1. Field of the Invention
The present invention relates to hard-disk drive systems, and, in particular, to detecting defects on the surface of hard-disk drive platters.
2. Description of the Related Art
FIG. 1 shows a simplified block diagram of a prior-art hard-disk drive (HDD) system 100. HDD system 100 has hard-drive (HD) controller 104, which manages a number of functions of HDD system 100. One function is handling the transfer of data to and from HDD system 100 during read and write operations. During write operations, incoming digital data is received from external hardware through a user interface 102, such as a SATA (serial advanced technology attachment) or IDE (integrated or intelligent drive electronics) interface. The incoming data is stored in queues in HD controller 104 and scheduled for write operations. After a write operation is scheduled, the incoming data is provided to recording channel 108 via non-return-to-zero (NRZ) bus 106, and HD controller 104 directs recording channel 108 to begin the writing operation.
The incoming data is encoded by recording channel 108 and converted from digital to analog format to generate an analog signal. Encoding may be performed using, for example, run-length limited (RLL) encoding techniques, error-correction encoding techniques such as low-density parity-check (LDPC) encoding or Reed Solomon encoding, a combination of the above, or other suitable techniques for encoding data that is to be written to an HD platter. Recording channel 108 then directs preamplifier 112 to enter into a writing mode using one or more control signals 110 that are transmitted directly between recording channel 108 and preamplifier 112. Alternatively, HD controller 104 could direct preamplifier AD to enter into the writing mode. Preamplifier 112 amplifies the analog signal such that the resulting amplified signal has sufficient power to drive write head 118. Write head 118 is typically constructed with an inductive element that produces a magnetic field when powered. The magnetic field, which varies with the amplified signal level (e.g., high or low), writes data to platter 124 by altering a magnetic recording material that is coated on the face of platter 124. Typically, platter 124 is partitioned into concentric rings called tracks, and each track is further partitioned into smaller sections called sectors. The incoming data is written to the sectors, each of which holds a specified amount of data (e.g., 512 bytes). Although only one platter is shown in FIG. 1, conventional HDD systems may have more than one platter and each additional platter may be served by additional write and read heads.
During read operations, HD controller 104 (i) receives a request for data from external hardware through user interface 102 and (ii) directs recording channel 108 to begin read operations. Recording channel 108 in turn directs preamplifier 112 to enter into a reading mode using the one or more control signals 110 that are transmitted directly to preamplifier 112. Preamplifier 112 provides a bias current to read head 120, which reads data from the sectors on platter 124. Read head 120 is typically constructed with a magneto resistive (MR) element having resistive properties that change as the magnetic field of platter 124 changes. As the resistive properties of the MR element change, a corresponding change in voltage is recorded as a reproduced, or playback, analog data signal. The outgoing analog data signal is then amplified by preamplifier 112 and provided to recording channel 108.
Recording channel 108 (i) converts the outgoing analog data signal from analog to digital format, (ii) filters the outgoing digital signal, and (iii) decodes the outgoing digital signal. Decoding may be performed using, for example, RLL decoding, partial-response maximum-likelihood (PRML) decoding, Viterbi decoding, and error-correction decoding techniques such as Reed Solomon decoding or LDPC decoding, or a combination of the above methods. The decoded data is then provided to HD controller 104 via NRZ bus 106 for transfer to external hardware through user interface 102.
Another function of HD controller 104 is the radial positioning of write head 118 and read head 120 relative to platter 124. Servo data on platter 124 (i.e., positioning data that is prerecorded on and subsequently read from platter 124) is used to determine the location of write head 118 and read head 120 over platter 124. This data is interpreted by HD controller 104, which generates and provides positioning commands to motor controller 126. Motor controller 126 drives spindle motor 128, which maintains a desired (e.g., constant) rotation speed of platter 124 about its axis. Motor controller 126 also drives voice coil motor (VCM) 114, which positions write head 118 and read head 120 radially over platter 124. Write head 118 and read head 120 are typically separate components that are fabricated together on a head assembly 122, which is attached to VCM 114 via a single positioning arm 116.
