NAME

dd − SCSI disk driver

DESCRIPTION

The dd driver operates SCSI drives that support the Common Command Set. 

A drive can contain up to 7 partitions, commonly used to store multiple UNIX and AmigaDOS file systems.  The partitioning information, called the Rigid Disk Block, is stored on the disk.  Partition 0 is always present, and refers to the physical disk. 

A SCSI controller can operate up to 7 SCSI devices, with SCSI unit ID’s of 0 through 6.  SCSI unit ID 7 refers to the controller itself.  The A3000 internal controller and the A2091 controller card support SCSI bus disconnect/reselect, although the WD33C93A SCSI controller chip is required.  Older WD33C93 chips can be upgraded, if desired. 

Amiga UNIX can operate 2 controllers in its typical configuration.  SCSI controller cards are numbered according to their auto-config bus address.  On the A3000, the internal controller is number 0, followed by the card closest to the motherboard.  On the A2000, the card closest to the power supply is number 0. 

Disk drive storage is accessed through a device file whose minor device number identifies the controller card c, drive ddd and partition ppp. The low-order bits of the minor device number are interpreted as follows:

pppcddd

Cooked devices perform i/o through the kernel’s disk buffer cache.  Raw devices bypass the cache, but requests must observe certain restrictions: the data buffer must be longword-aligned, and the byte count must be a multiple of 512. 

FILES

/dev/dsk/c?d0s?cooked devices

/dev/rdsk/c?d0s?raw devices

SEE ALSO

rdb(1A), intro(7A)

DIAGNOSTICS

Error messages have the form:

controller: disk name: blkno key code

where controller is the type of controller (A3000, A2091, etc.), name is the device name as found in /dev/dsk, blkno is the physical block number, key is the general error category and code is additional error info.  A key of 6 (Unit Attention) is harmless, while 3 (Medium Error) usually indicates a damaged or deteriorating magnetic surface. 

NOTES

Driver behavior is undefined if the addressed SCSI device is not a disk. 

  —  Last change: 18-jul-91