Difference between /dev/hdisk and /dev/rhdisk Post: 302825089

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Operating Systems AIX Difference between /dev/hdisk and /dev/rhdisk Post 302825089 by bakunin on Sunday 23rd of June 2013 11:35:46 AM

06-23-2013

Registered User

It usually helps if you ask what you really want to know, instead of something vaguely related to that. We are not adverse to explaining things, but commonly get angry when we get the feeling that we are abused to cover a lack of energy.

Quote:

Originally Posted by jibujacob

I had gone through google prior to posting and couldnot identify whether my filesytem is made of the rawdisks or non-raw disks....

Your filesystem is made of volumes, neither raw nor other disks. That is the point of having a logical volume manager.

There is a driver for each certain (type of) disk: SCSI drives, LUNs, whatever. This driver creates a blockdevice and a character device. If you want to use the device directly, you can do that and, for instance, use a program like "dd" to write to it.

Otherwise you give this device to the LVM, which uses it to create Physical Volumes, PVs. "creating PVs" means it writes all sort of management-information onto it, like the VGDA (volume group descriptor area), etc.. Think of this like taking open (raw) land and build roads, create lots, and so on: the land is still unused, but now the means to use it are there.

Now you create Logical Volumes, LVs, on this now usable space. You can use such an LV like a raw device too (and this is sometimes done, for instance with databases), but it is not the same as the raw devices from before, because now this raw space is under control of the LVM and can be handled by its methods: it can be moved to another PV, increased in size, ...

Finally, you can create a filesystem on such an LV, instead of using the provided space directly. You could also create a swap space, a dump device or something entirely different instead. Depending on what you create a certain driver (for filesystems the filesystem driver) will use the LV to create the entity it is designed to provide.

I hope this clears it up a bit.

bakunin

Last edited by bakunin; 06-23-2013 at 12:43 PM..

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LEARN ABOUT MOJAVE

mkdevmaps

mkdevmaps(1M)                                             System Administration Commands                                             mkdevmaps(1M)

NAME

       mkdevmaps - make device_maps entries

SYNOPSIS

       /usr/sbin/mkdevmaps

DESCRIPTION

       The  mkdevmaps  command  writes  to standard out a set of device_maps(4) entries describing the system's frame buffer, audio, and removable
       media devices.

       The mkdevmaps command is used by the init.d(4) scripts to create or update the /etc/security/device_maps file.

       Entries are generated based on the device special files found in /dev. For the different  categories  of  devices,  the  mkdevmaps  command
       checks for the following files under /dev:

       audio           /dev/audio, /dev/audioctl, /dev/sound/...
       tape            /dev/rst*, /dev/nrst*, /dev/rmt/...
       floppy          /dev/diskette, /dev/fd*, /dev/rdiskette, /dev/rfd*
       removable disk  /dev/dsk/c0t?d0s?, /dev/rdsk/c0t?d0s?
       frame buffer    /dev/fb

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+
       |Interface Stability          |Obsolete                     |
       +-----------------------------+-----------------------------+

SEE ALSO

       allocate(1), bsmconv(1M), attributes(5)

NOTES

       mkdevmaps might not be supported in a future release of the Solaris operating system.

SunOS 5.10                                                          8 Oct 2003                                                       mkdevmaps(1M)