During the manufacturing process, a number of defects may arise in the magnetic recording material on platter 124. When a user writes data to or reads data from defective areas on platter 124, errors may arise in storing or recovering the data. To minimize the likelihood of these errors, HDD system manufacturers typically flag defects during the manufacturing process. Flagged defects that negatively affect reading and writing operations are removed from the final usable storage space of the HDD system by placing the defect locations in a table. During subsequent read and write operations, the HDD system references this table to avoid using the defective locations.
Determining which defects merit mapping out of the final usable space is a balancing act. On one hand, mapping too few areas of the platter out of the final usable storage space could result in reliability issues. If sufficient areas are not mapped out, then the manufacturer will incur costs and other problems due to failing HDD systems. On the other hand, mapping too many areas of the platter out of the final usable storage space could result in yield problems. In such a case, the intended capacity of the HDD system might not be achievable.
Traditionally, HDD system manufacturers have employed a prior-art two-pass method to detect defects on the face of a platter. The first pass is performed using a non-final disk formatting and the second pass is performed using a subsequent (and possibly final) disk formatting. In general, the first defect-detection pass is performed by writing a fixed data pattern to a track on the disk. The track is then read back and the recovered (i.e., outgoing) signal is analyzed for defects using traditional flaw-scan techniques (as described below). Relatively major defects are flagged and mapped out of the final usable space of the HDD system. Defects that are marginal (i.e., not relatively major and not relatively minor) are flagged and mapped to the subsequent drive formatting so that they may be tracked during the second pass or processed differently with other techniques. This process is repeated for all tracks on the platter, and the first pass is completed once all tracks have been analyzed.
The second defect-detection pass is performed by writing a real user data pattern to a track on the platter. Prior to writing the user data pattern, the data is encoded by the recording channel using, for example, run-length limited (RLL) encoding techniques, error-correction encoding techniques such as low-density parity-check (LDPC) encoding or Reed Solomon encoding, a combination of the above methods, and/or other suitable techniques for encoding data that is to be written to an HD platter. The track is then read back and a data-integrity check is performed by decoding the encoded user data pattern to recover the original user data pattern. Portions of the user data pattern that may be properly decoded are maintained in the final usable space, while portions of the user data pattern that cannot be properly decoded are flagged as defective. To further understand the prior-art two-pass defect-detection method, consider FIGS. 2-7.
FIG. 2 shows a simplified representation of one section 200 of a track on a HDD platter having a non-final disk formatting. This non-final disk formatting is typically used for the first pass of the prior-art two-pass defect-detection method. As shown, section 200 is partitioned into several areas. These areas, which are not actually marked on the face of the disk, are each mapped to one of three types of fields: a fixed-pattern field, an inter-sector gap, or a servo field. Each fixed-pattern field is reserved for writing a fixed data pattern during the first defect-detection pass. Each servo field is reserved for storing servo (i.e., positioning) data. Typically, the servo data is written at the time of the non-final formatting or sometime prior to the start of the first defect-detection pass. Each inter-sector gap serves as a buffer between two other types of fields, such as between a servo field and a fixed-pattern field. These gaps are not intended for writing data; however, at times, data may be inadvertently written over the inter-sector gaps due to, for example, the effects of jitter.
