Dell OpenManage Array Manager 2.5 User's Guide
The Array Manager Storage Model
This chapter describes the Array Manager storage model and its components. It also provides information about what RAID is and how different levels of RAID work.
The Array Manager storage model represents the different components in a storage subsystem as either physical or logical storage objects. The storage objects are in a hierarchical order. A computer object representing a local or remote computer running Array Manager is at the top of the hierarchy. You can have multiple computers at this level. Each computer displays a default tree view, which you can change. By default, the tree view displays three main objects below each computer:
In the sample screen above, the computer object at the top of the hierarchy, DELL4, represents the local computer running Array Manager. It has three storage objects beneath it, Arrays, Disks, and Volumes. The plus sign in front of each object indicates that additional subordinate objects exist under that object.
All the storage objects have context menus associated with them. To access a storage object's context menu, right-click on the object.
You can change the storage objects that you view in Array Manager by using the Add Categories function. See Change the Array Manager Category Display in The Array Manager Console chapter for more details.
Arrays represent the physical and logical storage subsystems connected to RAID controllers. The array consists of one or more subsystem objects. An example of a subsystem can be a PERC subsystem, which is a RAID controller-specific storage subsystem. A subsystem object consists of two subordinate storage objects:
In the sample screen above, the fully expanded Arrays object hierarchy shows both the Physical Array and the Logical Array. The Physical Array object has a PERC 2/SC controller that contains a single channel, Channel 0, with five array disks. The array disk numbering corresponds with the number of the channel and the SCSI ID. In the screen above, the array disks 0:0, 0:1, 0:2, 0:3, and 0:4 are connected to Channel 0 and occupy SCSI IDs 0 to 4.
The Logical Array object contains array groups. An array group has array disks that are controlled by a particular array controller. You can create multiple virtual disks from disks in an array group, depending on what the array controller supports. For example, array disks attached to Controller 0 will attach as Array Group 0.
A virtual disk is an abstract entity made up of array disks and/or array disk segments presented to an operating system as a single contiguous block of storage space. When you create a virtual disk, you are asked to specify a hardware RAID level.
An array disk is a disk controlled by the array controller. This disk can be placed in an array group, and virtual disks can be created from it.
As shown in the sample screen above, virtual disks created in a particular array group are listed under that Array Group object. These virtual disks also appear as Microsoft Windows NT or Windows 2000® disks under the Disks object. Virtual disks are placed under the Disks object because once a virtual disk is created, it is viewed by the operating system as a regular hard disk.
Disks represent the disks recognized by the Microsoft Windows NT or Windows 2000 operating system. This can include regular hard disks and virtual disks created through Array Manager. This view also includes removable media, such as CD-ROM drives or removable disks, such as Zip disks. The screen below shows an example of a Disks section of the tree view.
Disks are further classified as basic or dynamic.
A basic disk adheres to the partition-oriented scheme of Windows NT, Windows 95/98, and MS-DOS®. Basic disks can also contain RAID volumes that were created in NT Disk Administrator, including spanned volumes (volume sets), mirrored volumes (mirror sets), striped volumes (stripe sets), and RAID-5 volumes (stripe sets with parity). In addition, virtual disks, CD-ROMs, and removable-media disks are considered basic disks.
Dynamic disks are created by upgrading basic disks using Array Manager. A dynamic disk is a physical disk that can contain dynamic volumes created by Array Manager.
For more information about disks, see the Disk Management chapter.
A volume is a logical entity that is made up of portions of one or more physical disks. A volume can be formatted with a file system and can be accessed by a drive letter. The maximum size of a volume depends on the quantity of free disk space and the type of volume selected. The screen that follows shows an example of a Volumes section of the tree view.
Volumes can be:
In Array Manager, primary and extended partitions and logical drives exist only on basic disks. Basic disks use the traditional disk partitioning mechanism used by MS-DOS, Microsoft® Windows 95® or 98®, and Microsoft Windows NT®. A basic disk can have up to either four primary partitions or three primary partitions plus an extended partition. This extended partition can be subdivided into as many as 32 logical drives.
A logical drive is a simple volume that resides on an extended partition of a basic disk. You can use all or part of the free space in an extended partition when creating logical drives.
Basic volumes refer to all the volumes that are on basic disks. Basic volumes can be primary or extended partitions, simple logical drives that reside on extended partitions, or RAID volumes that were originally created in Windows NT Disk Administrator.
A dynamic volume is a logical volume that can be created only from a dynamic disk using Array Manager software. Dynamic volume types include simple, spanned, striped, mirrored, and RAID-5. For more information, see Working with Dynamic Volumes in the chapter on Volume Management.
For detailed instructions about creating and/or managing Array Manager storage model objects, see the specific sections as follows:
RAID (Redundant Array of Independent Disks) is a collection of specifications that describe a system for ensuring the reliability and stability of data stored on large disk subsystems.
RAID provides the following general benefits:
Different RAID levels provide varying degrees of improved reliability and performance. See Choosing RAID Levels for a description of RAID levels and the advantages and disadvantages between them.
RAID provides various features to ensure high availability of data in the event of drive failure. These features include data duplication and disk drive rebuilding.
RAID defines a collection of different configuration levels (RAID levels), which are used to configure an array of disks. The following illustrations shows how RAID levels (RAID 0, RAID 1, RAID-5, and RAID 10) provide various levels of performance and redundancy. From these, you can understand what choices are applicable to your particular situation.
RAID functions can be implemented with either hardware RAID (a specific RAID controller) or with software RAID (software without the specific hardware).
Software RAID can be configured on top of the hardware RAID volumes and provide a powerful variety of features. For example, you can mirror a pair of hardware RAID-5 volumes across two RAID controllers to provide better RAID controller redundancy.