JP4499909B2 - Multiplexed storage controller - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multiplexed storage control device connected between a host computer and a plurality of external storage devices.
[0002]
[Prior art]
In a computer system, a magnetic disk device (hereinafter referred to as HDD) is used as an external storage device. Conventionally, in order to cope with a failure of the HDD, data is multiplexed using a plurality of HDDs. A multiplexed storage control device that protects data by copying data from another HDD even when one HDD fails is employed.
[0003]
In such a multiplexed storage control device, when one HDD fails, the failed HDD is replaced with a new HDD, and data is restored to the original state by copying data from the other HDD to the replaced HDD. It is like that. Further, after the replacement, the HDD connection confirmation operation is performed.
[0004]
Such copying between HDDs and HDD connection confirmation operations are independent of the control of the host computer by the multiplexed storage control device when the HDD is not accessed from the host computer. To do it.
[0005]
Therefore, it is necessary for the multiplexed storage control device to determine whether or not the HDD is executing a command issued from the host computer, and when not being executed, it is necessary to perform a data copy between the HDDs and an HDD connection check operation. is there.
[0006]
In order to determine whether the HDD is executing a command issued from the host computer, conventionally, as shown in FIG. 10, the multiplexed storage control device 1 is connected to the host computer 2 and the first and second 2s. In a computer system connected between two HDDs 3 and 4, the multiplexed storage control device 1 is provided with a large-capacity buffer 5 for data transfer and a copy processing unit 6. When a command is issued, the issued write command and data to be written to the HDDs 3 and 4 are temporarily stored in the data transfer buffer 5.
[0007]
Whether or not the HDD is executing a command issued by the host computer 2 is determined by searching the buffer 5 and determining that the HDD is not executing the command if there is no data. It was supposed to copy data between.
[0008]
[Problems to be solved by the invention]
However, in such a multiplexed storage control device 1, in order to determine whether or not the host computer 2 issues a command to the HDD, a large-capacity buffer 5 for data transfer is required in the device. In addition, there is a problem that the cost becomes high.
[0009]
Therefore, the present invention can determine whether or not the host computer issues a command to the external storage device without using the data transfer buffer, and therefore can eliminate the need for the data transfer buffer. Provided is a multiplexed storage control device that can realize cost reduction.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a multiplexed storage control device connected between a host computer and a plurality of external storage devices. Ho Strike computer bus Close to A monitoring unit that monitors whether a signal supplied to the bus is active, an access unit that accesses the external storage device if the signal supplied to the bus is not active for a certain period of time, A storage unit for storing active states of a plurality of signals necessary for accessing an external storage device in advance; A command flag storage unit for storing a flag indicating a state waiting for a command issued from the host computer; The monitoring section Is Compares the active state of the signal stored in the storage unit with the state of the signal supplied to the bus to determine whether the signal necessary for accessing the external storage device supplied from the host computer to the bus is in the active state. Monitoring When the signal supplied to the bus is detected to be in an active state, it outputs a detection signal to the access unit, and the access unit that has received the detection signal sets a flag in the command flag storage unit, and the host computer Will not access the external storage device until the flag is reset Is.
[0014]
Claim 2 The described invention is claimed. 1 In the described multiplex storage control device, the access unit performs read access to one external storage device and write access to the remaining external storage devices.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing the configuration of a computer system using a multiplexed storage control device 11 of the present invention. The multiplexed storage control device 11 includes a host computer 12 and two first and second external storage devices. The HDDs 13 and 14 are connected.
[0018]
The multiplexed storage control device 11 includes a bus switching unit 15, an external storage device access unit 16, an access monitoring unit 17, and three interfaces (I / F) 18, 19, 20, and the interface 18 includes the host computer 12. , The first HDD 13 is connected to the interface 19, and the second HDD 14 is connected to the interface 20.
[0019]
The bus switching unit 15 switches and controls the bus between the host computer 12 and the HDDs 13 and 14, and the external storage device access unit 16 controls access to the HDDs 13 and 14, and the access monitoring unit 17 Determines whether or not the host computer 12 and the HDDs 13 and 14 are accessing. Each of the interfaces 18, 19, and 20 conforms to the ATA standard.
[0020]
The access monitoring unit 17 includes an access control unit 21, a counter unit 22, and a counter upper limit setting unit 23 as shown in FIG. The access monitoring unit 17 is connected to a write line, a read line, and a DMACK line, which are signal lines in the bus from the host computer 12. The access monitoring unit 17 is connected to an interrupt line, a DASP line, and a DMARQ line, which are signal lines in the bus from the HDDs 13 and 14.
