Seagate ST32000646SS Constellation ES SAS Product Manual - Page 54

The drive firmware error recovery algorithms consist of 12 levels for read recoveries and five levels for write. Each level may consist of multiple steps, where a step is defined as a recovery function involving a single reread or re-write attempt. The maximum level used by the drive in LBA recovery is determined by the read and write retry counts. Table 5 equates the read and write retry count with the maximum possible recovery time for read and write recovery of individual LBAs. The times given do not include time taken to perform reallocations. Reallocations are performed when the ARRE bit (for reads) or AWRE bit (for writes) is one, the RC bit is zero, and the recovery time limit for the command has not yet been met. Time needed to perform reallocation is not counted against the recovery time limit. When the RC bit is one, reallocations are disabled even if the ARRE or AWRE bits are one. The drive will still perform data recovery actions within the limits defined by the Read Retry Count, Write Retry Count, and Recovery Time Limit parameters. However, the drive does not report any unrecovered errors. Table 5: Read and write retry count maximum recovery times Maximum recovery time per Read retry count LBA (cumulative, ms) 0 108.29 1 124.95 2 424.83 3 458.15 4 483.14 5 590.16 6 644.92 7 711.56 8 898.54 9 1049.49 10 1116.13 11 1174.44 12 (default) 2311.47 Maximum recovery time per Write retry count LBA (cumulative, ms) 0 23.94 1 35.91 2 55.86 3 67.83 4 119.79 5 (default) 147.72 Setting these retry counts to a value below the default setting could result in degradation of the unrecovered error rate. For example, suppose the read/write recovery page has the RC bit = 0, the read retry count set to 4, and the recovery time limit set to 450. A 4-block read command can take up to 483.14ms recovery time for each block and a maximum of 450ms recovery for all four blocks. If either of these limits is reached and a block has not yet been recovered, the command will end with Check Condition status and an unrecoverable read error will be reported. 10.3 SAS system errors Information on the reporting of operational errors or faults across the interface is given in the SAS Interface Manual. The SSP Response returns information to the host about numerous kinds of errors or faults. The Receive Diagnostic Results reports the results of diagnostic operations performed by the drive. Status returned by the drive to the initiator is described in the SAS Interface Manual. Status reporting plays a role in systems error management and its use in that respect is described in sections where the various commands are discussed. 46 Constellation ES Series SAS Product Manual, Rev. F