As shown in FIG. 2, section 200 is formatted to have two fixed-pattern fields 206-1 and 206-2, four inter-sector gaps 204-1, 204-2, 204-3, and 204-4, and three servo fields 202-1, 202-2, and 202-3. First fixed-pattern field 206-1 is flanked by first and second inter-sector gaps 204-1 and 204-2, and second fixed-pattern field 206-2 is flanked by third and fourth inter-sector gaps 204-3 and 204-4. First inter-sector gap 204-1 serves as a buffer between first servo field 202-1 and first fixed-pattern field 206-1, second inter-sector gap 204-2 serves as a buffer between first fixed-pattern field 206-1 and second servo field 202-2, third inter-sector gap 204-3 serves as a buffer between second servo field 202-2 and second fixed-pattern field 206-2, and fourth inter-sector gap 204-4 serves as a buffer between second fixed-pattern field 206-2 and third servo field 202-3. This formatting is repeated for the remainder of the track on which section 200 resides and is similar throughout the remainder of platter 124 (i.e., the remaining tracks). Tracks that are located closer to the center of platter 124 than section 200 may have smaller fixed-pattern fields due to their smaller circumferences, while tracks located farther from the center of platter 124 than section 200 may have larger fixed-pattern fields due to their larger circumferences.
FIG. 3 graphically illustrates a prior-art sequence 300 for writing a fixed data pattern to first fixed-pattern field 206-1 of section 200 shown in FIG. 2. At time t1, HD controller 104 enables the servo mode and performs a servo operation from times t1 to t2 to locate first servo field 202-1. After the servo mode is disabled at time t2, HD controller 104 of FIG. 1 directs recording channel 108 to enable the write mode at time t3. The relatively brief delay from times t2 to t3 corresponds to write head 118 passing over inter-sector gap 204-1 without writing the fixed data pattern. As shown in close-up 302, once the write mode is enabled at time t3, writing of the fixed data pattern to platter 124 may be further delayed until time t3a due to a delay in powering up pre-amplifier 112. The powering up of preamplifier 112 may be timed such that write head 118 begins writing the fixed data pattern as soon as inter-sector gap 204-1 has passed.
The write mode is asserted until time t4, and during this time, the fixed data pattern is written to first fixed-pattern field 206-1. The fixed data pattern, which may be generated by recording channel 108, does not pass through the normal encoding path of recording channel 108 before it is written (e.g., the fixed data pattern doesn't undergo encoding such as error-correction encoding and RLL encoding). The fixed data pattern may be a non-return-to-zero (NRZ) data pattern, such as an iT data pattern that alternates every i bits, where i is an integer. For example, a 2T pattern (i.e., i=2), having a pattern that alternates every two bits (i.e., 11001100 . . . ), is often used.
As shown in close-up 304 of FIG. 3, once the writing mode is disabled at time t4, writing of the fixed data pattern to platter 124 may continue for a relatively brief period of time until writing of the fixed data pattern is completed (i.e., at time t4a). Termination of the write mode may be planned such that the writing of the fixed data pattern is completed in time to leave inter-sector gap 204-2 between first fixed-pattern field 206-1 and second servo field 202-2. At time t5, the servo mode is again enabled and a servo operation is performed to locate the next fixed-pattern field for writing (e.g., second fixed-pattern field 206-2). The writing process described above is repeated for the next fixed-pattern field, and then is subsequently repeated for the remainder of the track in which section 200 resides. After the entire track has been written, the track is read back in a clockwise direction and analyzed by recording channel 108.
FIG. 4 graphically illustrates a prior-art sequence 400 for reading a fixed data pattern from first fixed-pattern field 206-1 of section 200 shown in FIG. 2. At time t1, HD controller 104 enables the servo mode and performs a servo operation from times t1 to t2 to locate first servo field 202-1 corresponding to fixed-pattern field 206-1. After the servo mode is disabled, the read mode is enabled at time t3. The relatively brief delay from times t2 to t3 corresponds to read head 120 passing over inter-sector gap 204-1 without reading the gap. Since inter-sector gap 204-1 is not read, it is also not analyzed for defects. Once the read mode is enabled, there is a lock period 208-1, as shown in close-up 402, in which recording channel 108 performs a zero-phase start, timing acquisition, and gain acquisition to lock on the fixed data pattern written to fixed-pattern field 206-1. During lock period 208-1, the defect-detection capabilities of recording channel 108 are limited, and thus, defect detection is not as effective during lock period 208-1 as it is after recording channel 108 has locked on the fixed data pattern.
