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Operating Systems AIX Difference between /dev/hdisk and /dev/rhdisk Post 302825147 by MichaelFelt on Sunday 23rd of June 2013 06:38:50 PM
Old 06-23-2013
Basically, for all *NIX systems, filesystems are created and used via block devices, not character devices.

By definition, character devices have a window of 1 char - a driver might buffer that a little bit (so you can unchar(), or back up one byte.

Block devices are, by definition - finite in size (while char devices may be infinite) - and block devices are "seekable". Because they are seekable, an information system, such as a file system can be stored on them.

Note: some device drivers use ioctl() to perform actions similar to seek - hence the confusion. However, the original definition (at least as far back as UNIX v6) was that character devices did not seek.
 

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devfs(7FS)                                                         File Systems                                                         devfs(7FS)

NAME
devfs - Devices file system DESCRIPTION
The devfs filesystem manages a name space of all devices under the Solaris operating environment and is mounted during boot on the /devices name space. The /devices name space is dynamic and reflects the current state of accessible devices under the Solaris operating environment. The names of all attached device instances are present under /devices. The content under /devices is under the exclusive control of the devfs filesystem and cannot be changed. The system may be configured to include a device in one of two ways: By means of dynamic reconfiguration (DR), using, for example, cfgadm(1M). For devices driven by driver.conf(4) enumeration, edit the driver.conf file to add a new entry, then use update_drv(1M) to cause the system to re-read the driver.conf file and thereby enumerate the instance. The device may be attached through a number of system calls and programs, including open(2), stat(2) and ls(1). During device attach, the device driver typically creates minor nodes corresponding to the device via ddi_create_minor_node(9F). If the attach is successful, one or more minor nodes referring to the device are created under /devices. Operations like mknod(2), mkdir(2) and creat(2) are not supported in /devices. FILES
/devices Mount point for devfs file system SEE ALSO
devfsadm(1M), vfstab(4), attach(9E) NOTES
The /devices name space cannot be unmounted. All content at or below the /devices name space is an implementation artifact and subject to incompatible change or removal without notifi- cation. SunOS 5.10 26 Oct 2004 devfs(7FS)
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