Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
  • G11B20/10—Digital recording or reproducing
  • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
  • G11B20/1816—Testing
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
  • G11B20/10—Digital recording or reproducing
  • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
  • G11B20/1879—Direct read-after-write methods
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
  • G11B20/10—Digital recording or reproducing
  • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
  • G11B20/1816—Testing
  • G11B2020/1823—Testing wherein a flag is set when errors are detected or qualified
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B2220/00—Record carriers by type
  • G11B2220/20—Disc-shaped record carriers

Definitions

• This invention relates generally to storage subsystems for computer systems.
• this invention relates to methods for detecting errors during write operations in disk drives, and differentiating between these errors and permanent media damage.
• the present invention is directed to a method of verifying the integrity of data written to a disk in a disk drive system, comprising: writing a first data section to a portion of the disk; periodically reading a pre-recorded signal from the disk; if the pre-recorded signal is substantially different from a predetermined value, reading the first data section written to the disk; and if the first data section read from the disk is substantially different from the first data section written to the disk, determining whether the portion of the disk is damaged.
• determining whether the portion of the disk is damaged comprises writing data on the portion of the disk, reading the data from the portion of the disk, and determining whether the read back data is valid.
• it is determined whether the first data section is recoverable and the data written on the portion of the disk comprises the first data section if the first data section is recoverable, and random data if the first data section is not recoverable.
• an error condition is generated if the read back data is valid and the first data section is not recoverable, and the data is reallocated to a second portion of the disk if the read back data is not valid.
• an error condition may be generated after reallocating the data if the first data section is not recoverable.
• the first data section comprises fewer than a predetermined number (e.g., 64) of blocks of data and whether the writing has completed, and, prior to periodically reading the pre-recorded signal from the disk, continuing the writing of the first data section if the first data section does not comprise fewer than 64 blocks of data and if the writing has not completed.
• a predetermined number e.g. 64
• Another exemplary method of verifying the integrity of data written to a disk in a disk drive system in accordance with the present invention comprises: receiving a write request to write a first data section to a portion of the disk; determining whether the first data section comprises fewer than 64 blocks of data; disabling a write cache if the first data section comprises fewer than 64 blocks of data; writing the first data section to a portion of the disk; periodically reading a pre-recorded signal from the disk; if the pre-recorded signal is substantially different from a predetermined value, reading the first data section written to the disk; and if the first data section read from the disk is substantially different from the first data section written to the disk, determining whether the portion of the disk is damaged.
• FIG. 1 is a diagram depicting an exemplary disk and arm assembly wherein the method of the present invention may be employed;
• FIG. 2 is a chart illustrating the relationship between head flying height and signal strength;
• FIG. 3 is a graphical representation of an exemplary signal of a portion of data from the disk;
• FIG. 4 is a graphical representation of the exemplary signal showing signal degradation in a track section caused by increased flying height;
• FIG. 5 is a graphical representation of the effect of flying height on reading and writing data
• FIGS. 6 A and 6B are flow charts representing an exemplary method in accordance with the present invention.
• FIG. 7 is a flow chart representing another exemplary method in accordance with the present invention.
• FIGS. 8A, 8B, and 8C are flow charts representing another exemplary method in accordance with the present invention.
• FIG. 1 is a representation of a disk drive mechanism wherein the operation of the present invention may be illustrated.
• a disk 12 rotates about a spindle motor axis 14.
• the surface of the disk 12 is receptive to electromagnetic signals for storing data.
• Read/write electronics, embedded within slider bearing 16 generates an electromagnetic signal to write data and read an electromagnetic signal from the disk surface to read data.
• the slider bearing 16 with embedded read/write electronics is also referred to herein as a read/write head 16.
• the read/write head 16 is attached to arm 18.
• the head 16 and arm 18 assembly are attached to suspension 20. To access selected data sections, the arm 18 with attached read/write head 16 moves over the surface of disk 12 both reading and writing data as required.
• FIG. 2 is a graph of the normalized strength of the electromagnetic signal on the disk surface versus the flying height of the read/write head 16. Line 22 plots the relationship between these two variables. Significantly, there is an inverse relationship between the two variables. Thus, increases in flying height correspond to decreases in normalized signal strength.
