RA(4) RA(4)
NAME
ra - DEC MSCP disks (RA60, RA80, RA81, RA90)
DESCRIPTION
Ra devices occupy disk drives conforming to DEC's Mass Stor-
age Control Protocol standard: drives such as the RA81 con-
nected via controllers such as the UDA50. Files with minor
device numbers 0 through 7 refer to different sections of
drive 0, minor devices 8 through 16 refer to drive 1, and so
on up to 63 (8 drives).
Normally the disk is accessed in 1024-byte blocks (1K). If
64 is added to the minor device number, 4096-byte blocks
(4K) are used instead. A 4K device mounted as a file system
is bitmapped; see filsys(5).
Conventionally the files are given names like `ra37' for
section 7 of drive 3. There are no name rules distinguish-
ing 1024-byte files from 4096-byte files; in practice the
files are almost always the 4096-byte kind.
The start and size of the sections of each drive are as fol-
lows. Sizes are measured in 512-byte hardware sectors.
disk start length
0 0 10240
1 10240 20480
2 30720 249848
3 280568 249848
4 530416 249848
5 780264 arbitrarily large
6 30720 749544
7 0 arbitrarily large
The `arbitrarily large' sections reach to the end of the
disk. Rarct will display disk sizes; see rarepl(8). For
example, an RA81 has 891072 sectors, so section 7 is that
size, and section 5 is 891072-780264=110808 sectors. An
RA90 has 2376153 sectors; section 7 is that size, section 5
is 2376153-780264=1595889 sectors. For other disks, run
rarct and do the arithmetic.
The ra files discussed above access the disk via the
system's normal buffering mechanism and may be read and
written without regard to physical disk records. There is
also a `raw' interface which provides for direct transmis-
sion between the disk and the user's read or write buffer.
A single read or write call results in exactly one I/O oper-
ation and therefore raw I/O is considerably more efficient
when many words are transmitted. The names of the raw files
RA(4) RA(4)
begin with `rra' and end with a number which selects the
same disk as the corresponding `ra' file.
In raw I/O the buffer must begin on a word boundary, and
counts should be a multiple of 512 bytes (a disk block).
Likewise lseek(2) calls should specify a multiple of 512
bytes.
Several ioctl(2) calls apply to the raw devices.
UIOCHAR The third argument to ioctl points to an object to
be filled with drive parameters:
struct ud_unit {
daddr_t radsize; /* disk size, sectors */
daddr_t rctsize; /* RCT size, including pad */
long medium; /* medium id */
short tracksz; /* sectors per track */
short groupsz; /* tracks per group */
short cylsz; /* groups per cylinder */
char rbns; /* RBNs per track */
char copies; /* number of RCT copies */
};
UIORRCT The third argument points to an object of type
struct ud_rctbuf {
caddr_t buf;
int lbn;
};
buf points to a 512-byte buffer, into which block
lbn of the replacement and caching table (RCT) is
read. As many copies of the RCT as necessary are
examined to find a readable copy of the block.
UIOWRCT The third argument is like that of UIORRCT. Block
lbn of the RCT is written in all copies.
UIOREPL The third argument points to an object of type:
struct ud_repl {
daddr_t replbn; /* good block */
daddr_t lbn; /* bad block */
short prim; /* nonzero if primary replacement */
};
A `replace' command is sent to the controller,
requesting that attempts to access logical block
lbn henceforth be revectored to replacement block
replbn. Prim should be set nonzero if and only if
replbn is the primary replacement block for lbn.
UIOSPDW Arrange that the disk drive will spin down when the
last file using it is closed.
UIORST Reset the controller to which this disk is con-
nected. Any pending operations are abandoned and
return an error.
FILES
SEE ALSO
RA(4) RA(4)
rarepl(8)
MSCP Basic Disk Functions Manual
DEC Standard Disk Format Specification
BUGS
In raw I/O read(2) and write truncate file offsets to 512-
byte block boundaries, and write scribbles on the tail of
incomplete blocks. Thus, in programs that are likely to
access raw devices, read, write and lseek(2) should always
deal in 512-byte multiples.
UIORRCT and UIOWRCT will misbehave if invoked on a section
that doesn't start at the beginning of the disk. Section 7
(the whole disk) is the best choice.
The 1K/4K flag bit in the device number is unfortunate.