Optimally, recording channel 108 would begin acquiring the lock at the beginning of the fixed data pattern. However, as shown in close-up 402 of FIG. 4, the read mode might not be enabled until after the beginning of the fixed data pattern has actually passed (i.e., read mode might be enabled at time t3 as opposed to time t2a). This relatively short delay between the beginning of the fixed data pattern and the assertion of the read mode may be introduced to ensure that recording channel 108 does not inadvertently attempt to perform the lock over inter-sector gap 204-1. In the event of such a delay, the portion of the fixed data pattern passed over from times t2a to t3 will not be read, and consequently, will not be analyzed for defects.
Once recording channel 108 has obtained a lock on the fixed data pattern in first fixed-pattern field 206-1, the fixed data pattern is read back and analyzed. When a 2T pattern has been written to platter 124, the recovered (i.e., outgoing) signal generally forms a sine wave. In analyzing the recovered signal, recording channel 108 does not process the signal through the normal decoding path of recording channel 108. In other words, recording channel 108 does not process the recovered signal using decoding such as error-correction decoding, PRML decoding, RLL decoding, or other typical decoding because the fixed data pattern was not encoded during the write operation. Note, however, that the recovered signal may still be processed using a Viterbi detector.
Recording channel 108 may analyze the recovered signal using any of a number of traditional flaw-scan techniques that exploit the recording channel's knowledge of the repetitive pattern. These flaw-scan techniques, which are typically performed after the recovered signal has been converted from analog-to-digital format, may include, for example, looking for distortions in the recovered signal (i) by cross-correlating the recovered signal with the expected signal, (ii) by verifying that the peaks of the recovered signal are in the proper position, and (iii) by comparing the peaks of the recovered signal to a threshold. If the peaks are not in the proper position or are below the threshold, then the area is flagged as defective. Further, the log-likelihood ratios that are generated by a Soft Output Viterbi detector or other soft detector may be used as potential flags for defective areas. Relatively long regions of defects in the recovered signal are flagged and may be mapped out of the usable disk space altogether. Areas of defects that are marginal (i.e., not relatively major and not relatively minor) are flagged and mapped to the subsequent (and possibly final) drive formatting so that they may be appropriately processed during the second defect-detection pass described below or may be more thoroughly examined by other defect detection methods. As an example, FIG. 2 shows the location of three exemplary marginal defects 210-1, 210-2, and 210-3 flagged on section 200 relative to the non-final formatting. First and second defects 210-1 and 210-2 are located in first fixed-pattern field 206-1 and third defect 210-3 is located in second fixed-pattern field 206-2.
Referring again to FIG. 4, the reading mode is disabled at time t4, which, as shown in close-up 404, corresponds to the end of the fixed data pattern and to the beginning of inter-sector gap 204-2. Note that inter-sector gap 204-2 does not contain the fixed data pattern, and consequently, this gap is neither read nor analyzed for defects. At time t5, the servo mode is enabled, and a servo operation is performed to locate the next fixed-pattern field to analyze for defects (e.g., second fixed-pattern field 206-2). The reading operation described above is repeated for the next fixed-pattern field, and then is subsequently repeated for the remainder of the track in which section 200 resides. After the full track has been analyzed, the writing and reading operations of the first defect-detection pass are repeated on a track-by-track basis for the remaining tracks on platter 124. The first defect-detection pass is completed once all tracks on platter 124 have been analyzed for defects. After the first pass is completed, platter 124 is formatted using a subsequent formatting, and the second defect-detection pass is performed using the subsequent formatting.
