HP Microsoft Windows Server 2003 for Itanium-based Systems manual RAID RAID 6 ADG

Page 64

and Qx,y in the figure), allowing data to still be preserved if two drives fail. Each set of parity data uses a capacity equivalent to that of one of the constituent drives.

This method is most useful when data loss is unacceptable but cost is also an important factor. The probability that data loss will occur when an array is configured with RAID 6 (ADG) is less than it would be if it was configured with RAID 5.

Advantages:

•This method has a high read performance.

•This method allows high data availability—Any two drives can fail without loss of critical data.

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

Disadvantages:

The main disadvantage of RAID 6 (ADG) is a relatively low write performance (lower than RAID 5) because of the need for two sets of parity data.

Comparing the hardware-based RAID methods

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

Item

RAID 0

RAID 1+0

RAID 5

RAID 6 (ADG)

 

 

 

 

 

Alternative name

Striping (no

Mirroring

Distributed

Advanced

 

fault

 

Data

Data

 

tolerance)

 

Guarding

Guarding

 

 

 

 

 

Formula for number of drives

n

n/2

n-1

n-2

usable for data (n = total number

 

 

 

 

of drives in array)

 

 

 

 

Fraction of drive space usable*

100%

50%

67% to 93%

50% to 96%

 

 

 

 

 

Minimum number of physical

1

2

3

4

drives

 

 

 

 

 

 

 

 

 

Tolerates failure of one physical

No

Yes

Yes

Yes

drive

 

 

 

 

 

 

 

 

 

Drive arrays and fault-tolerance methods 64

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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 sectionSetting the execution mode for Microsoft Windows Overview for using ACUComparison 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 screenUsing Standard Configuration mode Configuring a new controllerPossible 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 a configuration using Standard Configuration mode Modifying an existing configurationChoices available after opening ACU Modifying a configuration using Express mode Modifying a configuration using the Configuration wizardsClear Configuration Click Express Configuration, and then click BeginClick Controller Settings, and then click Begin Controller settingsCreate an array Create a logical drive Delete arrays Expand Array Delete logical drivesClick 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 Overview of the ACU CLI Using the Command Line InterfaceRunning the CLI Command variable CLI syntaxKeyword abbreviations Target variableTypical procedures Example commandHiding warning prompts Querying a deviceSample scenario SyntaxModifying the controller chassis name Example commandsExample 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 Expand Priority setting Changing the Rebuild Priority settingChanging the controller cache ratio Re-enabling a failed logical drive Changing the surface scan delay timeEnabling 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 methods Advantages RAID 0-No fault tolerance Disadvantages 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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