Compaq EK-SMCPO-UG. C01 manual Diagram of a RAID 5 write

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RAID Array Controller 2-19

RAID 5

RAID 5 addresses the bottleneck issue for barrages of widely scattered, small I/O operations. Like RAID 4, RAID 5 breaks up data into chunks, calculates parity, and then writes the chunks in stripes to the disk drives; saving one drive one each stripe for the parity data. Unlike RAID 4, however, RAID 5 changes the parity drive on each stripe. This means, for instance, that a write operation involving drive 2 on stripe 1 can conceivably take place at the same time as a write involving drive 3 on stripe 2, since they would be addressing different parity drives. Figure 2-5 shows a diagram of a RAID 5 write.

Figure 2-8. Diagram of a RAID 5 write

RAID 5 handles drive failures in the same manner as RAID 4, except the parity is different for each stripe. The controller either uses the parity information on a stripe to reconstruct its data or simply reads the data as normal, depending on the location of the stripe’s parity drive.

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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 RAID Array Controller Pedestal ComponentsStorageWorks Building Blocks SBBs 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 SpecificationsPhysical Specifications Pedestal Physical and Power SpecificationDimension Power SpecificationsController 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 LED/Reset Switch Interface Controller Reset and LED IndicatorsEnvironmental NameShows the front panel of the controller Flexible RAID Set ConfigurationCustom Components Performance EnhancementsWrite-Back Caching Efficient Write and Read AlgorithmsWrite On Top Write GatheringRAID Levels Supported RAID Levels SupportedPedestal RAID Set Restrictions Max. No. * of DrivesRAID Shows a diagram of a RAID 0 write RAID 0+1 Diagram of a RAID 1 writeFunction RAID 0+1 ExampleDrives Selected Diagram of a RAID 4 write Page Diagram of a RAID 5 write Just a Bunch of Drives Jbod Redundant OperationInitialization EnvironmentalMessage Passing FailoverResponse to Various AC Power Conditions Backup Power ManagementCondition ResponseSystem Voltage Voltage MonitoringAcceptable System Voltage Levels Termination VoltageExternal Temperature Temperature MonitoringAcceptable External Temperature Levels Supply VoltageAcceptable Board Temperature Levels Board TemperaturePage Maintenance Pedestal Status and Power LEDs Shows the Pedestal status LEDs SBB Status LEDsDisk Drive SBB Status LEDs Activity LED Fault LED IndicationController 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 BusScsi Bus Length and External Cables Reconfiguring the Scsi BusAssigned Slot Device Addresses in the Pedestal Rate Bus LengthMaintenance 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