FIG. 5 shows a simplified representation of a subsequent disk formatting on the same section 200 of a track shown in FIG. 2. This subsequent formatting is typically the final formatting that is used by a consumer to write and read data. As shown, servo fields 202-1, 202-2, and 202-3 and the inter-sector gaps 204-1, 204-2, 204-3, and 204-4 remain unchanged from the non-final formatting of FIG. 2. Fixed-pattern fields 206-1 and 206-2 on the other hand are partitioned into a number of sectors (i.e., sectors 212-1, . . . , 212-5), which are separated from one another by inter-sector gaps (i.e., inter-sector gaps 204-5, . . . , 204-8). Generally, each sector comprises, from left to right, a preamble field, a sync-mark field, a user-data field, and a data-pad field. The user-data field is reserved for writing a fixed amount of actual user data, such as 512 bytes, and is framed by a sync-mark field and a data-pad field. The sync-mark field is reserved for writing a sync mark, which is used by recording channel 108 to determine the beginning of actual user data. The data-pad field is reserved for writing a data pad, which is used by recording channel 108 to close out detection of the user data. The preamble field, which precedes the sync-mark field, is reserved for writing preamble data, which is used by recording channel 108 to perform zero-phase starts, timing acquisition, and gain acquisition to lock on the user data stored on the corresponding sector. The preamble data, sync mark, and data pad are written each time that user data is written to a particular sector or a fragment of a sector.
As shown in FIG. 5, first fixed-pattern field 206-1 of FIG. 2, is partitioned into two full sectors 212-1 and 212-2, a first half of sector 212-3, and two inter-sector gaps 204-5 and 204-6. First full sector 212-1 is flanked by inter-sector gaps 204-1 and 204-5, second full sector 212-2 is flanked by inter-sector gaps 204-5 and 204-6, and the first half of sector 212-3 is flanked by inter-sector gaps 204-6 and 204-2. Note that, while the first half of sector 212-3 is not a full sector, it still has a preamble field, sync-mark field, user-data field, and data-pad field. Second fixed-pattern field 206-1 of FIG. 2 is similarly partitioned into a second half of sector 212-3, two full sectors 212-4 and 212-5, and two inter-sector gaps 204-7 and 204-8. The second half of sector 212-3 is flanked by inter-sector gaps 204-3 and 204-7, fourth sector 212-4 is flanked by inter-sector gaps 204-7 and 204-8, and fifth sector 212-5 is flanked by inter-sector gaps 204-8 and 204-4. Similar to the first half of sector 212-3, the second half of sector 212-3 has a preamble field, sync-mark field, user-data field, and data-pad field. This formatting is repeated for the remainder of the track on which section 200 resides and is similar throughout the remainder of platter 124 (i.e., the remaining tracks). Tracks that are located closer to the center of platter 124 than section 200 may have smaller numbers of sectors due to their smaller circumferences, while tracks located farther from the center of platter 124 than section 200 may have larger numbers of sectors due to their larger circumferences. Further, depending on their circumferences, some tracks might not have sectors such as sector 212-3 that are split by a servo field.
FIG. 5 also shows the location of the three exemplary marginal defects of FIG. 2, relative to the subsequent drive formatting. First defect 210-1 is located in the sync-mark field of sector 212-2, second defect 210-2 is located in the user-data field of the first half of sector 212-3, and third defect 210-3 is located in the user-data field of sector 212-4. These defects may be tracked during the second defect-detection pass to determine whether they warrant being mapped out of the final usable storage space of platter 124.
FIG. 6 graphically illustrates a prior-art sequence 600 for writing a user data pattern to the first two and one-half sectors of section 200 shown in FIG. 5. At time t1, HD controller 104 enables the servo mode and performs a servo operation from times t1 to t2 to locate first servo field 202-1. After the servo mode is disabled, the write mode is enabled at time t3. The relatively brief delay from times t2 to t3 corresponds to write head 118 passing over inter-sector gap 204-1 without writing the user data pattern to the gap. Once the write mode is enabled, writing may be further delayed due to a delay in powering up preamplifier 112. Thus, as shown in close-up 602, although write mode is enabled at time t3, write head 118 might not begin writing the preamble until time t3a. The powering up of preamplifier 112 may be timed such that write head 118 begins writing the preamble as soon as inter-sector gap 204-1 has passed.