• the flying height between the read/write head 16 and the surface of disk 12 reaches approximately between 0.04 and 0.1 ⁇ m, depending on the disk drive system, for a properly functioning full spinning disk 12. As illustrated in FIG. 2 by line 22, such a flying height corresponds to approximately 80 percent of the normalized signal strength.
• the flying height increase is transient, the data section can be re-read and the data recovered. In other words, the signal on the surface of the disk 12 was written properly, but a transient increase in flying height caused the read/write head 16 to deviate too far from the surface to properly read the data.
• the flying height exceeds 0.4 ⁇ m the signal strength rapidly diminishes to zero.
• the format divides the surface of the disk 12 into tracks and subdivides those tracks into sectors.
• the surface of disk 12 is divided into tracks by pre-recording servo marks along each track. For example, there may sixty or more servo marks per track, i.e., a servo mark every six degrees.
• the read/write head 16 uses these servo marks during operation of the disk drive to locate tracks. Thereafter, the read/write head 16 can lock onto tracks by following the servo marks.
• the track is subdivided into sectors.
• each sector 33 is demarcated along the track with a header 36 and a trailer 38 that is recorded onto the disk surface.
• the header contains overhead information, such as constant density recording ("cdr") field (indicating how many bytes to the next servo field), track id field (identifying all sectors on the same logical track), sector id field (identifying a particular sector) and id error correction code field (containing an error correction code for cdr, track id and sector id fields).
• the number of sectors per track may vary, e.g., the innermost track may have 90 sectors per track, while the outermost track has 150 sectors per track. However, the number of servo fields remains the same for each track. For example, servo marks may appear every 3 degrees around each track. Servo marks contain a grey code (containing the physical track number), and norm and quad fields (indicating the head distance from the track center).
• the disk 12 After the disk 12 has been properly formatted, it is ready for use, such that data may be read from and written to its surface in data sections within each sector. While the read/write head 16 is reading and writing data to the disk 12, the arm 18 must follow the tracks that were written to the surface of the disk 12 during formatting. The arm 18 via the head 16 thus reads the servo marks to ensure that the tracks are closely followed during operation. Significantly, during a write operation, the head 16 continues to read the servo marks to ensure proper track following and to read the sector identifiers to find the proper location for data. Additionally, during the write operation, the head continues to read every grey code, servo mark, id mark, cdr field and track id. The signal read back will translate to a specific predetermined value. If any of the values do not match the predetermined value, an error condition results. Also, certain values are checked against the error correction code field. If a mismatch occurs, then an attempt is made to correct the data using the error correction code field.
• the norm and quad fields of the servo marks are checked against a predetermined amplitude. If a mismatch occurs, a position error will be reported indicating how far the heads are from the center of the track.
• transient changes in head flying height during writes to disk 12 could result in a permanent signal loss. That is, as the flying height increases, the signal recorded on the media decreases. Thus, if the flying height crosses a threshold point, which may vary based on such factors as recording media and head type, the signal would not be recoverable on subsequent read operations. Unfortunately in such a case, the error may not be discovered until much later and permanent data loss could result.
• a feature of the present invention detects and corrects write errors caused by transient increases in flying height with a minimal impact on drive performance. This feature exploits the need for the drive to continue to read information, such as servo marks, from the disk 12 even during write operations. Therefore, flying height increases that persist while the read/write head is flying above portions of the disk 12 having pre-recorded signals, such as a servo mark, are detected and corrected. In particular, because some information, such as servo marks, was written and verified prior to the use of the disk 12, read signal degradation detected during track following and sector seeking likely resulted from flying height increases. In accordance with one aspect of the present invention, the data previously written is re-read and verified. As a result, a high quality write operation can be performed while only verifying a minimal amount of data.
• FIGS. 3 and 4 graphically present linear representations of track sections 30 from the disk 12. It should be noted that signal strength has been graphed along the y axis and time has been graphed along the x axis.
• data sections 32a, 32b were written normally, i.e., while no changes in flying height were experienced.
• the pre-recorded signals such as the servo mark 34, the sector headers 36a, 36b and the sector trailer 38 have substantially the same signal strength as the data sections recorded during subsequent write operations.
