GB2423218A - Data storage system read/write channel optimiser which compares measured metrics of read channel with desired nominal and adjusts channel in response - Google Patents

Abstract

A read channel (3) for a data storage system (eg. magnetic/optical disk/disc/tape) has an associated optimisation controller (6) which monitors one or more of various metrics of the read channel. These metrics may be component parameters (eg amplifier gain) or signal characteristics (eg amplitude asymmetry). These measured metrics are then compared with a stored nominal value and if they differ by more than a threshold amount at least one optimisation action is taken. The action may include varying amplifier gain or adjusting a noise whitener or filter response. In general the optimisation action occurs in the read channel upstream of the metric measurement, however action downstream or in the write channel is also possible. The nature of the action to be taken may be prestored in a look-up table. The system may reverse actions which result in greater divergence of the measured metric from the nominal in subsequent monitoring.

Description

"OPTIMISATION OF A DATA READ SYSTEM AND A DATA READ/WRITE SYSTEM" THE

PRESENT INVENTION relates to a data read system and to a data read/write system having a mechanism for optimising the performance of the system. The present invention also relates to a method of optimising a data read system and a data read/write system. In particular, the present invention relates to a data read system and a data read/write system in the form of a data drive, which is capable of self-optimisation.

Owing to manufacturing variations in drives and media for data storage, as well the age and quality of the media, a particular drive may not be optimally configured for reading from and writing to a particular medium. As a result, data retrieval from the medium can prove problematic and/or the data capacity of the medium may be diminished. For example, problems are often encountered when attempting to read different tapes on different drives.

US Patent No. 6,252,731 describes an apparatus for optimising the performance of a disk drive comprising a disk-read head adjacent a disk, a servo circuit which controls the position of the disk-read head, and a read channel for decoding signals from the disk-read head to reconstruct data stored on the disk.

The rcad channel includes a channel quality monitor which generates a channel quality measurement indicative of the quality of the read channel.

Components of the read channel which have selcctively variable parameters are then optimised according to the channel quality measurements. For example, the tap weights of the transversal equaliser or the adaptive parameters of the adaptive prefilter are adjusted in response to the channel quality measurements.

Optimisation of the disk drive is achieved by first writing encoded test data to the disk. The variable parameter of the component of the read channel to be optimised (e.g. the tap weights of the transversal equaliser) is then set to a first value from a predetermined range of values. The encoded test data on the disk are then read and decoded by the read channel. The decoded data are then passed to the channel quality monitor, whereupon the data is compared against the test data originally written to the disk. The channel quality monitor generates a channel quality measurement based upon the sum of the bit errors between the written data and the read data. The variable parameter of the component to be optimised is then set to a second value from the predetermined range of values and the process repeated so as to generate a further channel quality measurement for this second value. This process is repeated for all values of the predetermined range of values such that a plurality of channel quality measurements is obtained, each measurement corresponding to a particular parameter value. The parameter of the component of the read channel is then set to that value for which the channel quality measurement is lowest. The entire process then is repeated for each of the components of the read channel to be optimised.

With the disk drive of US Patent No. 6,252,731, known data must first be written to the disk in order for the read channel of the drive to be optimised.

The disk drive cannot therefore be optimised for read-only media.

Additionally, optimisation is achieved by writing and then reading data using the same data channel. The disk drive is not, therefore, capable of being optimised for unknown data written to the disk by a different drive, i.e. data pattern or sequence for which the disk drive has no a priori knowledge.

Furthermore, once the disk drive is optimised, the variable parameters of the read channel components are locked. Accordingly, the drive is not capable of responding to any subsequent changes in the data signal which might occur during actual data retrieval. For example, there may be local variations in the quality of the medium, or the data may have been written to the medium using different drives and therefore have different coloured noise or signal outputs.

In a first aspect, the present invention provides a data read system comprising a read channel and an optimisation controller in communication with the read channel, the read channel comprising a plurality of components for processing a signal, and the optimisation controller configured to: communicate with the read channel during signal processing to measure a metric of one or more of the components; compare the measured metric against a stored nominal metric; and adjust one or more of the components in response to the comparison.

