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
  • G11B20/1883—Methods for assignment of alternate areas for defective areas
• • 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
  • G11B20/1833—Error detection or correction; Testing, e.g. of drop-outs by adding special lists or symbols to the coded information
• • 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
  • G11B2220/00—Record carriers by type
  • G11B2220/90—Tape-like record carriers

Definitions

• the present invention pertains generally to data recording/recovery devices, and more particularly to a method for rewriting data that fails a check-after-write test to ensure data integrity.
• Data storage devices which are used in both short- and long-term capacities, are an integral part of modern computer systems. While factors such as costs, device form factor, storage media size and capacity, and recording and recovery times are of high importance, of primary concern is the ability to maintain data integrity.
• many tape drives include a check-after-write scheme whereby data is verified by a read head as the data is recorded onto the tape.
• a check-after-write scheme whereby data is verified by a read head as the data is recorded onto the tape.
• the newly recorded data is verified half a drum rotation later by a pair of alternate azimuth read heads located 180 degrees relative to the pair of write heads.
• the backhitching sequence can be avoided by simply rewriting tracks that contain "bad" data further down the tape without stopping the process.
• this methodology has the disadvantage that if the rewrite count is high, a significant portion of the tape is occupied by duplicate tracks containing mainly redundant "good” data, thereby reducing the storage capacity of the tape.
• the present invention is a novel method and apparatus for performing rewrites at the packet level by allowing data to be recorded onto tracks on a magnetic media in any address sequence.
• Local packet address information is included in the track packet itself to allow track packets to be written to the storage medium in any addressing order. This allows a single packet to be rewritten along a later track among other track packets that are being recorded for the first time, thereby reducing rewrite track overhead and eliminating the requirement for a lengthy backhitching sequence.
• FIG. 1 is a system diagram of a data recording/recovery device in which the invention operates
• FIG. 2 is a diagram illustrating a control packet
• FIG. 3 is an illustrative embodiment of a local packet address (LPA) in accordance with the invention
• FIG. 4(a) is a diagram illustrating the relationship between a global segment address and a local packet address
• FIG. 4(b) is a diagram illustrating the relationship between the global segment address, local packet address, and physical segments on a storage medium
• FIG. 5 is a diagram illustrating one embodiment of the contents and organization of a segment of a multi-segment data buffer implemented in accordance with the invention
• FIG. 6(a) is a diagram of a data packet completely filled with user data
• FIG. 6(b) is a diagram of a data packet filled partially with user data and padded with fill data
• FIGS. 7(a) - 7(d) illustrate one embodiment of key overhead packet
• FIG. 8 is a diagram illustrating one embodiment of the contents and organization of a packet status table corresponding to the segment of FIG. 5;
• FIG. 9 is a flowchart illustrating one embodiment of a method for performing rewrites of bad packets in accordance with the invention.
• a technique for rewriting data that fails a check-after-write test in a data recording/recovery device without requiring a backhitching sequence or the overhead of rewriting entire tracks is described in detail hereinafter.
• the invention is described in the context of a magnetic tape drive; however, the method of the invention may be employed in any recording/recovery device that writes data in tracks onto the storage medium.
• FIG. 1 is an illustrative embodiment of a data storage system in which the present invention operates.
• user data 3 is typically transferred to and from a recording/recovery device 4 by a host system 2 in variable length logical block sets 3.
• Each logical block set (LBS) 3 is a collection of user data bytes that contain a variable number of logical blocks (LBO, LB1 , ..., LBN).
• Each logical block (LB) is defined within its LBS by a unique logical block address (LBA).
• LBS data 3 is partitioned into a number of fixed-sized data packets 30 by a data buffer manager 6 and placed within a buffer packet 15 in a data buffer 10 until being transferred to the storage medium 50.
• write logic manager 18 causes packet CRC generator 20 to generate a packet cyclical redundancy code (CRC) over the packet and packet ECC generator 22 to generate a packet ECC over the packet and packet CRC.
• CRC packet cyclical redundancy code
• ECC generator 22 to generate a packet ECC over the packet and packet CRC.
• Write logic manager 18 formats the packet, packet CRC, and packet ECC, a logical packet address (LPA), and framing information into a track packet 7.
• the LPA comprises the address of the location of the packet in the segment 11.