Once actual writing begins, write head 118 writes a preamble and sync mark, which are generated by recording channel 108, to sector 212-1. The preamble and sync marks are typically fixed patterns and are not usually encoded. After the sync mark has been written, the user data pattern is written to the user-data field of first sector 212-1 so that the user data pattern is in phase lock with the preamble and sync mark. The user data pattern, which is provided to recording channel 108 by HD controller 104 via NRZ bus 106, passes through the normal encoding path of recording channel 108 before it is written (e.g., the user data pattern undergoes encoding such as RLL encoding, error-correction encoding, or other suitable coding). At the end of the user-data field of first sector 212-1, a data pad is generated by recording channel 108 and written to the end of sector 212-1. Write mode is disabled at time t4; however, writing may continue for a brief period of time until the data pad is complete (i.e., at time t4a) as shown in close-up 604. Termination of the write mode may be planned such that the writing of the data pad is completed in time to leave inter-sector gap 204-5 between sectors 212-1 and 212-2. Note that, when jitter is present, a portion of the data pad could actually overwrite some or all of inter-sector gap 204-5. If jitter is not present, then nothing is written to inter-sector gap 204-5; however, inter-sector gap 204-5 could have a varying polarity or phase from a previous write operation (e.g., the first defect-detection pass) or have no signal at all. The effects of jitter and previous writes apply to all inter-sector gaps, not just inter-sector gap 204-5.
From times t5 to t8, full sector 212-2 and the first half of sector 212-3 are written in the same manner described above, without writing data to inter-sector gap 204-6. Once the first half of sector 212-3 has been written, the write mode is disabled at time t8 such that nothing is written to inter-sector gap 204-2. At time t9, the servo mode is enabled and a servo operation is performed to locate the next sectors for writing. The writing process described above is repeated for the remainder of sectors on the track in which section 200 resides. After the entire track has been written, the track is read back in a clockwise direction and analyzed by recording channel 108.
FIG. 7 graphically illustrates a prior-art sequence 700 for reading a user data pattern stored on the first two and one-half sectors of section 200 shown in FIG. 5. At time t1, HD controller 104 enables the servo mode and performs a servo operation from times t1 to t2 to locate first servo field 202-1. After the servo mode is disabled, the read mode is enabled at time t3. The relatively brief delay from times t2 to t3 corresponds to read head 120 passing over inter-sector gap 204-1 without reading the gap. Since inter-sector gap 204-1 is not read, it is also not analyzed for defects. Once the read mode is enabled, there is a lock period 208-1, as shown in close-up 702, in which recording channel 108 performs a zero-phase start, timing acquisition, and gain acquisition to lock on the preamble of sector 212-1.
Optimally, recording channel 108 would begin acquiring the lock at the beginning of the preamble. However, as shown in close-up 702 of FIG. 7, the read mode might not be enabled until after the beginning of the preamble has actually passed (i.e., read mode might be enabled at time t3 as opposed to time t2a). This relatively short delay between the beginning of the preamble and the enabling of the read mode may be introduced to ensure that recording channel 108 does not inadvertently attempt to perform the lock over inter-sector gap 204-1.
Once recording channel 108 has obtained a lock on the preamble of sector 212-1, recording channel 108 uses the sync mark to locate the beginning of the user data pattern and then begins reading and analyzing the user data pattern at time t3a. The signal recovered from platter 124 at this time (i.e., the user data pattern) is converted from analog to digital format and a data-integrity check is performed on the recovered signal by processing the signal through the decoding path of recording channel 108 (e.g., the recovered signal undergoes error-correction, RLL decoding, and other suitable decoding). The decoding path is capable of correcting some errors in the recovered signal that may occur as a result of, for example, defects in the magnetic recording material that is coated on the face of platter 124. To create some margin for further degradation of the magnetic recording material in the field, the error-correction capabilities of the decoding path are typically reduced intentionally. If errors are present after decoding, then sector 212-1 is flagged as defective and mapped out of the final usable drive storage space. If the user data pattern is correctly recovered, then sector 212-1 is not mapped out of the final usable drive storage space. Note that, as explained above, the preamble, sync mark, and data pad are not processed through the decoding path of recording channel 108. As a result, a data-integrity check is not performed for these areas, and consequently, these areas are not analyzed during the second pass.
