03-23-2006
character driver (rdsk)
The driver has read and write entry points. The read and write system calls pass this off to the driver. The driver decides if the operation succeeds or not. If it fails, the driver can set any errno value it wants. There are standards, but some driver writers do not follow them. There are rules to follow and they can vary from driver to driver. Typically you must start a read or write on a disk sector boundary. And you must write full sectors. If you try to write a partial sector, and the driver allows it, you will probably garble the rest of the sector. Data moves directly to/from the disk to/from your program. There is no synchronization with data in the buffer cache.
block driver (dsk)
The driver has no read or write entry points. You cannot talk to the driver in a direct manner. The kernel must prepare a buffer header to pass to the driver's strategy entry point. read() and write() should strongly follow the man page. No sector boundary rules. You can write a single byte and it should work. Data must flow to/from the buffer cache and then to/from your program; and thus is in sync with any recent changes.
(Note that the "in sync" implies operations to the same device. If you mount a slice of a disk, then dd the whole disk via another special file, it won't be in sync.)
I would always use rdsk to avoid copying the data around in core. Your 9 hours vs 15 minutes is very extreme. You don't give any particulars of your situation. But it does not take 8 hours and 45 minutes to do the in-core copying of data that can be read in 15 minutes. I don't enough info to guess what happened.
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volfs(7FS) File Systems volfs(7FS)
NAME
volfs - Volume Management file system
DESCRIPTION
volfs is the Volume Management file system rooted at root_dir. The default location for root-dir is /vol, but this can be overridden using
the -d option of vold (see vold(1M)). This file system is maintained by the Volume Management daemon, vold, and will be considered to be
/vol for this description.
Media can be accessed in a logical manner (no association with a particular piece of hardware), or a physical manner (associated with a
particular piece of hardware).
Logical names for media are referred to through /vol/dsk and /vol/rdsk. /vol/dsk provides block access to random access devices. /vol/rdsk
provides character access to random access devices.
The /vol/rdsk and /vol/dsk directories are mirrors of one another. Any change to one is reflected in the other immediately. The dev_t for a
volume will be the same for both the block and character device.
The default permissions for /vol are mode=0555, owner=root, group=sys. The default permissions for /vol/dsk and /vol/rdsk are mode=01777,
owner=root, group=sys.
Physical references to media are obtained through /vol/dev. This hierarchy reflects the structure of the /dev name space. The default per-
missions for all directories in the /vol/dev hierarchy are mode=0555, owner=root, group=sys.
mkdir(2), rmdir(2), unlink(2) (rm), symlink(2) (ln -s), link(2) (ln), and rename(2) (mv) are supported, subject to normal file and direc-
tory permissions.
The following system calls are not supported in the /vol filesystem: creat(2), only when creating a file, and mknod(2).
If the media does not contain file systems that can be automatically mounted by rmmount(1M), users can gain access to the media through the
following /vol locations:
+-----------------------------------+------------------------------------+
| Location | State of Media |
+-----------------------------------+------------------------------------+
|/vol/dev/diskette0/unnamed_floppy | formatted unnamed floppy-block |
| | device access |
+-----------------------------------+------------------------------------+
|/vol/dev/rdiskette0/unnamed_floppy | formatted unnamed floppy-raw |
| | device access |
+-----------------------------------+------------------------------------+
|/vol/dev/diskette0/unlabeled | unlabeled floppy-block device |
| | access |
+-----------------------------------+------------------------------------+
|/vol/dev/rdiskette0/unlabeled | unlabeled floppy-raw device access |
+-----------------------------------+------------------------------------+
|/vol/dev/dsk/c0t6/unnamed_cdrom | CD-ROM-block device access |
+-----------------------------------+------------------------------------+
|/vol/dev/rdsk/c0t6/unnamed_cdrom | CD-ROM-raw device access |
+-----------------------------------+------------------------------------+
For more information on the location of CD-ROM and floppy media, see System Administration Guide: Basic Administration or rmmount(1M).
Partitions
Some media support the concept of a partition. If the label identifies partitions on the media, the name of the media becomes a directory
with partitions under it. Only valid partitions are represented. Partitions cannot be moved out of a directory.
For example, if disk volume 'foo' has three valid partitions, 0, 2, and 5, then:
/vol/dsk/foo/s0
/vol/dsk/foo/s2
/vol/dsk/foo/s5
for block access and
/vol/rdsk/foo/s0
/vol/rdsk/foo/s2
/vol/rdsk/foo/s5
for character access.
If a volume is relabeled to reflect different partitions, the name space changes to reflect the new partition layout.
A format program can check to see if there are others with the volume open and not allow the format to occur if it is. Volume Management,
however, does not explicitly prevent the rewriting of a label while others have the volume open. If a partition of a volume is open, and
the volume is relabeled to remove that partition, it will appear exactly as if the volume were missing. A notify event will be generated
and the user may cancel the operation with volcancel(1), if desired.
SEE ALSO
volcancel(1), volcheck(1), volmissing(1) rmmount(1M), vold(1M), rmmount.conf(4), vold.conf(4)
System Administration Guide: Basic Administration
SunOS 5.10 8 Feb 1995 volfs(7FS)