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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
Old 06-23-2013
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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pvcreate(1M)															      pvcreate(1M)

NAME
pvcreate - create physical volume for use in LVM volume group SYNOPSIS
soft_defects] disk_size] disk_type] pv_path DESCRIPTION
The command initializes a direct access storage device (a raw disk device) for use as a physical volume in a volume group. If pv_path contains a file system and the option is not specified, asks for confirmation. The request for confirmation avoids accidentally deleting a file system. Furthermore, when the option is not specified, the operation is denied if pv_path already belongs to another LVM volume group, or the pv_path refers to a disk device under the control of the VERITAS or Oracle ASM Volume Manager. After using to create a physical volume, use to add it to a new volume group or to add it to an existing volume group (see vgcreate(1M) and vgextend(1M)). Disks cannot be added to a volume group until they are properly initialized by pv_path can be made into a bootable disk by specifying the option, which reserves space on the physical volume for boot-related data. This is a prerequisite for creating root volumes on logical volumes. Refer to mkboot(1M) and lif(4) for more information. Options and Arguments recognizes the following options and arguments: pv_path The character (raw) device path name of a physical volume. Read from standard input the numbers that correspond to the indexes of all known bad blocks on the physical volume, pv_path, that is being created. Specify the indexes using decimal, octal, or hexadecimal numbers in standard C-language nota- tion, with numbers separated by newline, tab, or formfeed characters. If this option is not used, assumes that the physical volume contains no bad blocks. This option is being retained solely for backward compatibility reasons and is currently ignored. It will be obsoleted in the next HP-UX release. Make a bootable physical volume (that is, a system disk). On PA-RISC systems, pv_path should be the path name for the whole disk. On Itanium(R)-based systems, pv_path should be the path name for the disk section containing the HP-UX partition (see model(1), getconf(1)). Booting from a volume group version 2.0 or higher is not supported. Therefore,a physical volume initialized with the option cannot be added to a volume group version 2.0 or higher. Specify the minimum number of bad blocks that LVM should reserve in order to perform software bad block relocation. This number can be no larger than 7039. If not specified, one block is reserved for each 8K of data blocks. This option is being retained solely for backward compatibility reasons and is currently ignored. It will be obsoleted in the next HP-UX release. Effective size of the physical volume to be created, specified in kilobytes (KB). This option is only supported on version 1.0 volume groups. When a physical volume is added to a volume group version 2.0 or higher any value set using the option is replaced with the full size of the disk (up to the maxi- mum physical volume size). Force the creation of a physical volume (thus deleting any file system or volume manager information present) without first requesting confirmation. Warning: The option should only be used as a last resort to over write file system or volume manager information that cannot properly be removed using the commands designed for that purpose. When invoked with the command does minimal verification, so care should be taken to assure that the disk is not already in use prior to invok- ing the command. Retrieve configuration information about the physical volume from the file disk_type specifies the device (for example, hp7959S). The disk_type only needs to be specified when fails to get the size from the underlying disk driver. If the driver successfully returns the size of the device, disk_type is ignored. Note The user data size of the same physical volume may differ, when initialized by command under different releases of HP-UX. EXTERNAL INFLUENCES
Environment Variables determines the language in which messages are displayed. If is not specified or is null, it defaults to "C" (see lang(5)). If any internationalization variable contains an invalid setting, all internationalization variables default to "C" (see environ(5)). EXAMPLES
Create a physical volume on raw device and force the creation without confirmation: Create a bootable physical volume for an Itanium-based system on raw device and force the creation without confirmation: WARNINGS
If you are using command on an Itanium-based system boot disk, ensure that the specified device special file correspond to the HP-UX parti- tion. For example, initializes only the first 2,147,483,647 Kilobytes (2TB - 1KB) of disk space when the disk size exceeds this value. Disk space beyond this point will not be used by LVM. FILES
Disk geometry and disk partition characteristics for all disk devices on the system SEE ALSO
getconf(1), model(1), idisk(1M), mkboot(1M), vgcreate(1M), vgextend(1M), lif(4), intro(7), lvm(7). pvcreate(1M)
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