Reconstructive error recovery procedure (ERP) using reserved buffer

• US 9,053,748 B2
• Filed: 11/14/2012
• Issued: 06/09/2015
• Est. Priority Date: 11/14/2012
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Katagiri, Takashi, Nylander-Hill, Pamela R.
• Primary Examiner(s): Decady, Albert
• Assistant Examiner(s): KABIR, ENAMUL MD
• Application Number:
  US13/676,477
• Publication Number:
  US 20140136918A1
• Time in Patent Office: 937 Days
• US Class Current: 1/1
• CPC Class Codes: G11B 20/1833 by adding special lists or symbols to the coded information G11B20/1806, G11B20/1866 take precedence
• CPC Class Codes: G11B 2020/1853 using a product code which has inner and outer parity symbols
• CPC Class Codes: H03M 13/2906 using block codes H03M13/2957 takes precedence
• CPC Class Codes: H03M 13/2909 Product codes
• CPC Class Codes: H03M 13/293 with erasure setting
• CPC Class Codes: H03M 13/3715 Adaptation to the number of estimated errors or to the channel state

Abstract

According to one embodiment, a method for reading data from a medium includes reading a data set from a medium repeatedly using different settings until either: a reconstructed data set is sent to a host and/or stored, or a maximum number of rereads has been reached, after each reading of the data set, storing each row to the reserved data buffer that has no errors or errors in the row are correctable using C1-Error Correction Code (ECC) unless a matching row already exists in the reserved data buffer that has fewer corrected errors therein, assembling the data set from the rows stored in the reserved data buffer to form an assembled data set, correcting any remaining errors in the assembled data set using C2-ECC to form the reconstructed data set, and sending the reconstructed data set to the host and/or storing the reconstructed data set.

Claims

1. A system for reading data, the system comprising:

logic configured to set a first counter to zero prior to reading a data set;

logic configured to read the data set one or more times, the data set comprising a plurality of portions which combine together to wholly form the data set, wherein during each read of the data set, settings are changed in an attempt to better read the data set and the first counter is incremented by one;

logic configured to store all portions of the data set to a reserved data buffer after a first reading of the data set;

logic configured to determine whether the stored data set is correctable using at least one of C1-error correction code (ECC) and C2-ECC, wherein when the data set is correctable using at least one of C1-ECC and C2-ECC, the stored data set is recovered;

logic configured to determine whether the first counter equals a predetermined threshold prior to each read of the data set, wherein when the first counter equals the predetermined threshold the data set is reported as unreadable;

logic configured to set a second counter to zero prior to rereading the data set;

logic configured to reread portions assumed to be in the data set;

logic configured to perform a validity check to determine whether a currently read portion is in the data set;

logic configured to determine that the currently read portion of the data set is correctable using C1-ECC using a syndrome check when the validity check confirms that the portion is from the data set;

logic configured to store one or more of the portions of the data set to the reserved data buffer after subsequent readings of the data set when the one or more portions are correctable using C1-ECC;

logic configured to determine that all portions of the data set have been reread according to the second counter, wherein the second counter is incremented by one after any of;

storing a portion of the data set, determining that the currently read portion is not in the data set, and determining that the currently read portion of the data set is not correctable using C1-ECC;

logic configured to aggregate the one or more portions of the data set in the reserved data buffer to form an assembled data set, wherein each of the one or more portions are correctable using C1-ECC;

logic configured to determine whether C2-ECC is capable of correcting all errors in the assembled data set;

logic configured to correct any remaining errors in the assembled data set using C2-ECC to form a reconstructed data set and send the reconstructed data set to a host when C2-ECC is capable of correcting all errors in the assembled data set; and

logic configured to reread the data set using a different setting in an error recovery procedure (ERP) when an error in the assembled data set, is not correctable using C2-ECC.

2. The system as recited in claim 1, wherein the plurality of portions of the data set are C1-encoded rows in an array representing the data set.

3. The system as recited in claim 1, wherein when a portion already exists in the reserved data buffer, the existing portion is overwritten when a corresponding portion from the one or more portions that are correctable using C1-ECC has fewer corrected errors therein than the existing portion.

4. The system as recited in claim 1, wherein when the data set is reread, existing portions in the reserved data, buffer are overwritten with portions having fewer errors corrected therein, and it is determined whether C2-ECC is capable of correcting all errors in the assembled data set until either the reconstructed data set is sent to the host, or a number of allowable retries is reached as indicated by the counter and the data set is reported to the host as unreadable.

5. The system as recited claim 1, wherein the data set is read from a magnetic tape.

6. The system as recited in claim 5, wherein different settings comprise a change to at least one of:

a tape speed during reading and a data flow correction power.

7. A method for reading data, the method comprising:

setting a first counter to zero prior to reading a data set;

reading the data set one or more times, the data set comprising a plurality of portions which combine together to wholly form the data set, wherein during each read of the data set, settings are changed in an attempt to better read the data set and the first counter is incremented by one;

storing all portions of the data set to a reserved data buffer after a first reading of the data set;

determining whether the stored data set is correctable using at least one of C1-error correction code (ECC) and C2-ECC, wherein when the data set is correctable using at least one of C1-ECC and C2-ECC, the stored data set is recovered;

determining whether the first counter equals a predetermined threshold prior to each read of the data set, wherein when the first counter equals the predetermined threshold the data set is reported as unreadable;

setting a second counter to zero prior to rereading the data set;

rereading portions assumed to be in the data set;

performing a validity check to determine whether a currently read portion is in the data set;

determining that the currently read portion of the data set is correctable using C1-ECC using a syndrome check when the validity check confirms that the portion is from the data set;

storing one or more of the portions of the data set to the reserved data buffer after subsequent readings of the data set when the one or more portions are correctable using C1-ECC;

determining that all portions of the data set have been reread according to the second counter, wherein the second counter is incremented by one after any of;

storing a portion of the data set, determining that the currently read portion is not in the data set, and determining that the currently read portion of the data set is not correctable using C1-ECC;

aggregating the one or more portions of the data set in the reserved data buffer to form an assembled data set, wherein each of the one or more portions are correctable using C1-ECC;

determining whether C2-ECC is capable of correcting all errors in the assembled data set;

correcting any remaining errors in the assembled data set using C2-ECC to form a reconstructed data set and sending the reconstructed data set to a host when C2-ECC is capable of correcting all errors in the assembled data set; and

rereading the data set using a different setting in an error recovery procedure (ERP) when an error in the assembled data set is not correctable using C2-ECC.

8. The method as recited in claim 7, wherein the plurality of portions of the data set are C1-encoded rows in an array representing the data set.

9. The method as recited in claim 7, wherein when a portion already exists in the reserved data buffer, the existing portion is overwritten when a corresponding portion from the one or more portions that are correctable using C1-ECC has fewer corrected errors therein than the existing portion.

10. The method as recited in claim 7, wherein the data set is reread, existing portions in the reserved data buffer are overwritten with portions having fewer errors corrected therein, and it is determined whether C2-ECC is capable of correcting all errors in the assembled data set until either the reconstructed data set is sent to the host, or a number of allowable retries is reached. and the data set is reported to the host as unreadable.

11. The method as recited in claim 7, wherein the data set is read from a magnetic tape.

12. The method as recited in claim 7, wherein different settings comprise a change to at least one of:

a tape speed during reading, a data flow correction power, channel parameters, and servo tracking.