In a second aspect, the present invention provides a data read system comprising a read channel and an optimisation controller in communication with the read channel, the read channel comprising a plurality of components for processing a signal, and wherein the optimisation controller is configured.

In a third aspect, the present invention provides a read channel comprising a plurality of components for processing a signal and an optimisation controller configured to: measure a metric of one or more of the components during signal processing; compare the measured metric against a stored nominal metric; and adjust one or more of the components in response to the comparison.

In a fourth aspect, the present invention provides a data read/write system comprising a read channel, a write channel and an optimisation controller in communication with the read channel and the write channel, the read channel comprising a plurality of components for decoding data contained in a signal and the write channel comprising a plurality of components for encoding data in a signal, wherein the optimisation controller is configured to: measure a metric of one or more of the components of the read channel; compare the metric against a stored nominal metric; and adjust one or more of the components of the write channel in response to the comparison.

In a fifth aspect, the present invention provides a data drive comprising the data read system, the data read channel or the data read/write system.

In a sixth aspect, the present invention provides a method of optimising a read channel during signal processing, the read channel comprising a plurality of components for processing a signal, the method comprising the steps of: measuring a metric of one or more components; comparing the measured metric against a stored nominal metric; and adjusting one or more components in response to the comparison.

In a seventh aspect, the present invention provides a method of optimising a write channel of a data read/write system, the data read/write system comprising a data-read head for reading data stored on a data medium and outpufting in response a read-signal, a read channel comprising a plurality of components for processing the read-signal, a write channel comprising a plurality of components for encoding data into a write-signal, and a data-write head for receiving the write-signal and in response writing data to the data medium, the method comprising the steps of: writing data to a data medium; reading the data stored on the medium; measuring a metric of one or more components of the read channel during data read; comparing the measured metric against a stored nominal metric; and adjusting one or more components of the write channel in response to the comparison.

In an eighth aspect, the present invention provides means for optimising a read channel during signal processing, the read channel comprising a plurality of components for processing a signal, the means comprising: means for measuring a metric of one or more components; means for comparing the measured metric against a stored nominal metric; and means for adjusting one or more components in response to the comparison.

In a ninth aspect, the present invention provides means for optimising a write channel of a data read/write system, the data read/write system comprising a read channel having a plurality of components for decoding data contained in a signal and the write channel having a plurality of components for encoding data in a signal, and the means comprises: means for measuring a metric of one or more of the components of the read channel; means for comparing the metric against a stored nominal metric; and means for adjusting one or more of the components of the write channel in response to the comparison.

In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawing in which: Figure 1 is a schematic block diagram of a data read system in accordance with the present invention; and Figure 2 is a schematic block diagram of a data readlwrite system in accordance with the present invention.

The data read system 1 of the present invention and illustrated in Figure 1 comprises a data-read head 2 for reading encoded data stored on a medium and outputting in response an analogue readback signal, a read channel 3 for extracting modulated data from the analogue readback signal, an error correction circuit (ECC) 4 for correcting errors in the modulated data, a demodulator 5 for demodulating the data, and an optimisation controller 6 in communication with the read channel 3.

The read channel 3 comprises a preamplifier 7 which receives the readback signal from the data-read head 2; an automatic gain control circuit 8 comprising an analogue variable gain amplifier (analogue VGA) 9, an analogue filter 10, an analogue-to-digital converter (ADC) 11 and an automatic gain control (AGC) 12 arranged in feedback between the ADC 11 and the analgoue VGA 9; an amplitude asymmetry correction circuit 13; an oversampled FIR filter 14; an interpolated timing recovery circuit (ITR) 15 incorporating a second AGC; an adaptive FIR filter 16; a noise autocorrelator 17; and a maximum likelihood detector (MLD) 18 implementing a soft-output Viterbi algorithm (SOyA).

