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Configuring PERC 4/Di

Dell™ PowerEdge™ Expandable RAID Controller 4/Di User's Guide

  Configuring Physical Drives

  Configuring Arrays

  Assigning RAID Levels

  Getting Information to Optimize Storage

  Planning the Array Configuration

  Deleting Logical Drives

This section describes configuration for physical drives, arrays, and logical drives, and contains tables you can complete to list the configuration for the physical drives and logical drives.

Configuring Physical Drives

Observe the following guidelines when connecting and configuring physical drives in a RAID array:

• You can place up to 20 physical drives in an array.
  
  

NOTE: The maximum number of drives you can use depends on your system configuration. With PERC 4/Di, only one single external enclosure is possible. Configurations can span the system's internal disks and external enclosure disks to support a combined maximum of 20 drives.

• All drives in an array should have the same capacity.
  
  

If the drives are not the same size, the array uses the size of the smallest drive and the same amount of space on the other drives to construct the arrays.

• 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.
  
  

Physical Device Layout

Use Table 3-1 to list the details for each physical device on the channels.

Table 3-1. Physical Device Layout Worksheet 

Device Configuration

Use Table 3-2 to list the devices that you assign to each SCSI ID for SCSI Channel 0.

Table 3-2. Current Configuration for SCSI Channel 0 Worksheet 

Use Table 3-3 to list the devices that you assign to each SCSI ID for SCSI Channel 1.

Table 3-3. Current Configuration for SCSI Channel 1 Worksheet 

Configuring Arrays

After you configure and initialize the hard drives, you are ready to configure arrays. The number of drives in an array determines the RAID levels that can be supported.

For information about the number of drives required for different RAID levels, see Table 3-5 in "Assigning RAID Levels".

Spanned Drives

You can arrange arrays sequentially with an identical number of drives so that the drives in the different arrays 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 using the RAID BIOS Configuration Utility or Dell Manager.

Hot Spares

Any hard drive that is present, formatted, and initialized but is not included in an array or logical drive can be designated as a hot spare. You can designate hard drives as hot spares using the RAID BIOS Configuration Utility or Dell Manager.

Logical Drives

Logical drives are arrays or spanned arrays that are available to the operating system. The storage space in a logical drive is spread across all the physical drives in the array or spanned arrays.

You must create one or more logical drives for each array and the logical drive capacity must include all of the drive space in an array. You can make the logical drive capacity larger by spanning arrays. In an array of drives with mixed sizes, the smallest common drive size is used and the space in larger drives is not used. PERC 4/Di supports up to 40 logical drives.

Configuration Strategies

The most important factors in RAID array configuration are:

• Drive capacity
  
  
• Drive availability (fault tolerance)
  
  
• Drive performance
  
  

You cannot configure a logical drive that optimizes all three factors, but it is easy to choose a logical drive configuration that maximizes one factor at the expense of the other two factors. For example, RAID 1(mirroring) provides excellent fault tolerance, but requires a redundant drive.

Configuring Logical Drives

After you have attached all physical drives, perform the following steps to prepare a logical drive:

1. Start the system.
   
   
2. Press <Ctrl><M> during bootup to run the RAID BIOS Configuration Utility.
   
   
3. Select Easy Configuration in the RAID BIOS Configuration Utility or select New Configuration to customize the RAID array.
   
   
4. Create and configure one or more system drives (logical drives).
   
   
5. Select the RAID level, cache policy, read policy, and write policy.
   
   
6. Save the configuration.
   
   
7. Initialize the system drives.
   
   

After initialization, you can install the operating system.

Logical Drive Configuration

Use Table 3-4 to list the details for each logical drive that you configure.

Table 3-4. Logical Drive Configuration Worksheet 

Assigning RAID Levels

Only one RAID level can be assigned to each logical drive. Table 3-5 displays the drives required for each RAID level.

Table 3-5. Physical Drives Required for Each RAID Level 

Getting Information to Optimize 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

Define the major purpose of the disk array by answering questions such as the following:

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

Planning the Array Configuration

Fill out Table 3-6 to help you plan the array configuration.

Table 3-6. Factors to Consider for Array Configuration 

Deleting Logical Drives

Your RAID controller supports the ability to delete any unwanted logical drives and use that space for a new logical drive. You can have an array with multiple logical drives and delete a logical drive without deleting the whole array.

NOTE: Refer to "Deleting Logical Drives" for the procedure.

After you delete a logical drive, you can create a new one using the configuration utilities. You can create the next logical drive from the non-contiguous free space (`holes') and from the newly created arrays.

NOTICE: Deletion of a logical drive is blocked under certain conditions: during a reconstruction, rebuild, initialization, or consistency check.

The main benefit is that after you delete any unwanted logical drives, you are not restricted to sequential or contiguous logical drives when you create new ones. You can use non-contiguous segments to create logical drives.

NOTE: Drive size expansion is not possible, even though you can use non-contiguous free space to create a new logical drive.

NOTE: You cannot move an existing logical drive to another area to protect it from defragmentation caused by logical drive deletion.

You can still create sequential logical drives, without using the non-contiguous segments. The utilities provide information about sequential segments, non-contiguous segments and physical drives that have not been configured.

Please read all restrictions and disclaimers.

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