[0021]
The access control unit 21 is provided with a storage unit 211 that stores the active state, that is, the high level or the low level, for each connected signal line.
[0022]
The access control unit 21 monitors each signal line from the host computer 12 and each signal line from the HDDs 13, 14, determines whether or not each signal line is activated, and the counter unit 22. Is counted by a signal from the access control unit 21, and when the count value reaches the upper limit value preset in the counter upper limit setting unit 23, the signal A is supplied to the external storage device access unit 16. Yes.
[0023]
That is, as shown in FIG. 3, the access monitoring unit 17 monitors whether or not all signal lines connected by the access control unit 21 are inactive for 100 ms in S1, and becomes active during that time. When it is determined that the counter has been reached, the counter unit 22 is cleared in S2.
[0024]
If all the signal lines are not active for 100 ms, a notification is sent to the counter unit 22 in S3, whereby the counter unit 22 counts up by one. In S4, it is determined whether or not the count value of the counter unit 22 has reached the upper limit value set in the counter upper limit setting unit 23. If the upper limit value has not been reached, the process returns to S1.
[0025]
If the count value of the counter unit 22 reaches the upper limit value set in the counter upper limit setting unit 23, the counter unit 22 is cleared and the signal A is output to the external storage device access unit 16 in S5. To do. As a result, the copy execution unit of the external storage device access unit 16 accesses the first and second HDDs 13 and 14 to start the copy operation.
[0026]
FIG. 4 shows that when the ATA HDD is used, the host computer 12 issues a read command for performing data transfer (PIO transfer) to the HDDs 13 and 14 without using the DMACK line and the DMARQ line, and the data transfer. 2 shows an example of the signal operation of each line connected to the access monitoring unit 17 until the start of.
[0027]
It should be noted that other lines are required to actually issue commands to the HDDs 13 and 14 from the host computer 12 and transfer data, but signals frequently used between the host computer 12 and the HDDs 13 and 14 are supplied. The signal lines to be used are listed.
[0028]
In the present embodiment, a write line and a read line, which are signal lines for frequently used write signals and read signals, are handled as signals necessary for accessing the HDDs 13 and 14 from the host computer 12. In addition, frequently used interrupt signals, interrupt lines that are signal lines of DASP signals, and DASP lines are handled as signals necessary for responses from the HDDs 13 and 14 to the host computer 12 for access from the host computer 12. The DASP line is a signal indicating that the HDDs 13 and 14 are currently being executed.
[0029]
Here, a write signal transmitted from the host computer 12 to the HDDs 13 and 14, a write line and a read line that are signal lines for read signals, an interrupt signal that is transmitted from the HDDs 13 and 14 to the host computer 12, and an interrupt that is a signal line for DASP signals. The case of a line and a DASP line will be described.
[0030]
The interrupt line is set to be active at a high level, and the write line, read line, and DASP line are set to be active at a low level. The storage unit 211 in the access monitoring unit 17 stores the signal line for each signal line. The active state of is stored. Then, the access monitoring unit 17 compares the active state of each signal line with the active state for each signal line stored in the storage unit 211 in the access control unit 21, so that the interrupt line is at a high level. When the write line, read line, and DASP line go low, it is determined to be active.
[0031]
Section a shows a section from when the host computer 12 confirms whether the command can be issued to when the command is issued, and a read signal is output from the host computer 12 to the lead wire. When the line goes low, it is determined to be active. Here, if the HDD 13 or the HDD 14 responds that the command cannot be issued, the host computer 12 waits until the command can be issued.
[0032]
A section b indicates a section in which a command is written. When the HDD 13 or the HDD 14 responds that the command can be issued, a write signal is output from the host computer 12 to the write line and the command is written. . At this time, since the write line is at a low level, it is determined to be active.
[0033]
A section c indicates a section from when the writing of the command to the disk of the HDD is completed until the HDD generates an interrupt. During this period, the signal from the host computer 12 to the HDD does not become active, but the DASP line becomes low level in response to the HDD, so it is determined to be active.
[0034]
A section d indicates a section from the occurrence of an interrupt to the start of data transfer, and the interrupt line to which the interrupt signal from the HDD is supplied is at a high level and is determined to be active. Further, since the DASP line is also kept at the low level, it is determined that this is also active.
[0035]
A section e indicates a section in which a read signal for data transfer is output from the host computer 12, and it is determined that the lead wire is at a low level and is active. Further, since the DASP line is also kept at the low level, it is determined that this is also active.