The components of the read channel 3 are common to conventional read channels and will not therefore be described here in any detail. Indeed, it should be understood that the data read system I of the present invention is not limited to the read channel 3 arrangement of Figure 1, but may instead include any conventional read channel arrangement.

It is perhaps worth noting that the AGC of the ITR 15, which controls the digital gain stage contained in the ITR 15, has a shorter time constant than that of the AGC 12 of the automatic gain control circuit 8. In particular, the time constants of the two AGCs are sufficiently different such that they do not battle each other for control.

In the embodiment of read channel 3 illustrated in Figure 1, the noise autocorrelator 17 measures the noise autocorrelation (i.e. the noise colour) of the channel signal at the output of the ITR 15 and adaptive FIR filter 16. The noise autocorrelation of the channel signal may, however, be measured at additional or alternative nodes of the read channel 3 prior to the MLD 18.

The optimisation controller 6 is in communication with the read channel 3 so as to measure a metric of one or more of the components of the read channel 3. A metric is a parameter or characteristic of a component of the read channel 3, which is programmable andlor adaptive, and reflects the current characteristics of the channel signal. The metric may be, for example, a variable parameter of a component (e.g. the gain of an amplifier) or a characteristic of the channel signal at the output of a component (e.g. the amplitude asymmetry of the signal).

The optimisation controller 6 then compares the measured metric against a nominal metric stored within the optimisation controller 6. The stored nominal metric corresponds to that value or characteristic which the optimisation controller 6 measures when the components of the read channel 3 to which the metric relates are perfectly optimised with respect to the readback signal. In other words, if those components of thc read channel 3 to which the measured metric relates are perfectly optimised with respect to the readback signal, the measured metric should correspond to the stored nominal metric.

The stored nominal metrics may be provided at manufacture as a standard set of metrics for a particular design of data read system.

Alternatively, the data read system 1 may undergo a lengthy initial calibration process during manufacture to obtain the stored nominal metrics for that particular data read system 1.

If a particular metric differs from the corresponding stored nominal metric by a predetermined threshold amount, the optimisation controller 6 adjusts in response one or more of the components of the read channel 3. For example, the optimisation controller 6 may adjust the set-up of the read channel equalisers, the amplifiers, or the MLD mode (e.g. trellis type). The components adjusted by the optimisation controller 6 need not necessarily be those components to which the measured metric relates. For example, the optimisation controller 6 may adjust the phase response of the analogue filter should the phase equalisation of the adaptive FIR filter 16, as measured by the optimisation controller 6, be higher than normal.

Generally speaking, the optimisation controller 6 adjusts components of the read channel 3 upstream from the point at which the metric is measured.

However, there may be instances for which optimisation is achieved through the adjustment of components downstream from the point at which the metric is measured. For example, the optimisation controller 6 may adjust the trellis type of the MLD 18 in response to noise autocorrelation measurements of the channel signal measured at points prior to the MLD 18, e.g. at the output of the ITR 15 or adaptive FIR filter 16.

The optimisation controller 6 stores a look-up table of which components to adjust in response to particular changes in one or more of the metrics. Accordingly, the optimisation controller 6 does not rely upon trialand-error adjustments of the components to optimise the read channel 1. As a result, the optimisation controller 6 is able to adjust and optimise components of the read channel 3 quickly and in realtime during data extraction from the readback signal.

The size and/or nature of the adjustment to a particular component by the optimisation controller 6 is preferably proportional to the magnitude of the difference between the measured metric and the stored nominal metric. For example, if the difference between the metric and the stored nominal metric is relatively large, the size of the adjustment to a particular component may similarly be large.

Once the one or more components have been adjusted by the optimisation controller 6, the metric is preferably remeasured. If the difference between the measured metric and the stored nominal metric has increased, the adjustment made by the optimisation controller 6 is reversed, i.e. the components are reset to their previous configuration or settings. The optimisation controller 6 may then apply an alternative (e.g. smaller) adjustment to the components. For example, if the optimisation controller 6 increased the gain of the preamplifier 7 by 40% and this results in the measured metric drifting to the other side of the nominal metric, but still far from the nominal metric, then the gain maybe increased instead by only 20%.

