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1.1     ! root        1: .TH RA 4
        !             2: .CT 2 sa
        !             3: .SH NAME
        !             4: ra \- DEC MSCP disks (RA60, RA80, RA81, RA90)
        !             5: .SH DESCRIPTION
        !             6: .I Ra
        !             7: devices occupy disk drives conforming to
        !             8: DEC's Mass Storage Control Protocol standard:
        !             9: drives such as the RA81
        !            10: connected via controllers such as the UDA50.
        !            11: Files with minor device numbers 0 through 7
        !            12: refer to different sections of drive 0,
        !            13: minor devices 8 through 16 refer to drive 1,
        !            14: and so on up to 63 (8 drives).
        !            15: .PP
        !            16: Normally the disk is accessed in 1024-byte blocks (1K).
        !            17: If 64 is added to the minor device number,
        !            18: 4096-byte blocks (4K) are used instead.
        !            19: A 4K device mounted as a file system is bitmapped; see
        !            20: .IR filsys (5).
        !            21: .PP
        !            22: Conventionally the files are given names like
        !            23: .L ra37
        !            24: for section 7 of drive 3.
        !            25: There are no name rules distinguishing 1024-byte files
        !            26: from 4096-byte files;
        !            27: in practice the files are almost always the 4096-byte kind.
        !            28: .PP
        !            29: The start and size
        !            30: of the sections of each drive
        !            31: are as follows.
        !            32: Sizes are measured in
        !            33: 512-byte hardware sectors.
        !            34: .PP
        !            35: .nf
        !            36: .ta .5i +\w'000000    'u +\w'000000    'u
        !            37:        disk    start   length
        !            38:        0       0       10240
        !            39:        1       10240   20480
        !            40:        2       30720   249848
        !            41:        3       280568  249848
        !            42:        4       530416  249848
        !            43:        5       780264  arbitrarily large
        !            44:        6       30720   749544
        !            45:        7       0       arbitrarily large
        !            46: .DT
        !            47: .fi
        !            48: .PP
        !            49: The `arbitrarily large'
        !            50: sections reach to the end of the disk.
        !            51: .I Rarct
        !            52: will display disk sizes; see
        !            53: .IR rarepl (8).
        !            54: For example,
        !            55: an RA81 has 891072 sectors,
        !            56: so section 7 is that size,
        !            57: and section 5 is
        !            58: 891072\(mi780264=110808 sectors.
        !            59: An RA90 has 2376153 sectors;
        !            60: section 7 is that size,
        !            61: section 5 is
        !            62: 2376153\(mi780264=1595889 sectors.
        !            63: For other disks,
        !            64: run
        !            65: .I rarct
        !            66: and do the arithmetic.
        !            67: .PP
        !            68: The
        !            69: .I ra
        !            70: files
        !            71: discussed above access the disk via the system's normal
        !            72: buffering mechanism
        !            73: and may be read and written without regard to
        !            74: physical disk records.
        !            75: There is also a `raw' interface
        !            76: which provides for direct transmission between the disk
        !            77: and the user's read or write buffer.
        !            78: A single read or write call results in exactly one I/O operation
        !            79: and therefore raw I/O is considerably more efficient when
        !            80: many words are transmitted.
        !            81: The names of the raw files
        !            82: begin with
        !            83: .L rra
        !            84: and end with a number which selects the same disk
        !            85: as the corresponding
        !            86: .L ra
        !            87: file.
        !            88: .PP
        !            89: In raw I/O the buffer must begin on a word boundary,
        !            90: and counts should be a multiple of 512 bytes
        !            91: (a disk block).
        !            92: Likewise
        !            93: .IR lseek (2)
        !            94: calls should specify a multiple of 512 bytes.
        !            95: .PP
        !            96: Several
        !            97: .IR ioctl (2)
        !            98: calls
        !            99: apply to the raw devices.
