HP OpenVMS Systems

Looking for disk partitioning tool?

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The Question is:

 
Where may I find a tool that can make some kind of disk partition on SCSI
disks?
 
 

The Answer is :

 
  Strictly speaking, you cannot create "partitions" on OpenVMS disk volumes
  (using the term "partition" in the DOS or Windows FAT sense) without the
  assistance of the storage hardware.  (A DOS partition is a set of data
  structures that permit multiple file system instances to coexist on the
  same disk.)
 
  Storage controllers (eg: the HSZ70, HSZ80, HSG80, HSJ50) allow you
  to divide physical disk volumes into partitions, which then appear as
  independent disk volumes to the host OpenVMS system.  This is,
  potentially, an expensive solution to your problem.
 
  There are tools available that can create "logical" or "virtual" disk
  volumes on a physical disk volume, akin to the IBM DASD model or the
  DOS partition model.  On OpenVMS, these "logical" volumes are implemented
  as a device driver, and particularly as a device driver which presents a
  disk-like device interface to the operating system, but that manages a
  container file on the physical disk, or that manages one or more ranges
  of disk logical blocks.  Two such tools are LDDRIVER and VDDRIVER (and
  variants), both of which are available on the OpenVMS Freeware CD-ROM
  distribution.  These tools can operate on any disk device (other than
  a system disk), and not just on a SCSI disk.  Among available commercial
  products that provide this is the RAID Software for OpenVMS package --
  you can create a RAID 0 or 0+1 set out of a single disk drive, and can
  then partition the virtual RAID device as required.
 
  Unlike the DOS partition approach, the low-level OpenVMS bootstrap device
  drivers are not capable of bootstrapping off a software-partitioned disk.
  Data disks can be partitioned.  Though a bootstrap is not possible from
  it, disk container files can certainly exist on the system disk as well
  as on data disks.  The OpenVMS bootstrap drivers are potentially (often)
  capable of bootstrapping off a controller-based partition.
 
  There are advantages and disadvantage to container files and to software
  partitioning in general.  The biggest disadvantage is that they are somewhat
  slower than accessing the disk directly; there is more driver software
  overhead involved.  The biggest advantage is that the container file is,
  really, just another file, and it can be moved around, backed up, etc.,
  without having to copy the data in the container file.
 
  Container files, logical-block-based drivers, and controller-based disk
  partitions -- because these all present the appearance of a smaller total
  disk capacity -- can also be used to permit smaller disk cluster factors.
  (The disk cluster factor is the minimal unit of storage allocation on a
  disk.)  This can potentially increase the available amount of useful
  storage, particularly when many smaller files exist on a large disk.
  (The average "wasted" space on a disk can be calculated based on half
  of the disk cluster factor times the number of files on the disk, on
  the assumption that half of the last disk cluster allocated to each
  file is unused.)
 
  OpenVMS V7.2 and later permit smaller disk cluster factors and these
  smaller cluster factors can make better use of storage when larger numbers
  of files are resident on larger disks.  Prior to V7.2, the minimum disk
  cluster factor scales with the size of the volume due to the size of the
  storage bitmap, and cluster factors of 18 and 36 blocks are not unusual.
  With V7.2 and later, a disk cluster factor of 1 is permitted on a volume
  of up to 137 GB in capacity, at which capacity the permitted minimum disk
  cluster factor doubles to 2.
 

  

     

     
answer written or last revised on ( 19-JAN-2000 )
     
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