The size of the Volume Manager private region partition always starts and ends on cylinder boundaries.  The reason for this is that Solaris partitions must start and end on cylinder boundaries.  

The vxdisksetup command can be used to specify non-default private and public region sizes.

Note:  In different versions of VxVM,  default private region size is not the same.

Syntax of vxdisksetup (for other options see vxdisksetup(1M) manpage) :
# /usr/lib/vxvm/bin/vxdisksetup -i cXtYdZ  privlen=  privoffset=  publen=  puboffset=

If the privlen attribute is specified and does not evenly divided into a number of sectors per cylinder,  then it is always rounded up to the next cylinder.


EXAMPLE

Volume Table Of Contents (VTOC) of a disk.  Disk below has 1506 sectors per cylinder:

# prtvtoc /dev/rdsk/c1t12d0s2
prtvtoc /dev/rdsk/c1t12d0s2
* /dev/rdsk/c1t12d0s2 partition map
*
* Dimensions:
*     512 bytes/sector
*     502 sectors/track
*       3 tracks/cylinder
*    1506 sectors/cylinder
*   11896 cylinders
*   11894 accessible cylinders
*
* Flags:
*   1:unmountable
*  10:read-only
*
*                          First    Sector    Last
*Partition  Tag  Flags    Sector    Count    Sector  Mount Directory
     2      5    01          0  17912364  17912363

Initialize this disk into VxVM with a custom private region size, 3013 sectors:

# /usr/lib/vxvm/bin/vxdisksetup -i c1t12d0 privlen=3013  

In this case 3013 sectors = 2 cylinders (1506 *2 = 1312) + 1 sector.  Because private region is a Solaris partition,  it must start and end on cylinder boundaries. As a result,  the size of the private region is rounded up to the next cylinder.  Below is the new disk VTOC:

# prtvtoc -h /dev/rdsk/c1t12d0s2
     2      5    01          0  17912364  17912363
     3    15    01          0      4518      4517
     4     14    01      4518  17907846  17912363

The resulting private partition size is not 3013 sectors,  but is 4518 sectors (3 cylinders).

Private region size can also be viewed with vxdisk list .

# vxdisk list c1t12d0 | grep private:
private:   slice=3 offset=1 len=4517