• each track packet 7 is a fixed size and includes framing information 72, a local packet address field 74, a packet field 76, a packet CRC field 78, and a packet ECC field 80.
• a packet frame synchronizer 34 uses the framing information 72 to detect the leading edge of a track packet 7.
• Framing information 72 is a unique signal that is sent between track packets 7 in the channel domain to provide synchronization for track packet detection. This signal does not obey the run-length restriction of the channel modulation code and does not have a byte symbol associated with it, meaning that it is not decoded to a byte symbol by demodulator/decoder 36.
• the packet framing signal is 16 bit cells long and is a 4, 8, 4 pattern.
• a demodulator/decoder 36 demodulates and decodes the packet 7.
• a read logic manager uses the local packet address field 74 to first determine whether the track packet 7 contains a control packet. The handling of control packets is performed by control packet processor 42 (discussed hereinafter). If the track packet 17 does not contain a control packet, it contains either a data packet 30, an overhead packet 32, or a segment ECC packet 34. Read logic manager 38 uses the local packet address 74 along with the current global segment address (discussed hereinafter with respect to control packets) to determine the correct location of the track packet in the buffer 10. Read logic manager 38, in conjunction with packet CRC generator/error detector 20, uses the packet CRC field 78 to detect whether track packet 7 contains any errors.
• Control packets 36 are generated during a recording session by a control packet processor 42, and contain information relating to the position of the media (such as beginning- or end-of-media), the beginning and or ending of files or data (e.g., filemarks, tapemarks, end-of-data marks), global address information (e.g., the global segment address of data surrounding the control packet), and system information (such as device control code).
• control packets 36 are processed by control packet processor 42 to determine the position of the storage media and where to place recovered data packets, buffer overhead packets, and segment ECC packets in the data buffer.
• Certain control packets are periodically placed along the tracks 9 of the storage medium 50 and contain a global segment address (GSA) 37.
• Control packet processor 42 extracts the global segment address 37 from these control packets 36 and maintains the current global segment address 37 in local storage.
• the GSA 37 is used in concert with a local packet address (LPA) contained in the LPA field 74 of each track packet 7 to define the location of a packet in a segment 11 of the buffer 10.
• FIG. 3 is a diagram illustrating one embodiment of the definition of LPA field 74 in accordance with the invention.
• the LPA field 74 is a two-byte field that indicates whether the packet is a data/overhead/ECC packet 30, 32, 34 or a control packet 36.
• the LPA field 74 contains the buffer segment 11 address for the packet. As illustrated, if the track packet 7 contains a data/overhead packet 30/32, the segment address is defined in bits 13:11 , the row address is defined in bits 10:6, and the column address is defined in bits 5:1. Bit 0 indicates whether the packet is a rewritten packet. The locations of the row, column, diagonal and special ECC packets 34 are defined as illustrated. If the track packet 7 contains a control packet 36, bits 5:1 contain a type definition.
• the lower 5 bits of the current GSA are shared by the upper 5 bits of the local packet address (LPA) field 74 of a track packet.
• the upper two bits 15:14 of the LPA allow for a four-segment aliasing, as illustrated in FIG. 4(a). In other words, the tape must physically move the equivalent of four memory buffers before LPAs begin to repeat.
• the global segment address (GSA) 37 addresses each segment 1 1 boundary in the data buffer 10 which corresponds to a physical segment 52 on tape 50, as shown in FIG. 4(b).
• the data buffer 10 comprises six buffer segments 11.
• the GSA 37 is a 24-bit number that spans an address range of 2 24 segments 11 , which covers the entire span of the storage media 50.
• the LPA allows data overhead/ECC packets 30, 32, 34 to be located unambiguously in the correct buffer segment 11 within four complete buffers 10 (of six segments 11 each).
• the two-byte LPA field 74 is combined with the 3- byte GSA 37 from an associated control packet 36 to uniquely identifies every data/overhead/ECC packet 30, 32, 34 location in a tape volume.
• the write logic never allows local packet address 74 numbers spanning more than six segments 11 to exist on tape 50 within the same track 9.
• the local packet address (LPA) 74 must be initialized at the start of a write session. Starting points for write sessions must initialize the LPA 74 to the starting address of a buffer segment 11. For initializing a tape partition, the hardware in the illustrative embodiment uses a value of zero for the initial value. Subsequent write sessions always involve a splicing operation that first read what the last LPA 74 used was. The new write data after the splice point then uses the next address that starts the next buffer segment 11.
