Patent ID: 6026468
Filing Date: 2000-02-15
Classification: G06F,G11B

Abstract:
A method of controlling a magnetic tape unit, in which the magnetic tape unit is controlled in response to a command from a host processor, while temporarily storing into a data buffer a data block to be written onto a magnetic tape by the magnetic tape unit and a data block read from the magnetic tape by the magnetic tape unit, and storing into a command queue commands concerning the data blocks in the data buffer in the order in which the commands are executed, and the method comprising the steps of:when a read back command to compressed data recorded on the magnetic tape is received from the host processor, causing the magnetic tape unit to read a plurality of data blocks in a backward direction from the magnetic tape;when a read position of the magnetic tape unit reaches a position at which a predetermined condition is met, causing the magnetic tape unit to read in a forward direction from the magnetic tape the plurality of data blocks in the range between the position and a start position of the read back command so as to write the plurality of data blocks read in the forward direction into the data buffer;storing read commands concerning the data blocks read in the forward direction into the command queue in reverse order to how the data blocks are read by the magnetic tape unit; andthereafter sequentially reading, in response to a read command from the host processor, the data blocks in the data buffer according to the read commands in the command queue so as to transfer the data blocks to the host processor after data expansion.