If the difference between the measured metric and the stored nominal metric decreases but nevertheless continues to be greater than the predetermined threshold amount, the optimisation controller 6 may further adjust the components until such time as either (a) the difference between the metric and the stored nominal metric is less than the predetermined threshold amount or (b) the difference between the metric and the stored nominal metric increases.

The SOVA of the MLD 18 measures the performance margin of the read channel 3 (i.e. the probability that the modulated data extracted by the read channel 3 is correct) and may itself be considered a metric. Various factors may reduce the performance margin of the read channel 3, such as noise in the system. As the performance margin of the read channel 3 decreases, the rate of bit errors in the decoding process increases. The performance margin of the SOVA may therefore be used to measure the benefit or penalty of adjusting the one or more components.

In a particularly preferred embodiment, the optimisation controller 6 measures the performance margin of the SOVA to determine whether an adjustment to one or more components has made a positive or negative contribution to the performance margin. If the adjustment to the components results in an increase in the performance margin, the adjustment to the components is retained. If, however, the performance margin decreases following the adjustment to the components, the adjustment is reversed and the components are reset to their previous configurations or settings.

Other methods of obtaining the performance margin of the read channel 3 may alternatively or additionally be employed. For example, the optimisation controller 6 may measure the signal-to-noise ratio of the channel signal at a point between the output of the ITR 15 and the input of the MLD 18, e.g. at the output of the ITR 15 or adaptive FIR filter 16. A high signal-to-noise ratio is indicative of a good performance margin.

Optimisation of the read channel 3 for two possible scenarios will now be described by way of example.

Different media (e.g. CDs, DVDs, tapes etc.) from different manufacturers often have different signal outputs. Consequently, the readback signal delivered by the data-read head 2 to the read channel 3 has an output that is lower, or possibly higher, than normal. This in turn causes the gain of the AGC 12 of the automatic gain control circuit 8 to run higher or lower than normal. In order that the read channel 3 may be optimised for different media, the optimisation controller 6 measures the gain of the AGC 12 of the automatic gain control circuit 8. If the gain of the AGC 12 is higher than the corresponding stored nominal metric, the optimisation controller 6 increases the gain in the preamplifier 7. Conversely, if the gain of the AGC 12 is lower than that of the stored nominal metric, the optimisation controller 6 decreases the gain in the preamplifier 7. The amount by which the gain of the preamplifier 7 is increased/decreased by the optimisation controller 6 may depend upon the magnitude of the difference between the measured gain of the AGC 12 and the stored nominal metric.

If the gain of the AGC 12 continues to run high/low after the gain of the preamplifier 7 has been adjusted, the optimisation controller 6 may continue to adjust the gain of the preamplifier 7 until such time as either the gain of the AGC 12 is within acceptable limits (i.e. the difference between the gain and the nominal metric is within the predetermined threshold amount) or no further improvement appears possible (i.e. the difference between the gain and the nominal metric cannot be further minimised). Preferably, the optimisation controller 6 measures the performance margin of the SOYA and accepts or rejects any adjustment to the gain of the preamplifier 7 if the performance margin respectively increases or decreases.

Different media, or media upon which data has been written using different drives, may include noise having a different colour to that expected.

As a result, the noise autocorrelation (i.e. the noise colour) of the channel signal is different to that expected. In order that the read channel 3 may be optimised for readback signals having different coloured noise, the optimisation controller 6 measures the noise autocorrelation of the channel signal at a point upstream from the MLD 18 and preferably immediately prior to the MLD 18. The noise autocorrelation of the channel signal is measured by the noise autocorrelator 17 at the output signal of either the ITR 15 or more preferably the adaptive FIR filter 16. If the measured noise autocorrelation of the signal is different to the stored nominal metric, the optimisation controller 6 causes the MLD 18 to employ a different trellis type (e.g. PR4, EPR4, noise whitened, etc.). Again, the optimisation controller 6 preferably measures the performance margin of the SOVA and accepts or rejects any change in the trellis type depending upon whether the performance margin increases or decreases.

