Y.

As shown in FIG. 1, the first SCSI bus 20A and the third SCSI bus 2 which are actually used are used.
Between the 2Ys, the first SCSI bus 20A is connected to the third SC
First switch 24A for connecting to SI bus 22Y
Is provided. Also, the second SCSI bus 20B and the third
The second SCSI bus 20 is connected between the SCSI buses 22Y of
A second switch 24B is provided to connect B to the third SCSI bus 22Y.

The outputs of the switching means 26 for switching the connection state of the switches 24A and 24B are input to the respective switches 24A and 24B. The switching means 26 includes the switches 24A,
The connection state of 24B is connected first to the one having a connection request, and arbitration is performed for switching. The switching means 26 switches each of the switches 24A and 24B so that only one of them is turned on or both of them are turned off.

An algorithm for acquiring the bus by connecting the first and second SCSI buses 20A and 20B to the third SCSI bus 22Y by the switching means 26 will be described with reference to the time chart shown in FIG.

That is, as shown in FIG. 3, it is assumed that both the first and second switches 24A and 24B are initially off, that is, the third SCSI bus 22Y is unused.

Thereafter, the first and second SCSI buses 20
When a signal for selecting one of the buses A and 20B is input, the switching means 26 causes the first and second switches 2 to operate.
Turn on the switch of 4A and 24B, whichever changes earlier from "unused to used", and turn on the third SCSI
Connect to bus 22Y. That is, the bus selected by the bus selection signal acquires the third SCSI bus 22Y. In FIG. 3, at time t1, the first SCSI bus 2
Since the selection signal of 0A is input and the control signal of the first switch 24A is turned on, the first SCSI bus 20A acquires the third SCSI bus 22Y.

When either the first or second SCSI bus 20A or 20B is connected to the third SCSI bus 22Y, the bus selection signal of the one not connected becomes "unused → used". Even if it changes, the bus remains switched off. Therefore, the third SCSI bus 2
There is no response from 2Y, and acquisition of the third SCSI bus 22Y fails. For example, in FIG. 3, at time t2, the selection signal of the second SCSI bus 20B is “unused →
Change to "Use", but because the first SCSI bus 20A is already connected to the third SCSI bus 22Y,
The second SCSI bus 20B is the third SCSI bus 2 concerned.
Fail to get 2Y.

Since the first switch 24A and the second switch 24B are not turned on at the same time, the first S
The signals on the CSI bus 20A and the second SCSI bus 20B do not collide.

The connection between any one of the first and second SCSI buses 20A and 20B and the third SCSI bus 22Y continues until a series of SCSI bus data transfer is completed.

For example, the first SCSI bus 20A and the third SCSI bus 20A
The SCSI bus 22Y transfer continues until time t3 when the data transfer ends in FIG.

When a series of SCSI bus data transfer is completed, the bus selection signal of the third SCSI bus 22Y changes from "used to unused". At this time, therefore, the first and second SCSI buses connected to each other are connected. One of 20A and 20B becomes "used → not used", and one of the first and second switches 24A and 24B that has been turned on is turned off.

In this manner, when both switches are turned off, the next first and second SCSI buses 20
The bus selection signal of either A or 20B can be accepted. Therefore, as shown in FIG. 3, the second SCS
If the selection signal of the I-bus 20B changes to "unused → used" at time t4, the second switch is used as in the case of the first switch 24A.
The selection signal of the switch 24B is turned on, and the second bus 20B acquires the third bus 22Y.

As described above, the switching means 26 connects and arbitrates the access of the first and second buses 20A and 20B, whichever has the connection request first.

By inputting the compulsory switching signal to the switching means 26, the first and second switches 24A or 2
Either 4B can be forced on manually.

The system of FIG. 2 has the bus switching device 30.
Has the following fault tolerance performance.

In other words, when the computer A fails, the other computer B irrespective of whether it occupies the first SCSI bus 20A, the other computer B uses the magnetic disk device HDD1 or HDD
2 can be accessed separately from the computer A.

If the magnetic disk device HDD1 fails but does not occupy the third SCSI bus 22Y,
The computer A can access the HDD 2. As a result, the above-mentioned (1)
When the system having the fault-tolerant performance of (4) is connected to a plurality of computers having a single-initiator type bus interface board and an external peripheral device such as an external storage device, a bus from each of these computers is used. A connection means for connecting a bus from an external peripheral device and a switching means for switching the connection state of the connection means so that the one having a connection request first is connected can be provided. Therefore, a relatively inexpensive computer such as a personal computer can be used to construct a relatively simple and inexpensive system having fault tolerance performance.

Here, in the present invention, it is possible to provide means for releasing the bus when the bus is exclusively used and the time during which signals are not communicated exceeds a predetermined time. In the circuit of FIG. 1, the first and second SCS
Both the I buses 20A and 20B are provided with means (timeout detection means) 28A and 28B for releasing the bus. An algorithm for disconnecting the SCSI bus by the time-out detecting means 28A and 28B will be described with reference to the time chart of FIG.

FIG. 4 illustrates the first and second SCSI buses 20.
Bus selection signals of A and 20B, the buses 20A and 20
6 is a time chart of a B handshake signal, a timeout detection state, and control signals of the first and second switches 24A and 24B.