• this addressing scheme namely the inclusion of a local packet address in each packet and the availability of an associated global segment address periodically written nearby its associated packets, provides a method for unambiguously indicating the correct location of a packet in a segment 11 of the data buffer 10.
• FIG. 5 illustrates one embodiment of the contents and organization of a segment 11 of a multi-segment data buffer 10 implemented in accordance with the invention.
• segment 11 comprises a set of fixed- size buffer packets 15, each belonging to either a data/overhead area 104 or a segment ECC area 106.
• the data/overhead area 104 comprises 114 packets 15 of 64 bytes each, and arranged in a 32- by-32 array. Packets 15 in the data/overhead area 104 contain either data packets 30 or overhead packets 32.
• Overhead packets 32 are used to locate the positions of where the LBS's 3 start and end in the segment 1 1.
• a packet 15 residing in the data/overhead area 104 of segment 11 contains either a data packet 30 or a overhead packet 32.
• Each data packet 30 is either completely filled with LBS data, as illustrated in FIG. 6(a) or contains LBS data followed by "fill" data, as illustrated in FIG. 6(b).
• the last data packet 30 of a given LBS 3 is padded out with don't-care "fill" data. Every LBS 3 begins at the beginning of a data packet 30 boundary, and each data packet 30 contains no more than one LBS.
• Data/overhead area 104 of segment 11 also contains at least one overhead packet 32.
• Overhead packets 32 contain overhead information about the LBS's 3 that are stored in the segment 11. This information includes the location of all junctions between LBS's 3 residing in the segment 11 , the logical block address (LBA) of the first LBS 3 to start in the segment 11 , the size and number of logical blocks (LB's) within each LBS 3 that starts in the segment 11 , the tape partition, volume initialization count, compression mode indicator, segment flush indicator, and the segment CRC.
• LBA logical block address
• LB's logical blocks
• the number of overhead packets 32 in a given segment 11 is variable and depends on the number of LBS's that reside in the same segment.
• the variable overhead scheme optimizes the segment overhead space used.
• Each segment 11 contains at least one overhead packet 32, called the key overhead packet 32.
• the key overhead packet 32 always occupies the last packet location of the segment (in the illustrative embodiment, row 31 , column 31 ). If there are less than seven LBS junctions within the segment 11 , the key overhead packet 32 is the only overhead packet 32 in the segment 11 and the LBS data can occupy up to the next to last packet location (row 31 , column 30).
• FIG. 7(a) illustrates one embodiment of key overhead packet 32.
• key overhead packet 32 occupies 64 bytes, comprising nine separate fields. These fields include a main key field 202, the segment CRC field 204, a first LBS attributes field 206, and six LBS boundary fields 208a-208f. Each field 202, 204, 206, and 208a-208f include an 8-bit CRC associated with them for error detection across their field.
• FIG. 7(b) illustrates one embodiment of the main key field 202 in key overhead packet 32.
• Main key field 202 occupies four bytes including one unused byte 210, a segment key 212, the location of the last LBS boundary 214, and the main key field CRC 216.
• the segment key 212 include bits SKIP, SYS DATA, LBS ENDED,
• LBS STARTED and FLUSH which are used for conveying key information about the LBS's that are stored in the segment 11.
• the last used overhead packet 32 is adjacent to the last data packet 30 in the segment 11 , except for when the segment 1 1 is flushed or when a single unused packet 15 is skipped.
• SKIP bit is set to indicate the latter case.
• SYS DATA is set to indicate that the LBS data in this segment 1 1 is not user logical block data but rather system data. System data may include data created by the drive used to store control information such as locations of filemarks, directory structure, and logical format information as controlled by software.
• LBS ENDED bit is set only when at least one LBS 3 has an endpoint residing in this segment 11.
• LBS STARTED bit is set only when at least one LBS 3 has a starting point in this segment 11.
• FLUSH bit is set to indicate that the segment 11 has been flushed, as described hereinafter.
• the main key field 202 also includes a last LBS boundary field location 214. This is an 8-bit value which locates the last LBS boundary field location within the overhead area of the segment 11. Five bits are used to indicate which column of row 31 the overhead packet 32 that contains this field is located. The remaining three bits are intra- packet (IPK) bits used to specify one of eight starting addresses within the 64-byte data packet where the last LBS boundary field begins.
• the main key field 202 includes an 8-bit CRC field 216 which is used to store the CRC calculated across the main key field 202.
• the CRC polynomial is: X[8] + X[7] + X[2] + X[0].
• Key overhead packet 200 in FIG. 7(a) also includes a segment CRC field 204.
• segment CRC 204 is a 4-byte CRC used for storing the segment post-correction error detection, and is discussed hereinafter.
• Key overhead packet 32 may also include one and up to six LBS boundary fields 208a-308f.
