Patent Application
20060082912
The present invention relates to cleaning one or more read/write heads of a magnetic tape recording system using a cleaning tape.
A common form of storage medium for use in storing computer data takes the form of a magnetically recordable tape that is moved relative to magnetic read/write heads. One form of magnetic tape data recording system comprises a helical-scan tape deck in which the tape from a tape cartridge passes at a predetermined angle across a rotary head drum. In operation the tape is drawn from a supply reel to a take-up reel by rotation of a capstan against which the tape is pressed by a pinch roller. The head drum houses two write heads angularly spaced by 180° and two read heads also angularly spaced by 180°.
The magnetic tape is subject to wear and deterioration and the recording system is subject to head clogs. The result is that errors occur in the read/write process. Whilst some errors can be corrected by a format of data encoding that includes error correction within the format definition, nevertheless it is necessary to take steps to clean the read/write heads so that errors that are attributable to dirty heads are eliminated or reduced.
It is already known to clean the magnetic read/write heads by inserting a cleaning tape cartridge into such a magnetic data recording system. The cleaning tape cartridge contains a cleaning tape that has no recorded data but is pulled through the data recording system to clean the heads. The cleaning tape is advanced by a chosen increment to clean the heads. The increment of cleaning tape that is pulled through the data recording system is contaminated by the cleaning process and cannot be re-used. A fresh increment of the cleaning tape must be advanced when a cleaning operation is performed the next time.
A disadvantage of the conventional method of cleaning the heads of the data recording system by a cleaning tape is that there is no indication of how effective the cleaning operation has been until a data recording tape has been inserted into the system and data recording has been undertaken. This may result in the situation where an unsatisfactory cleaning operation has resulted and the cleaning operation has to be repeated all over again. Alternatively, the length of cleaning tape that is incremented to clean the heads is deliberately chosen to be longer than necessary for a successful cleaning operation in an attempt to ensure the success of the cleaning operation. This may result in wastage of the cleaning tape.
It has already been proposed in U.S. Pat. No. 5,381,292 to clean a section of a magnetic tape where read/write errors occur. In a first step, the tape is spooled to one end of the tape at 300 times the normal read or write speed. In a second step, the tape is spooled to the other end of the tape at 300 times the normal read or write speed. In the third step, the tape is moved to place the heads over the section where the errors occurred.
It has also been proposed in published U.S. patent application 20030169529 to use a cleaning cartridge in a magnetic recording system, the cleaning tape having a pattern signal recorded on a predetermined segment that is read by a magnetic head in the system. On-site adjustments can be made to parameters of the magnetic head by reading the pattern from the cleaning tape when the user directs a cleaning operation. A failure of the magnetic head can also be detected and predicted through the cleaning operation.
According to the present invention, there is now provided a method of cleaning one or more read/write heads of a magnetic tape recording system, the method comprising;
setting a magnetically recordable cleaning tape in the system,
instructing the system to perform a sequence of operations including pulling a portion of the cleaning tape through the system so as to clean the or each head, and
recording on the cleaning tape a log of the said sequence of operations providing a history of usage of the cleaning tape.
Further, according to the present invention, there is provided a magnetic recording system having one or more read/write heads and adapted to receive a magnetically recordable cleaning tape;
the system being programmed;
to perform a sequence of operations that includes pulling a portion of the cleaning tape through the system so as to clean the or each head, and
to record on the cleaning tape a log of the said sequence of operations providing a history of usage of the cleaning tape.
The invention will now be described, by way of example only, by reference to the accompanying drawings in which;
Referring to
The host system 11 has at least one central processing unit (CPU) and a memory to store the controlling software application. The interface 13 connecting the host system 11 to the controller 12 may be any suitable proprietary standard bus known to those skilled in the art.
The drive mechanism 16 includes electrical and mechanical components that receive, position and access tape cartridges. The drive mechanism has components to lock a tape cartridge in place, an ejection motor and read/write heads. The drive engine 15 is a data processor that is programmed to supervise the operations of the drive mechanism 16 and to manage the flow of data to be recorded in or read from a tape cartridge 17 received in the drive 14. A cleaning cartridge that stores a cleaning tape may be loaded in the drive 14 to effect cleaning of the read/write heads. The drive engine 15 has a program to control the process of cleaning the read/write heads by means of the cleaning tape as will be explained in greater detail below. The drive engine 15 is programmed to calculate and register the error rate of data that is recorded on a tape cartridge that is loaded in the drive 14.
