Notes on OS/2 Disk Usage II - The Logical Volume Manager

By: Walter Metcalf

1 2 3 Next

In the previous article I noted that the size of hard drives has exploded in recent years. This has affected not only corporate users, especially those who use their computers to house information for the internet, but SOHO users as well. Whereas a few years ago, users were more than satisfied with 10 MB drives, now even many SOHO users feel they must have drives in excess of 60 GB. Use of multiple, sophisticated operating systems, use of increasingly complex and sophisticated applications such as Visual Age C++, easy access to multimedia files on the internet, and use of large databases have all contributed to this phenomenon.

All of these have conspired to render the traditional methods of accessing data such as FAT and even HPFS increasingly inadequate. Consequently IBM introduced a new method of accessing data for the OS/2 Warp Server for e-Business. This same method of access was introduced into the OS/2 Client as part of the first Merlin Convenience Pak (MCP). Since the MCP forms the foundation of eComStation, eCS also contains this new method of accessing hard drives.

What is this new method of accessing hard drives? It actually comprises two parts. One component is Logical Volume Manager (LVM), a replacement for and extension of the old FDISK. The second, and key component, is the Journaled File System (JFS).1 In this article, we shall deal with the LVM. We shall deal with the JFS in a later article in this series.2

LVM Management System

Unlike the old FDISK, which is a simple utility, the LVM is a whole layer of technology that provides many features completely unavailable using FDISK. Some of the more important of these are disk spanning, dynamic resizing, and sticky drive letters. Before we proceed further, let us look at some of the terminology used to describe the functioning of the LVM.

  1. Physical Partition

    A partition is a portion of the physical disk that functions as though it were a physical separate unit. Partitions are of two types: primary and extended. The first physical disk must always have at least one primary partition, and each drive can have at most one extended partition. Primary partitions cannot be subdivided any further, whereas extended partitions can be subdivided into smaller partitions (called logical drives or partitions).

  2. Logical Partition

    Subdivision within an extended partition, which is seen by the operating system as a separate unit.

  3. Logical Volume

    A logical volume can be either a single partition or a collection of partitions. In either case, they are presented to the application as a single unit with a single drive letter. They can be of two types:

    1. Compatibility (with previous versions of OS/2) or LVM.

      Compatibility volumes can be formed with either FAT or HPFS and can be made bootable.

    2. LVM

      LVM volumes can only be recognized by the Logical Volume Manager and can be formatted with JFS as well as FAT and HPFS. However, at this time, they cannot be made bootable.

  4. Overview of LVM

    Click the following icon for an overview of LVM:

1 2 3 Next


1 Of course, as we have noted in previous articles, the LVM and JFS are not really new: they are new to OS/2; specifically they have been ported from AIX, IBM's UNIX clone, where they were developed, and then adapted to the OS/2 environment. One major adaptation that was needed was the inclusion of drive letters--Unix-based systems do not use drive letters.

2 Much of the material in this article is based on the IBM Redbook, Inside OS/2 Warp Server for e-business, Chapter 4.

Unless otherwise noted, all content on this site is Copyright © 2004, VOICE