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Full Discussion: Issue about PP size
Operating Systems AIX Issue about PP size Post 302757065 by MichaelFelt on Thursday 17th of January 2013 04:21:04 AM
Old 01-17-2013
The differences in PP - Physical Partition - sizes is caused by a number of defaults or constants re: the meta data for managing the volumes (aka disks) in a volume group.

The default size for a PP is actually 4M - dating back to when disks were smaller than 4G - because the default number of PP per volume has remained the same - 1016.

When disks were 4G and smaller the VGDA (Volume Group Descriptor Area) was 32M Byte large (or 8 x 4M, so a volume was 32M for VGDA (i.e. 8PP) with upto 1016 (1024 - 8) PP for volume group data.

The VGDA is an important structure - there are three kinds or sizes: normal, big and scaled. Normal is the original and it has space for 32 volumes of 1016 PP each, the big for 128 volumes of 1016 PP each, and the scaled originally began as 1024 disks of 1016 PP each, but now it is meant to scale/grow the max number of PP as the volume grows. But still the original factor of PP per disk is 1016.

Early on (with 4.5 and 9.1 G disks) AIX made changes to affect the number of PP per disk, e.g., so the PP size could be held constant even though disk sizes changed - however, the total number of PP per volume group (a VGDA constant) was fixed. The effect is that changing the number of PP per disk (the -t option of mkvg) means fewer disks can be included in a volume group (normal, and big are fixed at 32 and 128 by defaults).

So, basically, to keep a constant PP size over multiple disk sizes you need to divide the disk size by that PP size to see how many PP that will need, divide that number by 1016, round that number up to the next whole number (i.e., 2033 will need a factor of 3, or 3048 PP (-t 2 if I recall correctly) per volume while 2031 or 2032 will work with a factor of -t 1

Code:
-t 0 - default 1016
-t 1 - 2032 
-t 2 - 3048 
-t 3 - 4064
-t 4 - 5080
etc

Note: adding a disk larger than the original will mean it will not be fully utilized, however, you may change the scaling to a higher number dynamically (say you have been using 75G as a default, and want to add 150G disk/LUN. With no change, only 75G of the disk would be used. Change the scaling: the max number of disks declines, but the 150G disk can be fully utilized.

IMPOORTANT: you cannot change the PP size once a volume group is created. To change the PP size you must backup/restore to a new volume group.

Hope this helps!
 

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vxvmconvert(1M) 														   vxvmconvert(1M)

NAME
vxvmconvert - convert LVM volume groups to VxVM disk groups SYNOPSIS
vxvmconvert DESCRIPTION
vxvmconvert is a menu-driven program to convert an HP Logical Volume Manger (LVM) configuration to a Veritas Volume Manager configuration. This man page is a brief overview of vxvmconvert. Refer to the Veritas Volume Manager Migration Guide for a detailed description before using the conversion procedure. The vxvmconvert script is interactive and prompts you for responses, supplying defaults where appropriate. There is a Help facility at every prompt. Enter a question mark (?) at a prompt to display a context-sensitive help message. With vxvmconvert you can identify LVM volume groups, list disks, analyze volume groups for conversion and complete the conversion of LVM volume groups to VxVM disk groups. LVM configurations are converted at the volume group level. All disks used in a volume group are converted together. You cannot use vxvm- convert to convert unused LVM disks (those not part of an LVM volume group) to VxVM disks. To convert unused LVM disks, use pvremove to take the disk out of LVM control, then initialize the disk for VxVM use by using vxdiskadm (see pvremove(1M) and vxdiskadm(1M) for more information). vxvmconvert changes disks within LVM volume groups to VxVM disks by replacing the areas of the disks used for LVM configuration information and with the equivalent VxVM volume configuration information. Portions of the disks used for user data, such as file systems and data- bases, are not affected by the conversion. The conversion process changes the names by which your system refers to the logical storage, so must be done offline. No applications can access data in the volume groups undergoing conversion. You must unmount file systems using those volumes and shut down any applications, such as databases, that might use the volumes directly. OPERATIONS
Analyze LVM Volume Groups for Conversion Use this operation to analyze one or more LVM volume groups for conversion to use by VxVM. The analysis checks for problems that can prevent the conversion from completing successfully. It calculates the space required to add volume group disks to a Volume Manager disk group. More than one volume group may be entered at the prompt. A grep-like pattern may be used to select multiple volume groups. See the ``Limitations in Conversion'' section in the Volume Manager Migration Guide for more information. Convert LVM Volume Groups to VxVM Converts one or more LVM volume groups to one or more VxVM disk groups. This adds the disks to a VxVM disk group and replaces existing LVM volumes with VxVM volumes. vxvmconvert prompts you to name the VxVM disk group that replaces the LVM volume group being converted. A default is suggested at the prompt. For example, if you are converting a volume group vg08, vxvmconvert renames it as dg08. See to the sections ``Dealing with New Logical Volume Names'' and ``Tailoring your VxVM Configuration'' in the Volume Manager Migration Guide for more information. Rollback from VxVM to LVM Rollback reverts VxVM disk groups to LVM volume groups. vxvmconvert provides a limited snapshot capability for the LVM metadata in a converted volume group. A snapshot is a simple protection method to use during conversion. Caution! Do not use this operation if the VxVM disk group was modified since the conversion. See to the section ``Restoring LVM Volume Groups and Disaster Recovery'' in the Volume Manager Migration Guide for more informa- tion. List Disk Information Displays information about the disks on a system. You can obtain detailed information about a disk by entering a specific disk device address. List LVM Volume Group Information Listvg displays a list of LVM volume groups. You can obtain detailed information about an LVM volume group at a specific disk device address. SEE ALSO
pvremove(1M), vgcfgbackup(1M), vgrestore(1M), vxdisk(1M), vxdiskadd(1M), vxdiskadm(1M), vxintro(1M) Veritas Volume Manager Migration Guide VxVM 5.0.31.1 24 Mar 2008 vxvmconvert(1M)
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