It is to be understood that the two scenarios described above are provided by way of example only and that the read channel 3 and optimisation controller 6 may be configured differently according to the type of scenario that is likely to arise. Other possible scenarios that might arise are provided in the

table below.

The table lists the metric to be measured by the optimisation controller 6, the symptom of the metric, the potential cause of the symptom, and the adjustment to be made by the optimisation controller 6 to the components in order to remedy the symptom and thereby optimise the read channel 3. Again, it is to be understood that the scenarios listed in the table are provided by way of example only and are not exhaustive.

Metric Symptom Potential Cause Adjustment Gain of the AGC Running high/low Medium delivering Increase/decrease #1 lower/higher gain of readback signal preamplifier.

output than normal Noise Different to that Medium delivers Use different noise autocorrelation of expected noise having whitener mode in noise different colour to MLD autocorrelator that expected High frequency Increases with Spacing loss Increase high boost of adaptive time between the data- frequency boost of FIR filter read head and the analogue filter medium.

Signal dynamic Low/High Various Increase/decrease range at ADC gain target of output AGC #1 Amplitude Changes Readback signal Alter AAC circuit asymmetry at ITR amplitude to eliminate output asymmetry asymmetry changes Phase equalisation High Phase response of Adjust phase of settled adaptive medium changes response of FIR filter analogue filter Performance Decreases Poor adjustment Undo adjustment margin of SOVA following decision by adjustment optimisation controller The data read system 1 may include more than one read channel 3. For example, the data read system 1 may be an LTO tape drive having eight or sixteen read channels 3. Each read channel 3 of the data read system 1 may include a respective optimisation controller 6. Alternatively, the data read system 1 may include a single optimisation controller 6 that is common to and in communication with all read channels 3.

The optimisation controller 6 (or controllers) preferably measures and compares metrics from all read channels 3 of the data read system 1.

Adjustment of the components of the read channels 3 preferably occurs only when a particular metric drifts beyond its predetermined threshold for the majority of read channels 3. More preferably, adjustment only occurs when the metric drifts beyond its threshold for all read channels 3. Consequently, if a single read channel 3 (or the minority of read channels 3) is not optimised to the readback signal, no adjustment to the read channels 3 is made. Only when the majority of read channels 3 fail to optimise in the same manner, does adjustment of the components by the optimisation controller 6 take place.

The data read system 1 is preferably provided as a data drive, such as a tape or disk drive, with the output of the demodulator being fed to a host computer (not shown). Accordingly, the data read system 1 is capable of self- optimisation without any intervention by the host computer.

Preferably, the optimisation controller 6 is integral with and forms part of the read channel 3. Accordingly, the optimisation controller 6 is able to quickly measure the metrics of the read channel 3 and adjust the relevant components, if necessary. Additionally, the design of the read channel 3 and optimisation controller 6 is greatly simplified, thereby reducing manufacturing costs. In particular, there is no need to provide the read channel 3 with communication means for transmitting metric data to and receiving adjustment data from the optimisation controller 6.

The optimisation controller 6 may nevertheless be provided as a separate component within the data drive, e.g. a processor having instructions for receiving metric data from and transmitting in response adjustment data to the read channel 3.

The data read system 1 may alternatively include a host computer (not shown). In this particular embodiment, the optimisation controller 6 forms part of the host computer (e.g. provided in the form of a computer program). The read channel 3 and host computer are then provided with communication means, such as input/output ports, for transmitting metric data from the read channel 3 to the host computer (i.e. to the optimisation controller 6) and for transmitting adjustment data from the host computer (i.e. from the optimisation controller 6) to the read channel 3.

Whilst reference has thus far been made to the optimisation of a read channel 3 of a data read system 1, the present invention may be equally be applied to the optimisation of a write channel of a data read/write system.

Figure 2 illustrates a data read/write system 20 comprising a data-read head 2, a read channel 3, a data-write head 21, a write channel 22 and an optimisation controller 6 in communication with both the read channel 3 and the write channel 22.

