term% cat index.txt RA(4) Kernel Interfaces Manual RA(4)
NAME
ra - DEC MSCP disks (RA60, RA80, RA81)
DESCRIPTION
Ra∗ refer to disk drives conforming to DEC's Mass Storage Control Pro‐
tocol standard: drives such as the RA81 connected via controllers such
as the UDA50. Files with minor device numbers 0 through 7 refer to
various portions of drive 0, minor devices 8 through 16 refer to drive
1, and so on up to 63. These files have a blocksize of 1K bytes; if 64
is added to the minor device number, the resulting file has 4K byte
blocks, and if used as a filesystem, a slightly different structure.
The range and size of the pseudo-drives for each drive are as follows.
Sizes are measured in hardware sectors (512 bytes).
disk start length
0 0 10240
1 10240 20480
2 30720 249848
3 280568 249848
4 530416 249848
5 780264 110808
6 30720 749544
7 0 arbitrarily large
Partition 7 covers the entire disk: 891072 sectors on an RA81.
The ra files discussed above access the disk via the system's normal
buffering mechanism and may be read and written without regard to phys‐
ical disk records. There is also a `raw' interface which provides for
direct transmission between the disk and the user's read or write buf‐
fer. A single read or write call results in exactly one I/O operation
and therefore raw I/O is considerably more efficient when many words
are transmitted. The names of the raw RA files 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. They are probably
useful only for bad block handling.
UIOCHAR The third argument to ioctl is a pointer to a struct ud_unit:
struct ud_unit {
daddr_t radsize;/* size of the disk */
daddr_t rctsize;/* size of the RCT, including pad */
long medium;
short tracksz;
short groupsz;
short cylsz;
char rbns;
char copies;
};
which the system fills with geometry parameters for the
drive.
UIORRCT The third argument points to a struct ud_rctbuf:
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 points to a struct ud_rctbuf; block lbn of
the RCT is written in all copies.
UIOREPL The third argument points to a struct ud_repl :
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.
FILES
/dev/ra*, /dev/rra*
SEE ALSO
rarepl(8)
MSCP Basic Disk Functions Manual
DEC Standard Disk Format Specification
BUGS
In raw I/O read and write(2) 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 partition that
doesn't start at the beginning of the disk. Partition 7 (the whole
disk) is the best choice.
This driver should be split into a generic disk driver and a port
driver, which communicate by exchanging MSCP packets.
RA(4)