• FIG. 4 presents a similar track section 30 written while experiencing a change in flying height. By comparison to the signal strength depicted in FIG.
• the signal strength degrades in the data sections 32a, 32b of FIG. 4. That signal weakness corresponds to an increase in head flying height during the write operation.
• the pre-recorded information such as servo marks 34 and sector headers 36a, 36b remain at pre-recorded signal levels.
• the data recorded therein will likely be unreadable and unrecoverable if it remains uncorrected.
• the read/write head 16 by testing the strength of the prerecorded signal, e.g., servo marks 34 and sector identifiers (embedded within sector headers 36) while writing to the data sections 32, transient changes in flying height can be detected.
• the pre-recorded signals 34, 36, and 38 remain at pre-recorded signal strength, a read of those signals during the increase in flying height would likely result in diminished signal strength and read errors.
• the read/write head 16 while data is written to the disk 12, the read/write head 16 must constantly determine its current location. As noted above, this determination is conventionally performed by reading servo marks 34 and sector identifiers.
• the present invention detects transient write errors based on difficulty in reading pre-recorded information on the disk such as servo marks, ID marks, etc. In the event of such difficulty, the drive will automatically read the data it just wrote. If errors were encountered during this write process, the drive will either rewrite the data or report errors to the host system which will in most cases issue a rewrite operation.
• the present invention also distinguishes between transient errors and permanent media damage and reallocates permanent disk damages to prevent further loss.
• the process begins with a request to write a block of data to the disk 12, starting at a particular track and sector location (step 100).
• an error flag is initialized to zero (step 102). This flag is used, as will be further described below, to indicate whether a potential write error has occurred.
• the arm 18 moves the head 16 to the proper track by seeking to and following the servo marks.
• a servo mark is read (step 104). According to an aspect of the present invention, if the flying height of the head 16 is too high an error will occur during the read of the servo mark.
• the servo mark read is tested (step 106). If an error occurred during that read of the servo mark (step 104), the error flag is set. If, on the other hand, no error occurred, the process continues.
• the head scans the track for the proper sector to receive the data. Accordingly, the sector identifier is read (step 110). Any errors occurring during the read of the sector identifier result in the setting of the error flag. As with the servo mark read, excessive flying height during the read of the sector identifier will also result in a read error. Thus, the read of the sector identifier is tested for errors (step 112). If the read of the sector identifier resulted in an error, the error flag is set (step 114).
• the data is written to the data section of the sector (step 116) (i.e., assuming the error is recoverable via an error correction code). If the write is not complete, i.e., more data remains to be written to different sectors, the process continues (steps 118, 120). Otherwise, the write is complete and the error flag is checked (steps 1 18, 122). If no read error occurred, the operation is complete. However, if the error flag is set indicating a read error, all the data previously written during this write request is read back for verification (step 124). At step 126, it is determined whether the data that was read back is valid or if there is an error. If the data is valid, processing ends at step 190. However, if a data error is indicated at step 126, an attempt is made to recover and rewrite the data and processing continues at step 140.
• step 140 it is determined if the data in the faulty sector is available for recovery. If the data is available, another error flag (referred to as flag 1 ) is set to 0 at step 142, and the data is rewritten on the same location on the disk at step 144. The data is read back at step 150, and it is determined at step 152 if the data is valid. If the data is valid, it is determined that the error was transient, the media is not damaged at this location, and processing ends at step 190. If the data is not valid at step 152, then it is determined that the media is damaged at this sector location, and another sector is chosen to write the data to at step 154, and the data is rewritten at the newly chosen sector. Processing then ends at step 190.
• flag 1 another error flag
• step 156 an error is reported at step 156 that indicates there is a media defect, and processing ends.
• the drive will write random data to the sectors with invalid data. Otherwise, the drive will rewrite the data. The drive then performs a read operation to verify the data written. If the data is invalid, then the new sectors are determined to be bad and get reallocated. An attempt will be made to write data at the new locations. If the data is valid, the sectors will be deemed to be good, and the errors are deemed to be transient. The process will either end or the drive will report an error to the host if random data was used during the write.
• a write-behind cache can be used as a form of temporary storage in which data is held or cached for a short time in memory before being written on the disk. This caching is implemented to improve system performance by reducing the number of times the system goes through the process of reading from and writing to the disk.
