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Configuring PERC 4

Dell™ PowerEdge™ Expandable RAID Controller 4/SC and 4/DC User's Guide

  Configuring SCSI Physical Drives

  Physical Device Layout

  Device Configuration

  Setting Hardware Termination

  Configuring Arrays

  Assigning RAID Levels

  Optimizing Data Storage

  Deleting Logical Drives

This section describes how to configure for physical drives, arrays, and logical drives. It contains tables you can complete to list the configuration for the physical drives and logical drives. This section covers the following topics:

• Guidelines for connecting and configuring SCSI devices
  
  
• Array creation
  
  
• Hot spares
  
  
• Configuration strategies
  
  
• Logical drive configuration
  
  
• Array configuration planner
  
  
• Logical drive deletion
  
  

Configuring SCSI Physical Drives

Your SCSI hard drives must be organized into logical drives in an array and must be able to support the RAID level that you select.

Observe the following guidelines when connecting and configuring SCSI devices in a RAID array:

• Include all drives that have the same capacity in the same array. 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 smallest hard drive in a logical drive (the additional space of a larger hard drive would be wasted).
  
  
• When replacing a failed hard drive, make sure that the replacement drive has a capacity that is the same size or larger than the smallest drive in a logical drive that supports redundancy (RAID 1, 5, 10, and 50).
  
  

Physical Device Layout

Use Table 4-1 to list the details for each physical device on the channels.

Table 4-1 Physical Device Layout 

Device Configuration

The following contains tables you can fill out to list the devices assigned to each channel. The PERC 4/SC controller has one channel and the PERC 4/DC has two.

Use Table 4-2 to list the devices that you assign to each SCSI ID for SCSI Channel 0.

Table 4-2 Configuration for SCSI Channel 0 

Use Table 4-3 to list the devices that you assign to each SCSI ID for SCSI Channel 1.

Table 4-3 Configuration for SCSI Channel 1

Setting Hardware Termination

If you are using the PERC 4/DC for clustering, then you must use hardware termination. Otherwise, software termination is usually OK.

• J5 Termination Enable is a three-pin header that specifies control of the SCSI termination for channel 0.
  
  
• J6 Termination Enable is a three-pin header that specifies control of the SCSI termination for channel 1.
  
  

To enable hardware termination, leave the pins open. The default is hardware termination.

Configuring Arrays

Organize the physical drives into arrays after the drives are connected to the RAID controller, formatted, and initialized. An array can consist of up to 28 physical drives (24 drives when used with the span feature in a RAID 50 configuration).

The number of drives in an array determines the RAID levels that can be supported. PERC 4 supports up to 40 logical drives per controller.

Creating Hot Spares

Any drive that is present, formatted, and initialized, but not included in an array or logical drive can be designated as a hot spare. You can use the RAID management utilities to designate drives as hot spares. The utilities are described in RAID Management Utilities.

Creating Logical Drives

Logical drives are arrays or spanned arrays that are presented to the operating system. In an array with hard drives of different sizes, the smallest size is used and larger hard drives are truncated. The logical drive capacity can also be larger than an array by using spanning. PERC 4 supports up to 40 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 three factors, but it is easy to select a logical drive configuration that maximizes one or two factors at the expense of the other factors.

Configuring Logical Drives

After you have installed the PERC 4 controller in the server and have attached all physical drives, perform the following steps to prepare a RAID disk array:

1. Start the system.
   
   
2. Press <Ctrl><M> during bootup to run the BIOS Configuration Utility or <Ctrl><H> to run the WebBIOS Configuration Utility.
   
   
3. Select Easy Configuration, New Configuration, or View/Add Configuration in PERC 4 BIOS Configuration Utility, 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.
   
   

See Initializing Logical Drives for initialization procedures. After initialization, you can install the operating system.

Logical Drive Configuration

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

Table 4-4 Logical Drive Configuration

Assigning RAID Levels

Only one RAID level can be assigned to each logical drive. Table 4-5 shows the drives required.

Table 4-5 Physical Drives Required for Each RAID Level

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 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.

Summary of RAID Levels

RAID 0 uses striping to provide high data throughput, especially for large files in an environment that does not require fault tolerance.

RAID 1 uses mirroring and is good for small databases or other applications that require small capacity, but complete data redundancy.

RAID 5 provides high data throughput, especially for small random access. Use this level for any application that requires high read request rates, but low write request rates, such as transaction processing applications. Write performance is significantly lower for RAID 5 than for RAID 0 and RAID 1.

RAID 10 consists of striped data across mirrored drives. It provides high data throughput and complete data redundancy, but requires twice as many hard drives as all other RAID levels except RAID 1.

RAID 50 uses parity and disk striping and works best with data that requires high reliability, high request rates, high data transfers, and medium-to-large capacity. Write performance is limited to the same as RAID 5.

Deleting Logical Drives

The controller supports array deletion, which is the ability to delete any unwanted logical drives and use that space for a new logical drive.

After you delete a logical drive, you can create a new one. You can use the configuration utilities to 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 the following conditions: During a reconstruction. During a rebuild, initialization or check consistency of a logical drive, if that drive has a higher logical drive number than the drive you want to delete.

After the system completes the reconstruction, rebuild, initialization, or check consistency, you can delete the logical drive.

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

NOTE: Drive size extension 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 random 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. You can use this information when you create logical drives.

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