        !           100: .TF UIORRCT
        !           101: .TP
        !           102: .B UIOCHAR
        !           103: The third argument to
        !           104: .I ioctl
        !           105: points to an object 
        !           106: to be filled with drive parameters:
        !           107: .EX
        !           108: .ta .5i +\w'daddr_t 'u +\w'radsize   'u
        !           109: struct ud_unit {
        !           110:        daddr_t radsize;        /* disk size, sectors */
        !           111:        daddr_t rctsize;        /* RCT size, including pad */
        !           112:        long    medium; /* medium id */
        !           113:        short   tracksz;        /* sectors per track */
        !           114:        short   groupsz;        /* tracks per group */
        !           115:        short   cylsz;  /* groups per cylinder */
        !           116:        char    rbns;   /* RBNs per track */
        !           117:        char    copies; /* number of RCT copies */
        !           118: };
        !           119: .EE
        !           120: .TF UIORRCT
        !           121: .TP
        !           122: .B UIORRCT
        !           123: The third argument points to an object of type
        !           124: .EX
        !           125: struct ud_rctbuf {
        !           126:        caddr_t buf;
        !           127:        int     lbn;
        !           128: };
        !           129: .EE
        !           130: .IP
        !           131: .B buf
        !           132: points to a 512-byte buffer,
        !           133: into which block
        !           134: .B lbn
        !           135: of the replacement and caching table
        !           136: (RCT)
        !           137: is read.
        !           138: As many copies of the RCT
        !           139: as necessary
        !           140: are examined to find a readable copy
        !           141: of the block.
        !           142: .TP
        !           143: .B UIOWRCT
        !           144: The third argument is like that of
        !           145: .BR UIORRCT .
        !           146: Block
        !           147: .B lbn
        !           148: of the RCT is written
        !           149: in all copies.
        !           150: .TP
        !           151: .B UIOREPL
        !           152: The third argument points to an object of type:
        !           153: .EX
        !           154: struct ud_repl {
        !           155:        daddr_t replbn; /* good block */
        !           156:        daddr_t lbn;    /* bad block */
        !           157:        short   prim;   /* nonzero if primary replacement */
        !           158: };
        !           159: .EE
        !           160: .IP
        !           161: A `replace' command
        !           162: is sent to the controller,
        !           163: requesting that attempts to access logical block
        !           164: .I lbn
        !           165: henceforth be revectored to replacement block
        !           166: .IR replbn .
        !           167: .I Prim
        !           168: should be set nonzero
        !           169: if and only if
        !           170: .I replbn
        !           171: is the primary replacement block for
        !           172: .IR lbn .
        !           173: .TP
        !           174: .B UIOSPDW
        !           175: Arrange that the disk drive will spin down
        !           176: when the last file using it is closed.
        !           177: .TP
        !           178: .B UIORST
        !           179: Reset the controller
        !           180: to which this disk is connected.
        !           181: Any pending operations are abandoned and return an error.
        !           182: .SH FILES
        !           183: .F /dev/ra*
        !           184: .br
        !           185: .F /dev/rra*
        !           186: .SH SEE ALSO
        !           187: .IR rarepl (8)
        !           188: .br
        !           189: MSCP Basic Disk Functions Manual
        !           190: .br
        !           191: DEC Standard Disk Format Specification
        !           192: .SH BUGS
        !           193: In raw I/O
        !           194: .IR read (2)
        !           195: and
        !           196: .IR write 
        !           197: truncate file offsets to 512-byte block boundaries,
        !           198: and
        !           199: .I write
        !           200: scribbles on the tail of incomplete blocks.
        !           201: Thus,
        !           202: in programs that are likely to access raw devices,
        !           203: .I read, write
        !           204: and
        !           205: .IR lseek (2)
        !           206: should always deal in 512-byte multiples.
        !           207: .PP
        !           208: .B UIORRCT
        !           209: and
        !           210: .B UIOWRCT
        !           211: will misbehave if invoked on a section
        !           212: that doesn't start
        !           213: at the beginning of the disk.
        !           214: Section 7
        !           215: (the whole disk)
        !           216: is the best choice.
        !           217: .PP
        !           218: The 1K/4K flag bit in the device number is unfortunate.

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