The read channel 3 and write channel 21 may be provided as a single read/write channel. Additionally, the data-read head 2 and data-write head 21 may be provided as a single read/write head.

In use, the data read/write system 20 first writes encoded data to a medium using the data-write head 21 and write channel 22. There are no special constraints or limitations on the data being written to the medium. In particular, it is not necessary that for the data to consist of a constant frequency data pattern. Instead, the data wriften to the medium may be normal user data.

The encoded data are then read from the medium using the data-read head 2 and read channel 3. The programmable and adaptive components of the read channel 3 are set to nominal values, i.e. values which would be employed in read channels of generic data read systems (i.e. generic tape or disk drives).

The optimisation controller 6 then measures metrics of the read channel 3 and compares the metrics against stored nominal metrics. This time, however, if a metric differs from the corresponding stored nominal metric beyond its predetermined threshold, the optimisation controller 6 adjusts one or more components of the write channel 22.

Preferably, once components of the write channel 22 have been adjusted, encoded data is again written to and subsequently read from the medium. The optimisation controller 6 then remeasures the metrics of the read channel 3. If the difference between the metric and the stored nominal metric has increased, the optimisation controller 6 reverses the adjustment made to the components of the write channel 22. Alternatively, or additionally, the adjustment made to the components of the write channel 22 may be reversed if the performance margin of the read channel 3 is reduced as a result of the adjustment.

With the data read system 1 of the present invention, seif-optimisation of the system 1 occurs in realtime during data extraction. Importantly, the system I does not rely upon reading known data in order to seif- optimise. Moreover, by seif-optimising during data extraction, the system 1 is able to respond to sudden changes in the readback signal, such as might occur due to changes in the quality of the medium, or where the encoded data has been written to the medium using different drives.

With the data read/write system 20 of the present invention, the write channel 22 is optimised such that encoded data is written to a particular type of medium in a manner that is best optimised for generic data read systems incapable of seif-optimisation, i.e. generic tape of disk drives.

In employing an optimisation controller 6 that adjusts specific componentsof the read channel 3 or write channel 22 in response to measured metrics, optimisation of the data read system I or data read/write system 20 may be achieved much quicker than by trial-and-error methods of optimisation.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (1)

1. A data read system comprising a read channel and an optimisation controller in communication with the read channel, the read channel comprising a plurality of components for processing a signal, and the optimisation controller configured to: communicate with the read channel during signal processing to measure a metric of one or more of the components; compare the measured metric against a stored nominal metric; and adjust one or more of the components in response to the comparison.

2. A system according to Claim 1, wherein the stored nominal metric corresponds to a metric measurement made when the components to which the metric relates are optimised.

3. A system according to Claim 1 or 2, wherein the optimisation controller is configured to adjust the components should the difference between the metric and the stored nominal metric exceed a threshold.

4. A system according to Claim 3, wherein the optimisation controller is further configured to remeasure the metric after the components have been adjusted, and reverse the adjustment of the components should the difference between the remeasured metric and the stored nominal metric be greater than the difference between the previously measured metric and the stored nominal metric.

5. A system according to any one of the preceding claims, wherein the optimisation controller is further configured to: measure a further metric of one or more components prior to adjusting the components, the further metric representing a measure of the performance margin of the read channel; remeasure the further metric after adjusting the components; and reverse the adjustment of the components should the further metric before adjustment be better than that after adjustment.

6. A system according to Claim 5, wherein one of the components of the read channel is a maximum likelihood detector implementing a soft-output Viterbi algorithm, and the further metric is the output of the softoutput Viterbi algorithm.

7. A system according to any preceding claim, wherein the optimisation controller adjusts components that are upstream from the position at which the metric is measured.

8. A system according to any preceding claim, wherein the optimisation controller measures a plurality of metrics of the components of the read channel, and the optimisation controller stores for each metric a nominal metric and a threshold.