[0036]
The access monitoring unit 17 determines whether the write line and the read line are active as a signal from the host computer 12 to the HDD 13 or the HDD 14. Alternatively, it is determined whether the interrupt line and the DASP line are active as a signal from the HDD 13 or the HDD 14 to the host computer 12. Alternatively, it is determined whether or not all of the write line, read line, interrupt line, and DASP line are active.
[0037]
By such determination, it can be recognized that the HDD is being accessed by the host computer 12 until the command is issued from the host computer 12 and the command processing is completed.
[0038]
When the access monitoring unit 17 determines whether or not only the write line and the read line are active, since it cannot be recognized during the section c, the counter upper limit setting unit 23 is set in this case. It is necessary to set the upper limit value, that is, the monitoring time to a time longer than the time of the section c.
[0039]
Further, when the access monitoring unit 17 determines whether or not only the interrupt line and the DASP line are active, it cannot recognize between the section a and the section b. In this case, the counter upper limit setting is performed. The upper limit value set in the unit 23, that is, the monitoring time needs to be set to a time longer than the time obtained by adding the time of the section a and the time of the section b.
[0040]
When the access monitoring unit 17 determines whether or not all of the write line, read line, interrupt line, and DASP line are active, an upper limit value set in the counter upper limit setting unit 23, That is, the monitoring time can be shortened compared to the case of only the write line, read line, interrupt line, and DASP line.
[0041]
FIG. 5 shows that when the ATA HDD is used, the host computer 12 issues a read command for performing data transfer (DMA transfer) to the HDDs 13 and 14 using the DMACK line and the DMARQ line to transfer the data. An example of the signal operation of each line connected to the access monitoring unit 17 until the start is shown.
[0042]
It should be noted that other lines are required to actually issue commands to the HDDs 13 and 14 from the host computer 12 and transfer data, but signals frequently used between the host computer 12 and the HDDs 13 and 14 are supplied. The signal lines to be used are listed. In the present embodiment, as signals necessary for accessing the HDDs 13 and 14 from the host computer 12, frequently used write signals, read signal signal lines and read lines, and DMARQ signal signal lines DMARQ. Handle lines. In addition, as signals necessary for a response from the HDDs 13 and 14 to the host computer 12 in response to an access from the host computer 12, an interrupt signal that is frequently used, an interrupt line that is a signal line of the DASP signal, a DASP line, and a DMACK signal The DMACK line, which is a signal line, is handled. The DMARQ line is a signal line for the host computer 12 notifying the HDDs 13 and 14 that preparation for data transfer has been completed. The DMACK line is a signal line for notifying that the HDDs 13 and 14 can transfer data to the host computer 12.
[0043]
The interrupt line and DMARQ line are set to be active at a high level, and the write line, read line, DASP line, and DMACK line are set to be active at a low level. The storage unit 211 in the access control unit 21 stores The active state is stored for each signal line. The access monitoring unit 17 compares the active state of each signal line with the active state of each signal line stored in the storage unit 211 in the access control unit 21 to obtain an interrupt line, a DMARQ line, Is active, when the high level, the write line, the read line, the DASP line, and the DMACK line become low level.
[0044]
Section a shows a section from when the host computer 12 confirms whether the command can be issued to when the command is issued, and a read signal is output from the host computer 12 to the lead wire. When the line goes low, it is determined to be active. Here, if the HDD 13 or the HDD 14 responds that the command cannot be issued, the host computer 12 waits until the command can be issued.
[0045]
A section b indicates a section in which a command is written. A write signal is output from the host computer 12 to the write line, and the command is written. At this time, since the write line is at a low level, it is determined to be active.
[0046]
A section c indicates a section from when the writing of the command to the disk of the HDD is completed until the HDD generates an interrupt. During this period, the signal from the host computer 12 to the HDD does not become active, but the DASP line becomes low level in response to the HDD, so it is determined to be active.
[0047]
An interval d indicates an interval from the occurrence of an interrupt to the start of data transfer. The DMARQ line that supplies a signal for requesting data transfer becomes high level and is determined to be active. Further, since the DASP line is also kept at the low level, it is determined that this is also active.
[0048]
A section e indicates a section in which a read signal for data transfer is output from the host computer 12, and it is determined that the lead wire is at a low level and is active. Further, since the DASP line is also kept at the low level, it is determined that this is also active. Also, since the DMARQ line remains at the high level, it is determined that this is also active. Further, the DMACK line that supplies a response signal that permits a data transfer request goes low, and it is determined that this is also active.
