Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1999-08-17
2002-05-14
Verbrugge, Kevin (Department: 2185)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S118000
Reexamination Certificate
active
06389508
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information storing apparatus such as a magnetic disk drive or the like for writing data transferred by a write command from a host onto a medium. More particularly, the invention relates to an information storing apparatus for receiving data of write commands subsequent to a plurality of write command successively issued from a host during the writing of data onto a medium and processing it.
In an information storing apparatus known as a hard disk, when a host writes data onto the hard disk, the host issues a write command, the hard disk requests the host to generate data in response to the write command, stores the data into a data buffer, and writes the data onto a disk medium upon completion of data reception. When the writing of the data onto the disk medium is completed, the hard disk reports a status indicative of an execution result of the write command to the host and the write command is completed. In the write command from the host, information indicative of a write start address and the number of write blocks is shown. A hard disk drive recognizes the write command by an MCU through a host interface. The data from the host is temporarily stored into a data buffer and written onto the disk medium on a block unit basis. The status is reported by the two following methods:
I. a data reception command completing method of reporting the status at the time of completion of the data reception and completing the write command; and
II. a medium write command completing method of reporting the status at the time of completion of the writing of the data onto the disk and completing the write command.
According to the data reception command completing method, by finishing the write command upon completion of the data reception from the host, it is made easy to start the process of the next write command. That is, it is a command completing method whereby a command is issued to prewrite data in the data buffer. On the contrary, the medium write command completing method is a command completing method of writing data where the host confirms whether the data has normally been written onto the disk medium or not.
When a plurality of write commands are successively issued, the hard disk drive rearranges the plurality of commands in order from the write command of a short access time before execution of the plurality of write commands, thereby improving the command processing ability. Once the execution is started, the executing order is not changed after that. The start of the execution in this case denotes the start of data reception.
The data buffer is divided into some blocks called segments. The write command or read command of data is executed by using one segment. A purpose of dividing the data buffer into a plurality of blocks is that at the time of execution of the read command, data of the read command or subsequent data is held in the data buffer and, when the read command of the data held in the data buffer is issued as a subsequent command, the data is not read out from the disk medium but transferred directly from the data buffer to the host, thereby shortening a command process.
A purpose of prewriting data in the data reception command completing method is that all or a part of the write data has already been received into the data buffer before the completion of the movement of the head to the head sector of the issued write command, and the waiting of the disk medium due to the absence of the write data in the data buffer is reduced. That is, when data is not prewritten in the data buffer, the data has to be received during the movement of the head to the target sector. When the data is prewritten, the writing time of data onto the disk medium by the preceding write command is also included in the receiving time of the prewrite data from the host, so that there is sufficient time for data reception, and the waiting due to the absence of the write data in the data buffer does not easily occur. The execution of the data prewrite has, however, the following problems.
FIGS. 1A and 1B
show a flow of data when write commands of two blocks are issued from the host in the data reception command completing method of completing the write command at a point when the reception of the write data is completed.
FIG. 1A
shows a host interface and two write commands CMD
1
and CMD
2
which designate data of two blocks are successively issued. When the reception of the write commands CMD
1
and CMD
2
is completed at time t
1
, the hard disk drive receives data D
11
and D
12
of two blocks from the host by execution of the write command CMD
1
, stores them into the data buffer, reports a status STS
1
to the host upon completion of the data reception, and finishes the write command CMD
1
at time t
2
. The reception of data D
21
and D
22
of the next write command CMD
2
is consequently started and stored as prewrite data into the data buffer. A status STS
2
is reported upon completion of the data reception, thereby completing the write command CMD
2
at time t
4
.
FIG. 1B
shows a disk interface. In parallel to the reception of the data D
11
and D
12
of two blocks from the host, a head movement to a target sector designated by the write command CMD
1
is started and the writing of the data onto the disk medium is completed at time t
3
. As mentioned above, in the data reception command completing method of completing the command at a point when the reception of the write data is completed, since it is unnecessary to report a result of the data writing onto the disk medium to the host, a process of the next write command can be easily started in what is called a data prewrite. When the writing of data onto the disk medium fails in the data reception command completing method, however, since the initial write command has already been finished, a failure in the command is reported to the host without executing the write command next to the write command by which the data was finally prewritten. When a failure occurs in the disk writing of a plurality of commands successively issued from the host, only the command which finally fails is reported. There is consequently a problem such that the host has to perform the rewriting for all of the commands before the reported command. In order to solve the problem, the disk write command completing method in which the host can confirm that the data has normally been written onto the disk medium is usually adopted.
FIGS. 2A and 2B
show a flow of data when write commands of two blocks are issued from the host in the disk write command completing method of completing a command upon completion of writing of data onto the disk.
FIG. 2A
shows a host interface. The two write commands CMD
1
and CMD
2
designating data of two blocks are successively issued. When the reception of the write commands CMD
1
and CMD
2
is completed at time t
1
, the hard disk drive receives the data D
11
and D
12
of two blocks from the host by the execution of the write command CMD
1
and stores them into the data buffer.
FIG. 2B
shows a disk interface. When the reception of the data D
11
and D
12
of two blocks from the host is completed at time t
2
, the head movement to the target sector designated by the write command CMD
1
is started and the writing of the data D
11
and D
12
onto the disk medium is completed at time t
3
. Upon completion of the disk writing, the host interface reports the status STS
1
to the host, thereby completing the write command CMD
1
. Subsequently, the data D
21
and D
22
by the write command CMD
2
is received and, after the head movement, the data is written onto the disk. In recent years, however, the number of systems to each of which a plurality of hosts and a plurality of targets (hard disk drive and the like) are connected has been increasing. When prewriting of data is not performed, data reception is delayed because another target and the host are communicating, and a disadvantage such that data cannot be received until the head movement to the targe
Fujitsu Limited
Greer Burns & Crain Ltd.
Verbrugge Kevin
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