Referring to
Referring again to
On the next load of the cleaning cartridge, the determination in the step 44 will indicate that this is not the first load of the cartridge. In this case, the process continues to the step 49 where the tape drive rewinds the tape 51 from its prior finishing position so that the read heads 28C and 28D are positioned to read the log recorded in the first of the areas 56. The placement of the tape 51 in position to enable the log to be read is shown diagrammatically by the arrow 57 in
If the cleaning tape cartridge is loaded for a third time, the determination in the step 44 will again indicate that this is not the first load of the cartridge. As before, the process continues to the step 49 where the tape drive rewinds the tape 51 from its prior finishing position so that the read heads 28C and 28D are positioned to read the updated log at the end of the tape portion 53. The placement of the tape 51 in position to enable the log to be read is shown diagrammatically by the arrow 58 in
The process continues to the cleaning step 46 as before. The process of cleaning will, in this case, use the tape portion 54 of the cleaning tape 51. If, however, the cleaning operation is unsatisfactory using any of the tape portions, an extended cleaning operation is conducted using an extended portion of the tape 51. Thus, assuming the cleaning operation using the tape portion 54 is unsatisfactory, an extended cleaning operation is effected using the extended cleaning portion 55. Following the extended cleaning operation, the write heads 28A and 28B are used in step 47 to record an update of the sequence of data in the log using the tape area 56 at the end of the extended tape portion 55.
The method of determining whether a cleaning operation is unsatisfactory or not, and therefore whether an extended cleaning operation is required, will be described with reference to
Referring to
Referring now to
In step 72 the cleaning tape is advanced at the normal recording speed, clearing the previously recorded area on the tape, so that the tape portion 52 of cleaning tape is presented to the heads 28A, 28B, 28C and 28D. The heads 28A and 28B again record a sequence of test data on the cleaning tape. In step 73, the start time of an error rate test is monitored. A check is performed in step 74 to determine whether the cleaning tape has been incremented for a time up to the end of the fixed test interval of X seconds. The error rate of the recorded test data is determined in step 75 and stored in step 76 by means of the drive engine 15.
In step 77, the error rate stored in step 76 is compared with the initial error rate to determine the extent to which the error rate has improved as a result of the cleaning operation. A value representing that improvement by reference to the initial error rate is generated in the step 77. A check is made in step 78 to determine if the value generated in the step 77 represents a drop in the error rate down to a target value that is referenced to the initial error rate. If so, the cleaning cartridge is ejected from the drive 14 in step 79. An indication of a successful cleaning operation is provided in step 80 to an operator of the system 10.
If the check performed in the step 78 shows that the drop in the error rate has not reached the target value, the process continues to a step 81 where the counter initially set to zero in step 41 of
If the check performed in the step 82 shows that the counter has been incremented to its maximum value, the process moves on to the step 83. In the step 83, an error flag is set to indicate a failed cleaning operation. This flag can be read by the host 11, if desired, whereby the host will be informed that the clean attempt has failed.
In an alternative embodiment of the invention, the check carried out in step 78 may be a check to determine if the error rate calculated in step 77 is below a fixed predetermined target value for the error rate. In this case the target value is not referenced to an initial value of error rate but is an absolute value. In this case also, the steps 60 to 63 may be dispensed with since an initial value of error rate is not required.
The current data in the tape log is registered within the tape drive preparatory to each cleaning operation. As described above, after a cleaning operation, the log data is updated and rewritten to the next tape area 56. The data itself includes the cartridge identifier pattern (CIP) representing the manufacturer of the cleaning tape cartridge, a serial number of the tape 51, and diagnostic information. The diagnostic information includes cumulative information on the history of usage of the cleaning tape 51 and comprises a history of the number of times the tape 51 has been used for cleaning, data on the number of times the calculated error rate is above the target error rate (i.e. the number of times an extended cleaning operation has been necessary), an identification by means of a serial number of each of the tape drives that have been cleaned and a flag indicating if the cleaning cartridge is faulty or has expired within a date recorded on the cartridge. The log is useful in tracking the performance of different cleaning cartridges so as to build up usage models of behaviour that can be used to support recommendations to end users of cleaning tape cartridges. The recommendations can be made with reference to the serial numbers of the cleaning tape cartridges and the tape drives that are cleaned by the tape cartridges.
What has been described is a method of cleaning the read/write heads of a magnetic tape data recording system by means of a magnetically recordable cleaning tape in which the system is instructed to perform a sequence of operations including pulling a portion of the cleaning tape through the system so as to clean the heads, and to record on the cleaning tape a log of the sequence of operations. The log provides a history of usage of the cleaning tape.
In providing the history of usage, the log may be recorded to indicate the number of times the calculated error rate is above the target error rate, to identify the magnetic tape recording system and to record whether a pre-recorded date associated with the tape has expired. The log may be recorded to provide a history of the number of cleaning operations in which the cleaning tape has been used and to provide a history of the number of times an increased length of the cleaning tape is employed.
While the invention has been described in relation to a magnetic tape drive which is in the form of a helical-scan tape deck in which tape from a tape cartridge passes at an angle across a rotary head drum, the invention may also be applied to other forms of magnetic tape recording system including, for example, a magnetic tape cartridge system such as the Linear-Tape-Open (LTO) system.
Furthermore, while the drive engine 15 has been described as having a program to control the process of cleaning the read/write heads by means of the cleaning tape and recording a log of data on a tape cartridge that is loaded in the drive, the drive engine 15 may alternatively be programmed by the incorporation of a suitably constructed application specific integrated circuit (ASIC) into the drive engine 15.