[0049]
The access monitoring unit 17 determines whether a write line, a read line, and a DMACK line are active as a signal from the host computer 12 to the HDD 13 or the HDD 14. Alternatively, it is determined whether an interrupt line, a DASP line, or a DMARQ line is active as a signal from the HDD 13 or the HDD 14 to the host computer 12. Alternatively, it is determined whether or not all of the write line, read line, DMACK line, interrupt line, DASP line, and DMARQ line are active.
[0050]
By such determination, it can be recognized that the HDD is being accessed by the host computer 12 until the command is issued from the host computer 12 and the command processing is completed.
[0051]
When the access monitoring unit 17 determines whether or not only the write line, the read line, and the DMACK line are active, it cannot recognize the interval c and the interval d. In this case, the upper limit of the counter The upper limit value set in the setting unit 23, that is, the monitoring time needs to be set to a time longer than the time obtained by adding the time of the section c and the time of the section d.
[0052]
Further, when the access monitoring unit 17 determines whether or not only the interrupt line, the DASP line, and the DMARQ line are active, it cannot recognize between the section a and the section b. The upper limit value set in the counter upper limit setting unit 23, that is, the monitoring time needs to be set to a time longer than the time obtained by adding the time of the section a and the time of the section b.
[0053]
When the access monitoring unit 17 determines whether or not all of the write line, read line, DMACK line, interrupt line, DASP line, and DMARQ line are active, the counter upper limit setting unit 23 Can be shortened compared to the case of only the write line, read line, DMACK line, interrupt line, DASP line, and DMARQ line.
[0054]
The external storage device access unit 16 accesses the HDD 13 or 14 to confirm the connection when performing the connection confirmation operation of the HDD 13 or 14. Access at this time is performed by writing a certain value with a write command and reading the written value with a read command.
[0055]
In such a configuration, for example, when the access monitoring unit 17 determines whether only the write line, the read line, or the DMACK line is active, any one of the write line, the read line, and the DMACK line is determined. When it becomes active, an active determination is made and the counter unit 22 is cleared.
[0056]
Further, if neither line is active for 100 ms, 1 is added to the counter unit 22, and the counter unit 22 counts up if it remains inactive. When the count value of the counter unit 22 reaches the upper limit value set in the counter upper limit value setting unit 23, the signal A is supplied from the counter unit 22 to the external storage device access unit 16.
[0057]
When the external storage device access unit 16 receives the signal A, the external storage device access unit 16 accesses the HDDs 13 and 14 to start copying and connection confirmation operations.
[0058]
For example, when the access monitoring unit 17 determines whether only the interrupt line, the DASP line, or the DMARQ line is active, the active determination is made when any of the interrupt line, the DASP line, or the DMARQ line becomes active. To clear the counter unit 22.
[0059]
Further, if neither line is active for 100 ms, 1 is added to the counter unit 22, and the counter unit 22 counts up if it remains inactive. When the count value of the counter unit 22 reaches the upper limit value set in the counter upper limit value setting unit 23, the signal A is supplied from the counter unit 22 to the external storage device access unit 16.
[0060]
When the external storage device access unit 16 receives the signal A, the external storage device access unit 16 accesses the HDDs 13 and 14 to start copying and connection confirmation operations.
[0061]
For example, when the access monitoring unit 17 determines whether or not all of the write line, read line, DMACK line, interrupt line, DASP line, and DMARQ line are active, the write line, read line, When any of the DMACK line, the interrupt line, the DASP line, and the DMARQ line becomes active, an active determination is made and the counter unit 22 is cleared.
[0062]
Further, if neither line is active for 100 ms, 1 is added to the counter unit 22, and the counter unit 22 counts up if it remains inactive. When the count value of the counter unit 22 reaches the upper limit value set in the counter upper limit value setting unit 23, the signal A is supplied from the counter unit 22 to the external storage device access unit 16.
[0063]
When the external storage device access unit 16 receives the signal A, the external storage device access unit 16 accesses the HDDs 13 and 14 to start copying and connection confirmation operations.
[0064]
In this way, it is possible to determine whether or not the host computer 12 has issued a command to the HDD without using a large-capacity buffer for data transfer in the multiplexed storage control device 11, and accordingly, a buffer for data transfer. Can be eliminated, and the cost can be reduced.