9. A system according to Claim 8, wherein the optimisation controller includes a look-up table of which components to adjust in response to a particular metric differing from the respective stored nominal metric by more than the respective threshold.

10. A system according to any preceding claim, wherein the system further comprises an error correction circuit and the optimisation controller measures a metric upstream from the error correction circuit.

11. A system according to any preceding claim, wherein the optimisation controller is configured to measure the metric and compare the measured metric against a stored nominal metric during processing by the read channel of a signal containing unknown data.

13. A data read system comprising a read channel and an optimisation controller in communication with the read channel, the read channel comprising a plurality of components for processing a signal, and wherein the optimisation controller is configured to: communicate with the read channel during signal processing to measure a metric of one or more of the components, the metric comprising a set of possible attributes; and adjust one or more of the components in response to the attribute of the measured metric.

14. A system according Claim 13, wherein the optimisation controller is configured to measure the metric during processing by the read channel of a signal containing unknown data.

15. A read channel comprising a plurality of components for processing a signal and an optimisation controller configured to: measure a metric of one or more of the components during signal processing; compare the metric against a stored nominal metric; and adjust one or more of the components in response to the comparison.

16. A data read/write system comprising a read channel, a write channel and an optimisation controller in communication with the read channel and the write channel, the read channel comprising a plurality of components for decoding data contained in a signal and the write channel comprising a plurality of components for encoding data in a signal, wherein the optimisation controller is configured to: measure a metric of one or more of the components of the read channel; compare the metric against a stored nominal metric; and adjust one or more of the components of the write channel in response to the comparison.

17. A data drive comprising the system or read channel of any one of Claims ito 12 and l4to 19.

18. A data drive according to Claim 17, wherein the data drive is an LTO tape drive.

19. A method of optimising a read channel during signal processing, the read channel comprising a plurality of components for processing a signal, the method comprising the steps of: measuring a metric of one or more components; comparing the measured metric against a stored nominal metric; and adjusting one or more components in response to the comparison.

20. A method according to Claim 19, wherein the method further comprises the steps of: remeasuring the metric after the step of adjusting the components; comparing the rcmeasured metric against the stored nominal metric; and reversing the adjustment of the components should the difference between the remeasured metric and the stored nominal metric be greater than the difference between the previously measured metric and the stored nominal metric.

21. A method according to either Claim 19 or 20, wherein the method further comprises the step of: measuring a further metric of one or more components prior to the step of adjusting the components, the further metric representing a measure of the performance margin of the read channel; remeasuring the further metric after the step of adjusting the components; and reversing the adjustment of the components should the further metric before adjustment be better than that after adjustment.

22. A method of optimising a write channel of a data read/write system, the data read/write system comprising a data-read head for reading data stored on a data medium and outputting in response a read-signal, a read channel comprising a plurality of components for processing the readsignal, a write channel comprising a plurality of components for encoding data into a write- signal, and a data-write head for receiving the write-signal and in response writing data to the data medium, the method comprising the steps of: writing data to a data medium; reading the data stored on the medium; measuring a metric of one or more components of the read channel during data read; comparing the measured metric against a stored nominal metric; and adjusting one or more components of the write channel in response to the comparison.

23. Means for optimising a read channel during signal processing, the read channel comprising a plurality of components for processing a signal, the means comprising: means for measuring a metric of one or more components; means for comparing the measured metric against a stored nominal metric; and means for adjusting one or more components in response to the comparison.

24. Means for optimising a write channel of a data read/write system, the data read/write system comprising a read channel having a plurality of components for decoding data contained in a signal and the write channel having a plurality of components for encoding data in a signal, and the means comprises: means for measuring a metric of one or more of the components of the read channel; means for comparing the metric against a stored nominal metric; and means for adjusting one or more of the components of the write channel in response to the comparison.

25. A data read system substantially as hereinbefore described with reference to and as shown in Figure 1.

26. A data read/write system substantially as hereinbefore described with reference to and as shown in Figure 2.

27. A read channel substantially as hereinbefore described with reference to and as shown in the accompanying drawings.