At time t4, the reading mode is disabled, and just prior to this time, there is a close-out period 706 as shown in close-up 704 in which recording channel 108 uses the data pad to close out the reading operation. During close-out period 706, the data pad is not analyzed, and thus, this area is not checked for defects. After time t4, read head 120 passes over inter-sector gap 204-5, which is not read, nor analyzed for defects, assuming that the gap has not been overwritten due to jitter. As described above, inter-sector gap 204-5 could contain data that was recorded to the gap during a previous write. However, this data typically does not effect the reading operation since the user data pattern is framed by the sync mark and data pad.
From times t5 to t8, full sector 212-2 and the first half of sector 212-3 are read in the same manner described above, without reading inter-sector gap 204-6. Once the first half of sector 212-3 has been read, the read mode is disabled at time t8 such that inter-sector gap 204-2 is not read. At time t9, the servo mode is enabled, and a servo operation is performed to locate the next sectors for reading. The reading process described above is repeated for the remainder of sectors on the track in which section 200 resides. After the entire track has been read, the writing and reading operations of the second defect-detection pass are repeated on a track-by-track basis. The second pass is completed once all tracks on platter 124 have been analyzed for defects. After the second pass, further analysis may be performed on the flagged defects to further determine whether the flagged defects warrant mapping out of the final usable disk storage space.
The two-pass defect-detection method is relatively reliable for detecting defects during manufacturing. However, performing two passes may be relatively time consuming and costly to the manufacturer. To save time and cost, some manufactures have begun to use a single-pass method for detecting defects.
In general, the prior-art single-pass defect-detection method omits the first pass of the two-pass method which is performed using the non-final formatting shown in FIG. 2, and instead performs a single pass using the subsequent formatting shown in FIG. 5. The single pass is performed by (i) writing a real user data pattern to a track of platter 124 in a manner similar to that described above in relation to FIG. 6. The track is then read back in a manner similar to that described above in relation to FIG. 7, and the user data pattern is analyzed using both data-integrity and flaw-scan techniques. This is in contrast to the second pass of the two-pass method which analyzes the user data using only data-integrity techniques.
The flaw-scan techniques used in the prior-art single-pass method may be different from those described above in relation to the first pass of the prior-art two-pass method because the prior-art single-pass method analyzes a real user data pattern as opposed to a repetitive, fixed data pattern. As described above, the flaw-scan techniques used for the first pass exploit the recording channel's knowledge of the repetitive analog signal that is recovered when the fixed data pattern is read back from disk platter 124. Thus, the prior-art single-pass method may employ different techniques, such as windowing of the mean-squared-error, windowing of the gain error, and windowing of the phase error to analyze the analog signal that is recovered when a user data pattern, having encoding such as RLL and ECC encoding, is read back from disk platter 124.
In addition to performing both data-integrity and flaw-scan techniques, the prior-art single-pass method may analyze some areas of disk platter 124 that are not analyzed during the second pass of the prior-art two-pass method. As described above, the prior-art second pass does not analyze the preamble, sync mark, and data pad of each sector, or the inter-sector gaps that separate consecutive sectors such as inter-sector gaps 204-5, 204-6, 204-7, and 204-8. To minimize these gaps in defect-detection coverage, the prior-art single-pass method may provide some limited coverage over the preamble. For example, recording channel 108 may use gain and timing lock metrics generated during lock periods 208-1, 208-2, . . . , 208-6 to analyze these areas of the preambles. The ability of recording channel 108 to analyze these lock periods, however, is generally limited to these techniques, and thus, defect detection is not as reliable during the lock periods as it would be if other flaw-scan techniques could be used.