[0065]
When the access monitoring unit 17 determines whether or not all of the write line, read line, DMACK line, interrupt line, DASP line, and DMARQ line are active, the write line, read line, DMACK line As compared with the case where it is determined whether only the interrupt line, the DASP line and the DMARQ line are active or not, the host computer 12 is not accessing the HDD. Therefore, operations such as HDD copying and HDD connection confirmation can be started quickly.
[0066]
When the access monitoring unit 17 determines whether or not only the write line, the read line, or only the write line, the read line, or the DMACK line is active, the interrupt line, DASP line, The DMARQ line may not be connected to the access control unit 21. When the access monitoring unit 17 determines whether only the interrupt line, DASP line, or only the interrupt line, DASP line, and DMARQ line are active, the write line, read line, DMACK from the host computer 12 is used. The line may not be connected to the access control unit 21.
[0067]
(Second Embodiment)
In addition, the same code | symbol is attached | subjected to the part same as embodiment mentioned above, and detailed description is abbreviate | omitted.
FIG. 6 is a block diagram showing the configuration of a computer system using the multiplexed storage control device 11 of the present invention. The multiplexed storage control device 11 is a host computer 12 and first and second two units which are external storage devices. The HDDs 13 and 14 are connected.
[0068]
The multiplexed storage control device 11 includes a bus switching unit 151, an external storage device access unit 161, an access monitoring unit 171, and three interfaces (I / F) 18, 19, and 20. The interface 18 includes the host computer 12. , The first HDD 13 is connected to the interface 19, and the second HDD 14 is connected to the interface 20.
[0069]
The bus switching unit 151 includes a detection unit 31 and controls switching of the bus between the host computer 12 and the HDDs 13 and 14, and when a command is issued from the host computer 12 to the HDD 13 or 14. The detection unit 31 detects this and outputs a signal C to the external storage device access unit 161.
[0070]
As shown in FIG. 7, the access monitoring unit 17 includes an access control unit 21, a counter unit 22, a counter upper limit setting unit 23, and a read / write monitoring unit 24, and the read / write monitoring unit 24 includes the host computer 12. The write line and the read line are connected, and when either the write line or the read line becomes active, it is determined that the signal R is output to the external storage device access unit 161.
[0071]
As shown in FIG. 8, the external storage device access unit 161 includes an access recognition unit 41, a command flag storage unit 42 that stores a flag indicating a state of waiting for command issuance, and whether or not to start copying. A copy start flag storage unit 43 that stores a flag, a command reception unit 44, a read / write recognition unit 45, and a copy execution unit 46 are provided.
[0072]
The access recognition unit 41 performs control to change the flag of the command flag storage unit 42 and the flag of the copy start flag storage unit 43 from the signal A from the access monitoring unit 171 and the flag content of the command flag storage unit 42. To do.
[0073]
The command receiving unit 44 receives the signal C from the bus switching unit 151 and changes the flag in the command flag storage unit 42. The read / write recognition unit 45 performs control to change the flag of the command flag storage unit 42 based on the signal R from the access monitoring unit 171 and the flag content of the command flag storage unit 42. The copy execution unit 46 accesses the HDDs 13 and 14 to execute copy.
[0074]
In the external storage device access unit 161, if there is an access from the host computer 12 while the copy execution unit 46 is copying, a signal R is output from the access monitoring unit 171. In response to this signal R, the command flag is set in the command flag storage unit 42 and the copy start flag in the copy start flag storage unit 43 is cleared. When the copy start flag in the copy start flag storage unit 43 is cleared, the copy execution unit 46 interrupts copying.
[0075]
Thereafter, when the access monitoring unit 171 determines that the counter unit 22 has not accessed the host computer 12 and the HDD for a certain period of time and outputs a signal A, as shown in FIG. The unit 41 inputs the signal A, and in S12, the access recognition unit 41 determines whether or not the command flag is set in the command flag storage unit 42. Since the command flag is set in the command flag storage unit 42 now, the command flag storage unit 43 does not set the copy start flag.
[0076]
Next, when a command is issued from the host computer 12, the detection unit 31 of the bus switching unit 151 detects it and outputs a signal C to the external storage device access unit 161. As a result, the command reception unit 44 of the external storage device access unit 161 is notified that the command has been issued from the host computer 12.
[0077]
When the command reception unit 44 is notified that the host computer 12 has issued a command, the command reception unit 44 clears the command flag in the command flag storage unit 42.
