User Guide

Configuration: PowerEdge Expandable RAID Controller 2/SC

Configuring SCSI Physical Drives | Configuring Arrays | Configuration Strategies | Assigning RAID Levels | Configuring Logical Drives | Optimizing Data Storage

Configuring SCSI Physical Drives

SCSI Channel

Physical SCSI drives must be organized into logical drives. The arrays and logical drives that you construct must be able to support the RAID level that you select. Your PowerEdge Expandable RAID Controller 2/SC (hereafter referred to as "PERC 2/SC") has one SCSI channel.

Basic Configuration Guidelines

You should observe the following guidelines when connecting and configuring SCSI devices in a RAID array:

• Place a maximum of 8 physical disk drives in an array.
• Include all drives that have the same capacity in the same array.
• Make sure any hot spare has a capacity that is at least as large as the largest drive that may be replaced by the hot spare.
• When replacing a failed drive, make sure that the replacement drive has a capacity that is at least as large as the drive being replaced.

Configuring Arrays

Organize the physical disk drives in arrays after the drives are connected to PERC 2/SC, formatted, and initialized. Each array can consist of 1 to 8 physical disk drives.

PERC 2/SC supports up to 8 arrays. The number of drives in a array determines the RAID levels that can be supported.

Arranging Arrays

You must arrange the arrays to provide additional organization for the drive array. You must arrange arrays so that you can create system drives that can function as boot devices.

You can sequentially arrange arrays with an identical number of drives so that the drives in the group are spanned. Spanned drives can be treated as one large drive. Data can be striped across multiple arrays as one logical drive.

You can create spanned drives by using the PERC 2/SC BIOS Configuration Utility or the PERC 2/SC Configuration Manager.

Creating Hot Spares

Any drive that is present, formatted, and initialized but not included in an array or logical drive is automatically designated as a hot spare.

You can also designate drives as hot spares via PERC 2/SC BIOS Configuration Utility, Configuration Manager, or Console.

Creating Logical Drives

Logical drives are arrays or spanned arrays that are presented to the operating system. You must create one or more logical drives.

The logical drive capacity must include all of the disk space in an array. In an array with drives of mixed sizes, the smallest common size is used and larger disk drives are truncated. The logical drive capacity can also be larger than an array by using spanning. PERC 2/SC supports up to 8 logical drives.

Configuration Strategies

The most important factors in RAID array configuration are drive capacity, drive availability (fault tolerance), and drive performance. You cannot configure a logical drive that optimizes all 3 factors, but you can to choose a logical drive configuration that maximizes 1 factor at the expense of the other 2 factors.

Maximizing Capacity

RAID 0 achieves maximum drive capacity, but does not provide data redundancy. Maximum drive capacity for each RAID level is shown in the following table.

Maximizing Drive Availability

You can maximize the availability of data on the physical disk drive in the logical array by maximizing the level of fault tolerance. The levels of fault tolerance provided by the RAID levels are:

Maximizing Drive Performance

You can configure an array for optimal performance. But optimal drive configuration for one type of application will probably not be optimal for any other application.

Assigning RAID Levels

Only one RAID level can be assigned to each logical drive.

Configuring Logical Drives

After you have installed the PERC 2/SC in the server and have attached all physical disk drives, follow these steps to prepare a RAID disk array:

1. Optimize the PERC 2/SC options for your system. See the PowerEdge Expandable RAID Controller 2/SC User's Guide for additional information.
2. Press <Ctrl> <m> to run the PERC 2/SC Configuration Manager.
3. Define and configure 1 or more logical drives. Select Easy Configuration in the BIOS Configuration Utility or select New Configuration to customize the RAID array.
4. Create and configure 1 or more system drives (logical drives). Select the RAID level, cache policy, read policy, and write policy.
5. Save the configuration.
6. Initialize the system drives. After initialization, you can install the operating system.

Optimizing Data Storage

Data Access Requirements

Each type of data stored in the disk subsystem has a different frequency of read and write activity. If you know the data access requirements, you can more successfully determine a strategy for optimizing the disk subsystem capacity, availability, and performance.

Servers that support video-on-demand typically read the data often, but write data infrequently. Both the read and write operations tend to be long. Data stored on a general-purpose file server involves relatively short read and write operations with relatively small files.

Array Functions

You must first define the major purpose of the disk array. Will the disk array increase the system storage capacity for general-purpose file and print servers? Does the disk array support any software system that must be available 24 hours per day? Will the stored information contain large audio or video files that must be available on demand? Will the disk array contain data from an imaging system?

You must identify the purpose of the data to be stored in the disk subsystem before you can confidently choose a RAID level and a RAID configuration.