HP Microsoft Windows Server 2003 for Itanium-based Systems manual RAID 5-distributed data guarding

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•No data is lost when a drive fails, as long as no failed drive is mirrored to another failed drive (up to half of the physical drives in the array can fail).

Disadvantages:

•This method is expensive (many drives are needed for fault tolerance).

•Only half of the total drive capacity is usable for data storage.

RAID 5—distributed data guarding

In a RAID 5 configuration, data protection is provided by parity data (denoted by Px,y in the figure). This parity data is calculated stripe by stripe from the user data that is written to all other blocks within that stripe. The blocks of parity data are distributed evenly over every physical drive within the logical drive.

When a physical drive fails, data that was on the failed drive can be calculated from the remaining parity data and user data on the other drives in the array. This recovered data is usually written to an online spare in a process called a rebuild.

This configuration is useful when cost, performance, and data availability are equally important.

Advantages:

•Has high read performance.

•Data is not lost if one physical drive fails.

•More drive capacity is usable than with RAID 1+0—parity information requires only the storage space equivalent to one physical drive.

Disadvantages:

•Has relatively low write performance.

•Data is lost if a second drive fails before data from the first failed drive is rebuilt.

RAID 6 (ADG)—Advanced Data Guarding

NOTE: Not all controllers support RAID 6 (ADG).

RAID 6 (ADG), like RAID 5, generates and stores parity information to protect against data loss caused by drive failure. With RAID 6 (ADG), however, two different sets of parity data are used (denoted by Px,y

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Contents HP Array Configuration Utility User Guide Audience assumptions Contents Diagnosing array problems This section Features and system requirementsInstalling ACU Getting startedOverview for using ACU Setting the execution mode for Microsoft WindowsComparison of ACU execution modes Choosing an operating mode Opening ACU in Local Application modeHttp//servername2301 Opening ACU in Browser modeSelect Device Queries Opening ACU through Systems Insight ManagerGUI operating modes Typical Standard mode screenTypical Configuration Wizards mode screen Typical Express Configuration mode screen Completing the configuration processConfiguring a new controller Using Standard Configuration modePossible tasks in Standard Configuration mode Using Express Configuration mode Click Create an array, and then click Begin Using the configuration wizardsCreating an array Click FinishConfiguring a new controller Click Create a logical drive, and then click Begin Creating a logical driveConfiguring a new controller Modifying an existing configuration Modifying a configuration using Standard Configuration modeChoices available after opening ACU Click Express Configuration, and then click Begin Modifying a configuration using Express modeModifying a configuration using the Configuration wizards Clear ConfigurationController settings Click Controller Settings, and then click BeginCreate an array Create a logical drive Delete arrays Delete logical drives Expand ArrayClick Delete logical drives, and then click Begin Click Migrate a logical drive, and then click Begin Extend logical driveMigrate a logical drive Click Extend logical drive, and then click BeginClick Spare Management, and then click Begin Spare managementSelective Storage Presentation RA4x00 controllersMSA and Smart Array Cluster storage controllers Click ACU Switch Configuration Configuring switchesRecombining a split, mirrored array Splitting a mirrored arrayModifying an existing configuration Operating modes Command line syntaxScripting in ACU Introduction to scripting in ACUCpqacuxe -i Filename Sample custom input scriptDescription of option categories in ACU scripting Script file optionsMethod Control categoryController category ActionRAIDArrayID ClearConfigurationWithDataLossController LicenseKey, DeleteLicenseKeySSPState SurfaceScanDelayArray category RebuildPriority, ExpandPriorityLogicalDrive Logical Drive categoryOnlineSpare DriveArrayAccelerator SizeSectors StripeSizeHostMode Error reportingSSPAdaptersWithAccess ConnectionNameACU scripting error messages 0-9, !, @, #, *, , , ,, -, , +, , ., /, and space. The ID Current configuration Using the Command Line Interface Overview of the ACU CLIRunning the CLI Target variable Command variableCLI syntax Keyword abbreviationsQuerying a device Typical proceduresExample command Hiding warning promptsSyntax Sample scenarioExample commands Modifying the controller chassis nameExample Sample scenario Using Selective Storage PresentationManaging host modes connection profiles Modifying connection namesExtending a logical drive Deleting target devicesIdentifying devices Expanding an arrayTarget modify size=#max? forced Target modify raid=01+0156adg? ss=8163264128256default?Managing spare drives Migrating a logical driveChanging the Rebuild Priority setting Changing the Expand Priority settingChanging the controller cache ratio Changing the surface scan delay time Re-enabling a failed logical driveEnabling or disabling the drive cache Typical scenario Setting the targetEnabling or disabling the array accelerator Disabling a redundant controller= rescan Rescanning the systemFactors involved in logical drive failure Probability of logical drive failureProbability of logical drive failure Drive arrays Drive arrays and fault-tolerance methodsDrive arrays and fault-tolerance methods Hardware-based fault-tolerance methods Fault-tolerance methodsRAID 0-No fault tolerance AdvantagesDisadvantages RAID 1+0-drive mirroring RAID 6 ADG-Advanced Data Guarding RAID 5-distributed data guardingRAID RAID 6 ADG Comparing the hardware-based RAID methodsSelecting a RAID method Alternative fault-tolerance methodsPost messages Diagnosing array problemsDiagnostic tools Server DiagnosticsAcronyms and abbreviations SSP Index Index