Now, it is assumed that one of the first and second SCSI buses 20A and 20B has acquired the third SCSI bus 22Y (after time t5 in FIG. 4).

In this case, the time-out detecting means 28A and 28B receive a handshake signal (a signal for timing data transfer) from either the first or second SCSI bus 20A or 20B that has acquired the third SCSI bus 22Y. ) Is entered.

When the signal of this handshake signal is fixed positively or negatively for a predetermined time T or longer, the timeout detection means 28A and 28B change from "undetected to detected",
A time-out detection command is output to the switching means 26. At this time, the switching means 26 has the first and second switches 24A that have been turned on in accordance with the time-out detection command.
And either 24B or 24B. This releases any of the buses 20A and 20B to which the third SCSI bus 22Y was connected. The time-out detection time can be set to about 100 msec (± 10 msec) when the external peripheral device is a magnetic disk device.

The time-out detecting means may be manually disabled.

With the above arrangement, the fault tolerance of the system can be further enhanced.

[0050]

Embodiments of the present invention will now be described in detail with reference to the drawings.

This embodiment is a computer device including a bus switching device embodying the present invention. As shown in FIG. 5, the computer device according to the embodiment includes computers A and B.
A bus switching device 30 and a group of magnetic disk devices HD
D, a terminal switching device 32, and a terminal 34.

The computer A is a computer that performs the main operation, and the SCSI bus operates as a single initiator. In addition, the computer A has a terminal port.

The computer B is a computer which performs an auxiliary operation, and operates as a single initiator of the SCSI bus. In addition, the computer B has the same terminal port as the computer A. or,
It operates when computer A stops, fails, or load balancing is desired.

The magnetic disk device HDD functions as a group of external storage devices.

Since the bus switching device 30 has the same structure as that shown in FIG. 1, the description thereof will be omitted.

The terminal switching device 32 connects the terminal 34 of an external input / output device (for example, screen output or keyboard input) to either the computer A or the computer B which is operating.

The terminal 34 is adapted to display operating computer information on a screen and output keyboard input information to either computer A or B.

In the apparatus of the embodiment shown in FIG. 5, all the data required by the computers A and B are stored in the magnetic disk drive HDD in order to provide fault tolerance.

Next, the operation of the embodiment will be described. When the computer A is processing a certain work (load), it is assumed that the computer A fails.

If the required data is stored in the magnetic disk device HDD, the bus switching device 30 will operate in the computer A.
Of the first SCSI bus 20A of the HDD
Can be disconnected from and connected to computer B. Then, the computer B can execute the work processed by the computer A on behalf of the computer A.

Therefore, the fault tolerance becomes high.

In the above embodiment, the case where the present invention is applied to the bus switching device that switches between two computers has been illustrated, but the scope of application of the present invention is not limited to this, and three or more computers. The bus switching device according to the present invention can be used for the bus switching.

Further, in the above-mentioned embodiment, the magnetic disk device is exemplified as the external peripheral device, but the external peripheral device is not limited to this magnetic disk device, and other kinds of external peripheral devices, for example, magnetic tapes. Recording device and RA
It is also applicable when using M (random access memory).

[0064]

As described above, according to the present invention, a relatively simple and inexpensive fault tolerant system is constructed by a plurality of computers having a single-initiator type bus interface, for example, personal computers. be able to. That is an excellent effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration example of a bus switching device according to the present invention for explaining the present invention.

FIG. 2 is likewise a block diagram showing a configuration example of a computer device including the bus switching device.

FIG. 3 is likewise a time chart for explaining the operation of the bus switching device.

FIG. 4 is a time chart for explaining the operation of a time-out detection means provided in the bus switching device.

FIG. 5 is a block diagram showing an overall configuration of a computer device including a bus switching device according to an embodiment of the present invention.

FIG. 6 is a block diagram showing an example of the overall configuration of a conventional system having fault tolerance.

[Explanation of symbols]

 1 ... 1st SCSI bus, 2 ... 2nd SCSI bus, 20A ... 1st SCSI bus, 20a ... 1st SCSI bus interface board, 20B ... 2nd SCSI bus, 20b ... 2nd SCSI bus Interface board, 22Y ... third SCSI bus, 20y ... third SCSI bus interface board, 24A ... first switch, 24B ... second switch, 26 ... switching means, 28A, 28B ... timeout detecting means, 30 ... Bus switching device, A, B ... Computer, HDD, HDD1, HDD2 ... Magnetic disk device.

Claims (3)

[Claims] 1. A bus switching device for connecting a plurality of computers having a single-initiator type bus interface board to an external peripheral device, wherein a bus from each computer and a bus from the external peripheral device are connected. A bus switching device, comprising: a connection means for connecting the connection means and a switching means for switching the connection state of the connection means so that the one having a connection request first is connected. 2. The method according to claim 1, further comprising a time-out detecting means for releasing the connecting means when the bus is occupied and the time during which signals are not communicated exceeds a predetermined time. Characteristic bus switching device. 3. A computer device including a bus switching device, comprising the bus switching device according to claim 1.