Compaq EK-SMCPO-UG. C01 manual Diagram of a RAID 4 write

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RAID Array Controller 2-17

RAID 4

RAID 4 breaks up host data into chunks, calculates parity by performing an exclusive-or on the chunks, and then writes the chunks to all but one drive in the array and the parity data to the last drive. When the host requests data from the disk drives, the controller retrieves the chunks containing the addressed data, reconstitutes the data from the chunks, and passes the data to the host.

Figure 2-7. Diagram of a RAID 4 write

In the event of a single drive failure, a RAID 4 array will continue to operate in degraded mode. If the failed drive is a data drive, writes will continue as normal, except no data will be written to the failed drive. Reads will reconstruct the data on the failed drive by performing an exclusive-or operation on the remaining data in the stripe and the parity for that stripe. If the failed drive is a parity drive, writes will occur, as normal except no parity will be written. Reads will simply retrieve data from the data disks. There will be no deterioration in controller performance while a RAID set is in degraded mode.

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Contents Compaq StorageWorks Page Contents RAID Array Controller List of Figures RAID 0 write List of Tables Page About This Guide Maintenance Related Documents Text Conventions Symbols in Text This is a test Rack Stability Compaq Website Product Description Product OverviewRAID Array 3000 pedestal enclosure drives optional RA3000 pedestal subsystem with one controller, 230 Compaq Part NoPedestal Cabinet Pedestal FeaturesPedestal front panel major components Pedestal Components StorageWorks Building Blocks SBBsRAID Array Controller UPS Pedestal Power SuppliesEMU circuit board location Environmental Monitor Unit EMUShows the Pedestal rear panel components UltraSCSI Buses UltraSCSI bus port and default Scsi ID assignmentsUltraSCSI bus configuration switch Connecting the Pedestal to a Host System ItemÂDescription Single Host, Single Adapter CablingDescription Single Host, Dual Adapter/Dual Controller CablingHost System Dual Host, Single Adapter/Single Controller Cabling Pedestal Technical Specifications SpecificationsPower Specifications Pedestal Physical and Power SpecificationPhysical Specifications DimensionController Overview RAID Array ControllerPage Bridging the gap between the host and the pedestal Controller FeaturesUnits created from storagesets, partitions, and disk drives Specifications Controller SpecificationsController Specifications Name Controller Reset and LED IndicatorsLED/Reset Switch Interface EnvironmentalShows the front panel of the controller Flexible RAID Set ConfigurationCustom Components Performance EnhancementsWrite-Back Caching Efficient Write and Read AlgorithmsWrite On Top Write GatheringMax. No. * of Drives RAID Levels SupportedRAID Levels Supported Pedestal RAID Set RestrictionsRAID Shows a diagram of a RAID 0 write RAID 0+1 Diagram of a RAID 1 writeRAID 0+1 Example Drives SelectedFunction Diagram of a RAID 4 write Page Diagram of a RAID 5 write Just a Bunch of Drives Jbod Redundant OperationFailover EnvironmentalInitialization Message PassingResponse Backup Power ManagementResponse to Various AC Power Conditions ConditionTermination Voltage Voltage MonitoringSystem Voltage Acceptable System Voltage LevelsSupply Voltage Temperature MonitoringExternal Temperature Acceptable External Temperature LevelsAcceptable Board Temperature Levels Board TemperaturePage Maintenance Pedestal Status and Power LEDs Shows the Pedestal status LEDs SBB Status LEDsActivity LED Fault LED Indication Controller LEDsDisk Drive SBB Status LEDs EMU Error Conditions EMU Error ReportingReplacing Components FRUs Replacing an SBB Removing the Pedestal DoorReplacing an SBB Replacing a power supply Replacing a Power SupplyRemoving the controller from the pedestal Replacing the RAID Array ControllerTools required Replacing the EMU BoardRemove standoffs from UPS and external fault connectors Replacing the UPS Differential/Wide UltraSCSI BusRate Bus Length Reconfiguring the Scsi BusScsi Bus Length and External Cables Assigned Slot Device Addresses in the PedestalMaintenance Shows how to remove the screw and panel Close the side panels and replace the cover screw 11. Remove controller Replacing the Controller Memory Cache Modules12 shows how to release the locking clips 14. Install replacement Simm Expansion Pedestal Option Shows the Expansion Pedestal Expansion Pedestal CabinetExpansion Pedestal Option Expansion Pedestal Components Shows the rear panel power suppliesEMU Reconfiguring Base Pedestal UltraSCSI Bus Remove the side cover from the base pedestal Figure Disconnect Scsi cable Connect Scsi jumper Remove connector knockout plate 10. Connect Scsi cable Set the bus configuration switch to 7 Figures 4-11 13. Reconfigured Scsi bus addresses 14. Connect Scsi cable between pedestals 15. Power cable connections 16. Transfer drives from base to expansion pedestal Second Controller Option Second controller pedestal slot location Second Controller Option KitSaving Existing Configuration Installing the UpgradeUpdating Firmware Updating Firmware Using SwccFirmware update dialog box Updating Firmware Using Serial InterfaceShutting Down the RA3000 Insert Simm into connector Installing Two SIMMs into Second ControllerRemove controller from top slot Replacing Existing ControllerRestoring configuration to new controller Restoring the ConfigurationUpdating Firmware on Second Controller 10. Restored configuration exampleInstalling Original Controller Configuring the RA3000 for the Active Mode Operation Configuring the Dual Controllers Connecting to Your Dual Controller Storage System Verifying the Controller Operating Parameters