Adaptec ATA II 1220SA RAID Technology Overview, Understanding Drive Segments, Stripe-unit Size

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Appendix A: Understanding RAID ● 48

RAID Technology Overview

RAID is the technology of grouping several physical drives in a computer into an array that you can define as one or more logical drives. Each logical drive appears to the operating system as a single drive. This grouping technique greatly enhances logical-drive capacity and performance beyond the physical limitations of a single physical drive.

When you group multiple physical drives into a logical drive, the HostRAID controller can transfer data in parallel from the multiple drives in the array. This parallel transfer yields data- transfer rates that are many times higher than with non-arrayed drives, enabling the system to better meet the throughput (amount of data processed in a given amount of time) or productivity needs of the multiple-user network environment.

The ability to respond to multiple data requests provides not only an increase in throughput, but also a decrease in response time. The combination of parallel transfers and simultaneous responses to multiple requests enables disk arrays to provide a high level of performance in network environments.

Understanding Drive Segments

A drive segment is a disk drive or portion of a disk drive that is used to create an array. A disk drive can include both RAID segments (segments that are part of an array) and available segments. Each segment can be part of only one logical device at a time. If a disk drive is not part of any logical device, the entire disk is an available segment.

Stripe-unit Size

With RAID technology, data is striped across an array of physical drives. This data-distribution scheme complements the way the operating system requests data.

The granularity at which data is stored on one drive of the array before subsequent data is stored on the next drive of the array is called the stripe-unit size.

You can set the stripe-unit size to 16, 32, or 64 KB. You can maximize the performance of your HostRAID controller by setting the stripe-unit size to a value that is close to the size of the system I/O requests. For example, performance in transaction-based environments, which typically involve large blocks of data, might be optimal when the stripe-unit size is set to 32 or 64 KB. However, performance in file and print environments, which typically involve multiple small blocks of data, might be optimal when the stripe-unit size is set to 16 KB.

The collection of stripe units, from the first drive of the array to the last drive of the array, is called a stripe.

Selecting a RAID Level and Tuning Performance

Disk arrays are used to improve performance and reliability. The amount of improvement depends on the application programs that you run on the server and the RAID levels that you assign to the logical drives.

Each RAID level provides different levels of fault-tolerance (data redundancy), utilization of physical drive capacity, and read and write performance. In addition, the RAID levels differ in regard to the minimum and maximum number of physical drives that are supported.

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Contents Serial ATA II 1430SA, 1420SA, 1220SA HostRAID Controllers Copyright Adaptec Customer Support Limited 3-Year Hardware Warranty Regulatory Compliance Statements Contents Installing the HostRAID Controller Disk Drives Understanding Adaptec Storage Manager Safety Information About This Guide How to Find More Information What You Need to Know Before You BeginTerminology Used in this Guide About Your HostRAID Controller HostRAID Controller Features Array Level FeaturesUpgrading the HostRAID Controller Firmware About the Adaptec 1430SA Controller About the Adaptec 1420SA Controller About the Adaptec 1220SA Controller Kit Contents System Requirements Kit Contents System RequirementsGetting Started Choosing a RAID Level Selecting Disk DrivesSelecting Cables Disk Drives for Your ControllerInstallation Options Basic Installation StepsInstalling with an Operating System Installing on an Existing Operating SystemInstalling the HostRAID Controller Disk Drives Installing the HostRAID Controller Before You BeginConnecting Disk Drives to Sata HostRAID Controllers Determining the Boot ControllerChecking Your Controller and Devices Next StepsCreating a Bootable Array Setting the Boot Controller Creating an ArrayCreating an Array with the ACU Select Express configuration..., then click Next Creating an Array with Adaptec Storage ManagerMaking Your Array Bootable Installing the Driver An Operating System Installing with Windows Creating a Driver DiskInstalling with Red Hat Linux Installing with Suse LinuxInstalling with NetWare Installing the Driver on an Existing Operating System Installing on Windows Installing on Red Hat or Suse Linux Installing on NetWareManaging Your Storage Space Installing Adaptec Storage Manager About the Hrconf Command Line UtilityAbout Adaptec Storage Manager About the ARC Utility About the AFUWhich Utility Should I Use? Understanding Adaptec Storage Manager Features OverviewChanging How Drives are Displayed Physical Devices ViewLogical Devices View Collapsed and Expanded Views Component Views Solving Problems Troubleshooting Checklist Recovering from a Disk Drive FailureFailed Disk Drive Protected by a Hot Spare Failed Disk Drive Not Protected by a Hot Spare Failure in Multiple Arrays SimultaneouslyDisk Drive Failure in a RAID 0 Array Multiple Failures in the Same ArrayUnderstanding RAID Selecting a RAID Level and Tuning Performance RAID Technology OverviewUnderstanding Drive Segments Stripe-unit SizeRAID 0 Non-RAID Arrays RAIDRAID 1 Arrays RAID 10 ArraysUsing the ARC Utility Introduction to the ARC Utility Running the ARC UtilityCreating and Managing Arrays Creating a New ArrayRAID Managing Arrays Rebuilding ArraysForce from Offline Managing Bootable Arrays and Devices Configuring Disk DrivesAdding/Deleting Hotspares Using SATASelect Atapi SupportSATASelect Options SmartFormatting and Verifying Disk Drives Using the AFU for DOS Introduction System RequirementsCompatibility Running the AFU from the Command Line Running the AFU from the GUISave Update AFU Command Line Step-by-Step Command SwitchesAfu update /C controllernumber Safety Information Electrostatic Discharge ESDTechnical Specifications Environmental Specifications DC Power RequirementsCurrent Requirements Glossary See channel Initialize See configure Mirrored array/mirroring See RAID 1, RAID Area on each disk reserved for use by the RAID controller See simple volume, spanned volume Index Scsi Adaptec, Inc
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