• FIG. 7(d) illustrates one embodiment of the format of an LBS boundary field 208, including a logical block size field 230, a number of logical blocks per LBS field 232, a logical block compression mode (LBSC) indicator 234, an LBS endpoint location 236, 238, 240, a skip indicator 242, a flush indicator 244, an endpoint valid indicator 246, and an LBS boundary field CRC 248.
• Logical block size field 230 occupies 18 bits in the illustrative embodiment and specifies the size of the logical blocks (LB) 104 stored within the logical block set (LBS) 3.
• the number of logical blocks per LBS field 232 occupies 13 bits and specifies how many LB's 104 are stored within the LBS 3.
• the logical block compression mode (LBSC) indicator 234 is set only when the LBS 3 has been compressed by compression hardware 116.
• the location of a valid LBS endpoint is determined using a 6-bit LBS endpoint byte field 236, a 5-bit LBS endpoint column field 238, and a 5-bit LBS endpoint row field 240, in combination with endpoint validity indicator VALID END 246. Only if the VALID END indicator 246 is set is the endpoint location valid.
• An example of a valid LBS boundary field 208 having an invalid endpoint would be for an LBS 3 that started in this segment 11 but ended in the next segment.
• LBS boundary field CRC 248 contains the CRC calculated over the entire 8-byte LBS boundary field 208, using the polynomial: X[8] + X[7] + X[2] + X[0].
• LBS boundary fields 208a-308f are valid in a given overhead packet 32.
• the main key field 202 in the overhead packet 32 points to the last valid LBS boundary field 208 within the overhead packet 32. Also, if an LBS 3 starts in a segment 11 but does not end in the same segment 11 , the last four bytes of the endpoint are not valid, but the first four bytes are valid.
• the FIRST VALID bit in the segment key field 212 in the main key field 202 of the key overhead packet 32 indicates that the first LBS that starts in the segment starts in the very first location of the segment (e.g., address 0). Referring back to FIG. 5, segment 11 comprises a set of packets 15 organized into a segment ECC area 106.
• each buffer segment 1 1 utilizes a 32-bit (4-byte) CRC for error detection and a multiple-layer Reed-Solomon scheme for error correction.
• a 32-bit CRC used for segment post-correction error detection is stored in the segment CRC field 204 of the segment key overhead packet 32.
• All of the data packets 30 residing in the segment data/overhead area 104 of a segment 11 are divided by a CRC generator polynomial implemented in the CRC generator 14 to produce the 4-byte CRC.
• the last data packet 30 of the segment 11 (which may contain fill data if an LBS ends in it) is always used as a complete segment in this calculation.
• Multi-layer redundancy is provided by pairs P and Q of redundant codes generated over a plurality of patterns of packets 15 of a segment 11 of buffer 10.
• the plurality of patterns include rows, columns, and diagonals. Other patterns may be used.
• error correction is performed over all of the first redundant codes P for both row and column ECC codes, and all of the second redundant codes Q for both row and column ECC codes to generate special ECC codes 158.
• Segment ECC generator 16 includes a Reed-Solomon Syndrome generator and correction circuit that provides for a one- or two-packet correction in any row, column, or diagonal of the data/overhead area 104 of segment 11 by using erasure pointers.
• column redundancy is provided by column ECC packets P 154 and Q 155 for each column (0 through 31 ) of data/overhead area 104 of buffer segment 11.
• the entire 32-packet-by- 32-packet data/overhead area 104 of the buffer segment 11 is used to generate column ECC redundancy.
• Each of the 32 columns of packets 30 in the data/overhead area 104 is used to generate two unique redundant codes in column ECC packets P 154 and Q 155.
• Diagonal redundancy is provided by diagonal ECC packets P 156 and Q 156 for each diagonal (0 through 31) of data/overhead area 104 of buffer segment 11.
• the diagonals are defined to each include 32 packets.
• a given diagonal N starts at column 0 and row N, and the next element of the diagonal is found by incrementing both the current column number and current row number, modulo 32.
• Table 1 illustrates the calculation of the diagonals for this embodiment.

Landscapes

• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Signal Processing For Digital Recording And Reproducing (AREA)
• Information Retrieval, Db Structures And Fs Structures Therefor (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (2)

Family

ID=22642630

Family Applications (1)

Country Status (7)

Cited By (2)

Families Citing this family (16)

Citations (3)

Family Cites Families (96)

• 1998
  • 1998-10-20 US US09/176,015 patent/US6381706B1/en not_active Expired - Fee Related
• 1999
  • 1999-10-20 WO PCT/US1999/024665 patent/WO2000023998A1/en not_active Ceased
  • 1999-10-20 EP EP99955115A patent/EP1125295B1/en not_active Expired - Lifetime
  • 1999-10-20 DE DE69933938T patent/DE69933938T2/de not_active Expired - Fee Related
  • 1999-10-20 JP JP2000577662A patent/JP2002528839A/ja active Pending
  • 1999-10-20 AU AU11292/00A patent/AU1129200A/en not_active Abandoned
  • 1999-10-20 AT AT99955115T patent/ATE344961T1/de not_active IP Right Cessation

Patent Citations (3)

Also Published As

Similar Documents

Legal Events