• One embodiment of the present invention avoids the increased risk of having to report a deferred write error to the host when a write-behind cache is being used.
• the write-behind cache functions as usual unless a verify pass (steps 140- 156 in FIG. 6B) occurs. If this happens, in accordance with the present invention, the write-behind cache is shut down until the next command.
• the method described with respect to FIGS. 6 A and 6B functions as described above except it is disabled during the time between when the write-behind cache reports good completion status to the host and the time in which the rest of the data blocks belonging to the write command that are still in the buffer are transferred to the media.
• FIG. 7 A flow chart of one exemplary method of the above embodiment in which data is written from a buffer to the disk is shown in FIG. 7. The method is similar to that shown in FIG. 6 A, except steps 119 and 121 have been added. At step 119, after the write is completed, it is determined if there are fewer than the predetermined number (e.g., 64) of blocks of data being transferred. If so, then processing continues at step 122.
• a predetermined number of blocks of data for example, 64 blocks of data.
• step 121 If more than 64 blocks of data are being transferred, then it is determined at step 121 if the status has been reported to the host. If not, then processing continues at step 122; otherwise, the next write request is obtained at step 100. Moreover, if the error flag in step 122 is not set, then the next write request is obtained at step 100.
• a write request is received to write a block of data to the disk, starting at a particular track and sector location.
• it is determined if the write request is sequential i.e., whether the write request is at the next location on the disk relative to the previous write. If the write request is sequential, processing continues at step 220, as described below. If the write request is not sequential, the write -behind cache is shut down at step 210. This stops the disk transfer routine (see FIG. 8B).
• verification steps 140-156 in FIG. 6B is enabled.
• step 220 it is determined if fewer than a predetermined number of blocks of data (e.g., 64) have been moved. This optional step is used to limit exposure to transient write errors. If fewer than blocks have been moved, the write-behind cache is shut down at step 225, and the write-behind cache is disabled for the current write request, at step 230. Processing continues at step 102 in FIG. 6A.
• a predetermined number of blocks of data e.g. 64
• step 240 it is determined whether the host transfer to the buffer is complete (similar to step 121 in FIG. 7). If not, then the system waits until the host transfer has completed (steps 240, 245). After the host transfer is complete, it is determined at step 250 if the error flag is set (similar to step 122 in FIG. 7). If the error flag is set, then the system waits for the disk transfer routine (FIG. 8B) to complete (similar to step 124 in FIG. 7). Processing continues with steps 118- 190 of FIGS.6A and 6B being executed.
• a counter is set at step 255 to count the number of blocks of the buffer that are left to be moved to the disk (from the disk transfer routine in FIG. 8B).
• the verification process is disabled at step 260, and processing continues with steps 118- 190 of FIGS. 6 A and 6B being executed.
• FIG. 8B is a flow chart of an exemplary disk transfer method in accordance with the present invention.
• the disk transfer method is called at step 270. It is determined at step 272 if a soft write error has occurred. If not, then processing continues. If a soft write error has occurred, then an error flag is set at step 274, and the write-behind cache is shut down at step 276. Disk transfer continues until all of the data in the buffer has been moved to the disk.
• step 282 it is determined if the block of data has been successfully transferred to the disk, and at step 284 it is determined if the verification process has been disabled. If either of these events has not occurred, processing continues at step 200 in FIG. 8 A. If both of the events have occurred, then the counter of step 255 in FIG. 8 A is decremented at step 286, and compared to zero at step 288. If the counter equals zero, the verification process of FIG. 6B is enabled. In either event, processing continues at step 200.
• the description given herein with respect to those figures is for exemplary purposes only and is not intended in any way to limit the scope of the invention.

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• 2000
  • 2000-09-21 JP JP2001530858A patent/JP2003511813A/ja active Pending
  • 2000-09-21 WO PCT/US2000/025889 patent/WO2001027924A1/en not_active Application Discontinuation
  • 2000-09-21 EP EP00965249A patent/EP1149380A1/de not_active Withdrawn
  • 2000-09-21 AU AU75993/00A patent/AU7599300A/en not_active Abandoned
  • 2000-09-21 KR KR1020017007122A patent/KR20010101145A/ko not_active Application Discontinuation
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