[0078]
Thereafter, when the access monitoring unit 171 determines that the counter unit 22 has not accessed the host computer 12 and the HDD for a certain period of time and outputs a signal A, as shown in FIG. The unit 41 inputs the signal A, and in S12, the access recognition unit 41 determines whether or not the command flag is set in the command flag storage unit 42. This time, since the command flag is not set in the command flag storage unit 42, the access recognition unit 41 sets the copy start flag in the copy start flag storage unit 43 in S13.
[0079]
When the copy start flag is set in the copy start flag storage unit 43, the copy execution unit 46 resumes copying.
[0080]
Normally, the host computer 12 issues a command immediately after confirming whether a command can be issued to the HDD. However, there is a case where the command cannot be issued immediately after checking whether or not the command can be issued to the HDD in various processing steps of the host computer 12.
[0081]
In such a case, since the command flag is set in the command flag storage unit 42 until the command is issued from the host computer 12, the copying is not resumed. That is, even when a command is not issued immediately from the host computer 12, copying can be suspended until a command is issued. Whether the command processing is completed after the command is issued is monitored by the counter unit 22 of the access monitoring unit 171. When the command processing is completed, copying can be resumed.
[0082]
In this embodiment as well, as in the first embodiment described above, the host computer 12 issues a command to the HDD without using a large-capacity buffer for data transfer in the multiplexed storage controller 11. Therefore, the data transfer buffer can be made unnecessary, and the cost can be reduced.
[0083]
In this embodiment, the access recognition unit 41 determines whether or not the command flag is set in the command flag storage unit 42 and determines whether or not to set the copy start flag in the copy start flag storage unit 43. However, the present invention is not necessarily limited to this. A counter is provided in the access recognition unit, and a copy start flag is set in the copy start flag storage unit 43 when a command is not issued for a certain period of time. Good. In this way, copying can be resumed even if a command is not issued after access from the host computer 12.
[0084]
In the above-described embodiments, the case where two HDDs are used as the external storage device has been described. However, the present invention is not limited to this, and three or more HDDs may be used. Further, an external storage device other than the HDD may be used.
[0085]
【The invention's effect】
According to the invention described in each claim, it is possible to determine whether or not the host computer issues a command to the external storage device without using the data transfer buffer, so that the data transfer buffer is unnecessary. And cost reduction. According to the fourth aspect of the present invention, the command is issued even if the host computer does not issue the command immediately after checking whether the command can be issued to the external storage device. The access to the external storage device can be interrupted until it is done.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a computer system using a multiplexed storage control device according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an access monitoring unit in the embodiment.
FIG. 3 is a flowchart showing an operation of an access monitoring unit in the embodiment.
FIG. 4 is a timing chart showing an example of the signal operation of each line connected to the access monitoring unit in the embodiment.
FIG. 5 is a timing chart showing another example of the signal operation of each line connected to the access monitoring unit in the embodiment.
FIG. 6 is a block diagram showing a configuration of a computer system using a multiplexed storage control device according to a second embodiment of the present invention.
FIG. 7 is an exemplary block diagram showing a configuration of an access monitoring unit according to the embodiment;
FIG. 8 is an exemplary block diagram showing the configuration of an external storage device access unit according to the embodiment;
FIG. 9 is a flowchart showing processing of an access recognition unit in the embodiment.
FIG. 10 is a block diagram showing a conventional example.
[Explanation of symbols]
11: Multiplexed storage device
12 ... Host computer
13, 14 ... Magnetic disk drive (HDD)
16 ... External storage device access unit
17 ... Access monitoring unit

Claims (2)

In a multiplexed storage control device connected between a host computer and a plurality of external storage devices,
Is connected to the bus before Symbol host computer, and a monitoring unit signal supplied to the bus to monitor whether the active state,
An access unit for accessing the external storage device if the signal supplied to the bus is not active for a certain period of time;
A storage unit for storing active states of a plurality of signals necessary for accessing an external storage device in advance ;
A command flag storage unit for storing a flag indicating a state of waiting for a command issued from the host computer ;
The monitoring unit of the previous SL by comparing the state of the signal supplied to the active state and bus signal stored in the storage unit, signals required from the host computer to access the external storage device is supplied to the bus When the signal supplied to the bus is detected to be in an active state, a detection signal is output to the access unit,
The access unit that has received the detection signal sets the flag in the command flag storage unit and does not access the external storage device until a command is issued from the host computer and the flag is reset. A multiplexed storage control device. 2. The multiplexed storage control device according to claim 1 , wherein the access unit performs read access to one external storage device and performs write access to the remaining external storage devices.

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