HP Microsoft Windows Server 2003 for Itanium-based Systems manual Fault-tolerance methods

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logical drive, the term array is often used as a synonym for logical drive. However, an array can contain several logical drives, each of a different size.

Each logical drive in an array is distributed across all of the physical drives within the array. A logical drive can also extend across more than one port on the same controller, but it cannot extend across more than one controller.

Drive failure, although rare, is potentially catastrophic. For arrays that are configured as shown in the previous figure, failure of any physical drive in the array causes every logical drive in the array to suffer irretrievable data loss. To protect against data loss due to physical drive failure, logical drives are configured with fault tolerance ("Fault-tolerance methods" on page 60).

For any configuration except RAID 0, further protection against data loss can be achieved by assigning a drive as an online spare (or hot spare). This drive contains no data and is connected to the same controller as the array. When any other physical drive in the array fails, the controller automatically rebuilds information that was originally on the failed drive to the online spare. The system is thus restored to full RAID-level data protection, although it now no longer has an online spare. (However, in the unlikely event that another drive in the array fails while data is being rewritten to the spare, the logical drive will still fail.)

When you configure an online spare, it is automatically assigned to all logical drives in the same array. Additionally, you do not need to assign a separate online spare to each array. Instead, you can configure one hard drive to be the online spare for several arrays if the arrays are all on the same controller.

Fault-tolerance methods

Several fault-tolerance methods exist. Those most often used with Smart Array controllers are hardware- based RAID methods.

Two alternative fault-tolerance methods that are sometimes used are also described ("Alternative fault- tolerance methods" on page 65). However, hardware-based RAID methods provide a much more robust and controlled fault-tolerance environment, so these alternative methods are seldom used.

Hardware-based fault-tolerance methods

HP recommends the following hardware-based methods for use with Smart Array controllers:

•RAID 0—Data Striping only (no fault tolerance)

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Contents HP Array Configuration Utility User Guide Audience assumptions Contents Diagnosing array problems Features and system requirements Installing ACUGetting started This sectionOverview for using ACU Setting the execution mode for Microsoft WindowsComparison of ACU execution modes Opening ACU in Local Application mode Choosing an operating modeOpening ACU in Browser mode Http//servername2301Opening ACU through Systems Insight Manager Select Device QueriesTypical Standard mode screen GUI operating modesTypical Configuration Wizards mode screen Completing the configuration process Typical Express Configuration mode screenConfiguring a new controller Using Standard Configuration modePossible tasks in Standard Configuration mode Using Express Configuration mode Using the configuration wizards Creating an arrayClick Finish Click Create an array, and then click BeginConfiguring a new controller Creating a logical drive Click Create a logical drive, and then click BeginConfiguring a new controller Modifying an existing configuration Modifying a configuration using Standard Configuration modeChoices available after opening ACU Modifying a configuration using Express mode Modifying a configuration using the Configuration wizardsClear Configuration Click Express Configuration, and then click BeginController 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 Extend logical drive Migrate a logical driveClick Extend logical drive, and then click Begin Click Migrate a logical drive, and then click BeginSpare management Selective Storage PresentationRA4x00 controllers Click Spare Management, and then click BeginMSA and Smart Array Cluster storage controllers Configuring switches Click ACU Switch ConfigurationSplitting a mirrored array Recombining a split, mirrored arrayModifying an existing configuration Command line syntax Scripting in ACUIntroduction to scripting in ACU Operating modesSample custom input script Cpqacuxe -i FilenameScript file options Description of option categories in ACU scriptingControl category Controller categoryAction MethodClearConfigurationWithDataLoss ControllerLicenseKey, DeleteLicenseKey RAIDArrayIDSurfaceScanDelay Array categoryRebuildPriority, ExpandPriority SSPStateLogical Drive category OnlineSpareDrive LogicalDriveSize SectorsStripeSize ArrayAcceleratorError reporting SSPAdaptersWithAccessConnectionName HostModeACU scripting error messages 0-9, !, @, #, *, , , ,, -, , +, , ., /, and space. The ID Current configuration Using the Command Line Interface Overview of the ACU CLIRunning the CLI Command variable CLI syntaxKeyword abbreviations Target variableTypical procedures Example commandHiding warning prompts Querying a deviceSample scenario SyntaxExample commands Modifying the controller chassis nameExample Using Selective Storage Presentation Sample scenarioModifying connection names Managing host modes connection profilesDeleting target devices Identifying devicesExpanding an array Extending a logical driveTarget modify raid=01+0156adg? ss=8163264128256default? Managing spare drivesMigrating a logical drive Target modify size=#max? forcedChanging 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 Setting the target Enabling or disabling the array acceleratorDisabling a redundant controller Typical scenarioRescanning the system = rescanProbability of logical drive failure Factors involved in logical drive failureProbability of logical drive failure Drive arrays and fault-tolerance methods Drive arraysDrive arrays and fault-tolerance methods Fault-tolerance methods Hardware-based fault-tolerance methodsRAID 0-No fault tolerance AdvantagesDisadvantages RAID 1+0-drive mirroring RAID 5-distributed data guarding RAID 6 ADG-Advanced Data GuardingComparing the hardware-based RAID methods RAID RAID 6 ADGAlternative fault-tolerance methods Selecting a RAID methodDiagnosing array problems Diagnostic toolsServer Diagnostics Post messagesAcronyms and abbreviations SSP Index Index
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