SCSI Commands: 48BSPACE Page 212EOD is detected before the requested logical position, then the logical position is setto that position.If the Code field is 001b, then the logical position is moved the number of file marksindicated by the Count field. If BOM or EOD is detected before the requested logicalposition, then the logical position is set to that position.If the Code field is 011b, then the logical position is set to after the last valid block ontape. In this case the count field is ignored.Any other value of the Code field will cause Check Condition status to be returned.Spacing to sequential file marks is not supported. Set marks are not supported. TheSense Key is set to Illegal Request and the Additional Sense is set to Invalid field inCDB (2400).3.36.2 Space-by-Count FunctionsThe Count field indicates both direction and number of blocks or filemarks to spaceover from the current logical position. A positive value N in the Count field moves thetape forward over N blocks or filemarks. A negative value -N (2's complement) in theCount field moves the tape backward over N blocks or filemarks. Zero in the countfield causes no tape movement and is not considered an error.When there are no exception conditions during space functions, forward tape motionends on the EOM side of the last block or filemark and reverse motion ends on theBOM side of the last block or filemark.If a filemark is encountered while spacing over blocks, a Check Condition Status isreturned. The Sense FM bit is set and the Sense Valid bit is set, indicating ResidualLength is non-zero.The Residual Length equals the difference in the requested count and the actualnumber of blocks spaced over not including the filemark. The tape is positioned onthe logical EOM side of the filemark if movement was forward or on the logical BOMside of the filemark if movement was reverse.If EOD is encountered while spacing forward, Check Condition is returned with 08hSense Key. Extended Sense Valid bit is set, indicating Residual Length is nonzero.If BOM is encountered while spacing in reverse, Check Condition is returned with40h Sense Key. Extended sense Valid bit is set, indicating a nonzero ResidualLength.If EOM is encountered while spacing forward, Check Condition is returned with 40hor 43h Sense Key. Extended Sense Valid bit is set, indicating a nonzero ResidualLength.If an unrecoverable data error is encountered, Check Condition is returned,Extended Sense Key is set to Medium Error, and Extended Sense Valid bit is set,indicating Residual Length is nonzero.
