Understanding RAID 6 ADG for Optimal Data Protection

•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 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.

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HP Smart Storage Adstrator manual RAID 6 ADG-Advanced Data Guarding

Contents

HP Smart Storage Administrator User Guide Page Contents Optional components 130 Benefits of using HP SSA About HP SSA Support for configuration tasks Procedure HP Smart Array Array configuration Array configuration guidelines Native support for 64-bit and 32-bit operating systems Minimum requirements Accessing HP SSA in the offline environment Launching HP SSA during Post Gen8 or later Mounting the image through iLO Launching HP SSA from an ISO image all generationsBurning the image to a CD or DVD Set up PXELinux Installing the image on a PXE serverPrerequisites Configure PXELinux Specify the ISO image path Accessing HP SSA in the online environment Supported network file systems Hpssa- h Launching HP SSA on a local serverHttp//servername2301 Operations Using the HP SSA GUI Icon and key stroke legend Navigating the GUI Configure screen When a controller is selected, the following elements appear Diagnostics screen HP SSA help Configuration tasks Configuring a controller Performing a Configuration task HP SSD Smart Path Operations Rapid Parity Initialization SSD Over Provisioning Optimization Operations Changing the Spare Activation Mode Changing the Spare Management mode Operations Cache Manager Operations Enable HP SmartCache About HP SmartCache Operations Operations Installing a license key with HP SmartCache Enabling SmartCache Write-back Operations Working with mirrored arrays Splitting a mirrored array Creating a split mirror backup Recombining a split mirrored array Healing an array Setting Auto RAID Replacing an array Click Create Arrays with RAID Operations Managing FLS Setting RAID mode or HBA mode Managing modes Operations Power modes Viewing controller status Diagnostic tasks Performing a Diagnostics task Operations Using the HP SSA CLI Opening the CLI in Console mode\Program Files\hp\hpssacli\Bin\hpssacli.exe Root@localhost root# hpssacli Opening the CLI in Command mode Command variableCLI syntax Target variable Available options are Current value Default Querying a deviceHiding warning prompts = ctrl ch=Lab4 ld 1 modify raid=0 ss=? Show command Target controller show config detailKeyword abbreviations Target show detailstatus = ctrl all show Help command = ctrl ch=lab4 show configDisplaying the current versions of the application layers Version Setting the boot controller Typical proceduresSetting the boot volume Setting the target Identifying devicesSet target target = set target ctrl slot=3 = clear target Generating a diagnostic report Deleting target devicesTarget modify led=onoff Target delete forced Erasing a physical drive Rescanning the systemEntering or deleting a license key Optimizing controller performance for video Creating a logical drive Target create type=ld parameter=value Available options are +0 default value Sample scenario Target modify newarray= Moving a logical driveTarget modify drives=# ##,# ##,# ##-# ## Viewing enclosure information Viewing SSD physical drivesViewing SSD information SmartCache in Hpssacli Rapid Parity Initialization methods SSD Over Provisioning OptimizationAssigning a chassis name to the controller = ctrl slot=1 array B create type=ldcache datald=2 Setting the spare activation mode Managing spare drivesTarget modify spareactivationmode= failure predictive Controller slot=1 modify spareactivationmode=predictive Expanding an array Spare Management Mode in HpssacliShrinking an array Target remove drives=###-### Moving an arrayTarget modify drives=###-### spares=###-### = ctrl slot=1 create type=arrayr0 drives=allunassigned Extending a logical driveTarget modify size=#max? forced Setting the preferred path mode Target modify raid=01+0156adg? ss=8163264128256default?Migrating a logical drive Target modify preferredpathmode=automaticmanual? Disabling a redundant controller Changing the Rebuild Priority settingAssigning a redundant controller to a logical drive Changing the Expand Priority setting Setting the surface scan modeChanging the surface scan delay time Re-enabling a failed logical drive Enabling or disabling the drive cache Changing the controller cache ratioEnabling or disabling the array accelerator Enabling a script to exit on error Using the Split Mirror commandSet exitonerror=enable set eoe=disable Show exitonerror Enabling SmartCache Write-back HBA mode Target modify latency=lowhighdisable?Controller slot=5 modify latency=low Target modify hbamode=onoff? Power mode Using HP SSA scriptingRAID mode Capturing a configuration Using an Input scriptCreating an HP SSA script file Hpssascripting -c Filename -internal -external -e Filename Script file requirements Sample custom input script Sample custom capture script Date captured Wed Jan 15 153314 Version Initial encryption configuration Sample encryption script Encryption configuration PlainText= Enable Script file options Action mode Method modeControl category Controller category Controller ClearConfigurationWithDataLossCacheState DPOEnable ElevatorSortEnableIRPEnable DriveWriteCache MNPDelay NoBatteryWriteCachePower modes LicenseKey, DeleteLicenseKey SurfaceScanDelay SurfaceScanDelayExtendedQueueDepth RapidParityInitialization DPOEnable = No ElevatorSortEnable = Yes IRPEnable = No Array categoryArray ArrayR0 CachingArray DriveDriveType OnlineSpareMode OnlineSpare Logical Drive categorySplitMirror LogicalDrive ArrayAcceleratorCachingLogicalDrive NumberOfParityGroups CachedLogicalDrivePreferredPath SetBootVolumePrimary SetBootVolumeSecondaryRenumber Repeat Size SizeBlocksSmartCache Write-back StripSize Encryption support commands Encryption controller category ControllerPasswordMode Remove Suspend Resume Encryption logical volume category EncryptionRecoveryQuestion XML output XML support\hpssascripting -c out.xml XML input XML input file DTD HP SSA scripting warning messages Comment or clarification Code HP SSA scripting error messages Error code Error message Comment or clarification This error can occur when you attempt to add or Or logical drive Free space for the requested size 3011 Expand array and changed the size or RAID level ACCEPTEULA=YES About the utility HP Smart Storage Administrator Diagnostics Utility CLIReported information Troubleshooting Installing the utility Field Description Diagnostic report procedures Launching the utility in CLI modeSmartSSD Wear Gauge report procedures Drive arrays and fault-tolerance methods 512e Physical drive supportDrive arrays Identifying and viewing SmartSSD Wear Gauge report files Troubleshooting Troubleshooting Fault-tolerance methods Effects of a hard drive failure on logical drives RAID 0-No fault tolerance RAID 1 and RAID 1+0 RAID Troubleshooting RAID 1 ADM and RAID 10 ADM RAID 5-distributed data guarding RAID 6 ADG-Advanced Data Guarding RAID Comparing the hardware-based RAID methods Alternative fault-tolerance methods Selecting a RAID method Diagnostic tools Diagnosing array problemsTroubleshooting resources Troubleshooting Optional components HP Secure Encryption HP Smart Array Advanced Pack About Saap Acronyms and abbreviations ILO PXE Documentation feedback Index HP Smart Storage Administrator Diagnostics Utility XML DTD