05-16-2002
When a process sends requests to a rdsk type special file, it is talking directly to the driver. A read or a write goes directly to or from device. Reads and writes must be aligned on DEV_BSIZE boundaries or the results are undefined.
When a process sends requests to a dsk type special file, it is talking to high level os routines. A read or write goes to or from the buffer cache. If needed, the os will read new data into the buffer cache. There are no alignment restrictions. You can read or write any collection of bytes anywhere on the device. The os will send aligned requests to the driver, but this is hidden from the process. I/O requests that arise from accesses to a dsk type special file enter the driver via its strategy entry point, not the read and write entry points. The driver may resequence the requests to optimize overall performance.
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cmdk(7D) Devices cmdk(7D)
NAME
cmdk - common disk driver
SYNOPSIS
cmdk@target, lun : [ partition | slice ]
DESCRIPTION
The cmdk device driver is a common interface to various disk devices. The driver supports magnetic fixed disks and magnetic removable
disks.
The block-files access the disk using the system's normal buffering mechanism and are read and written without regard to physical disk
records. There is also a "raw" interface that provides for direct transmission between the disk and the user's read or write buffer. A sin-
gle read or write call usually results in one I/O operation; raw I/O is therefore considerably more efficient when many bytes are transmit-
ted. The names of the block files are found in /dev/dsk; the names of the raw files are found in /dev/rdsk.
I/O requests to the magnetic disk must have an offset and transfer length that is a multiple of 512 bytes or the driver returns an EINVAL
error.
Slice 0 is normally used for the root file system on a disk, slice 1 as a paging area (for example, swap), and slice 2 for backing up the
entire fdisk partition for Solaris software. Other slices may be used for usr file systems or system reserved area.
Fdisk partition 0 is to access the entire disk and is generally used by the fdisk(1M) program.
FILES
/dev/dsk/cndn[s|p]n block device (IDE)
/dev/rdsk/cndn[s|p]n raw device (IDE)
where:
cn controller n
dn lun n (0-7)
sn UNIX system slice n (0-15)
pn fdisk partition(0)
/kernel/drv/cmdk 32-bit kernel module.
/kernel/drv/amd64/cmdk 64-bit kernel module.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Architecture |x86 |
+-----------------------------+-----------------------------+
SEE ALSO
fdisk(1M), mount(1M), lseek(2), read(2), write(2), readdir(3C), scsi(4), vfstab(4), attributes(5), dkio(7I)
SunOS 5.10 9 Oct 2004 cmdk(7D)