Apple NMB-003 manual RAID 3 requires a minimum of three drives, Hardware and Software RAID

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RAID 3: Parallel transfer with parity on dedicated disk

RAID level 3 adds redundant information to a striped set of drives with parallel access, allowing regeneration and reconstruction in the event of a disk failure. The parity data is stored on one disk dedicated to this purpose. RAID 3 provides high transfer rates and high reliability and availability, at a lower cost than RAID levels that incorporate mirroring.

RAID 3 requires a minimum of three drives.

RAID 5: Independent data disks with distributed parity

By distributing the parity information across all drives in a set, RAID level 5 alleviates the write bottleneck intrinsic to RAID 3, and achieves high reliability and data availability. However, RAID 5 can result in asymmetrical performance—better read than write. For this reason, RAID 5 is often augmented with related storage technologies such as caching.

RAID 5 offers the highest read data transaction rate of all levels along with a medium write rate. The low ratio of ECC parity disks to data disks offers hardware efﬁciency. Disk failure has a moderate impact on the total transfer rate, and this level also incorporates the most complex controller design.

RAID 5 requires a minimum of three drives.

Preconfigured Level 5 on the Xserve RAID System

The Xserve RAID system is preconﬁgured with RAID 5. The speed and capacity of the system’s hardware and RAID controllers make this level an optimum conﬁguration for most storage needs. Apple recommends that you use this preconﬁgured RAID 5 setup.

Hardware and Software RAID

In addition to the RAID levels described above, which you create with the RAID Admin application on the CD that came with your system, you can use Apple RAID (part of Disk Utility in Mac OS X) to augment level 1, 3, or 5. These software-conﬁgured variations are known as RAID 10, 30, and 50.

RAID 10

RAID level 10 uses software to stripe data across the two controllers for redundancy or enhanced performance.

To create a RAID 10 conﬁguration, you use RAID Admin ﬁrst and Disk Utility second. See the document “Using RAID Admin and Disk Utility” on the CD that came with your system for instructions. After you’ve used Disk Utility to set RAID 10, this conﬁguration appears as one disk on the host system.

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Contents User’s Guide Apple Computer, Inc. All rights reserved Apple Computer, IncContents Connecting Xserve RAID to a Host System and a Network Installing the SystemUsing the Xserve RAID System Installing or Replacing ComponentsConnecting a 14-Drive System to a Host Computer or Switch Installing Xserve RAID Hardware and SoftwareData Storage Methods RAID OverviewAppendix B Safety, Maintenance, and Ergonomics Glossary Appendix a SpecificationsAbout This Guide Page Introducing Xserve RAID Unpacking the System Introducing Xserve RAID Your System at a Glance-Front Panel Indicates temperature status green is OK, red is failure RAID Your System at a Glance-Back PanelRedundant, hot-swappable cooling module cools the system Your System at a Glance-Mounting Hardware Use this bar to fasten extenders C and D for a deep rack Page Guidelines for Installation Preparing to Install Xserve RAID in a RackPrecautions for Handling the System Use your leg muscles to liftChoosing the System’s Location in the Rack Lift with a smooth motion don’t jerk the load up or downRack Stability Electrical PowerSecurity Operating EnvironmentMounting Xserve RAID in a Rack Getting Ready to Install the System Determine the Position for the System in the Rack Prepare the System for Installation Installing the SystemFollow the instructions in Unpacking the System on Assemble the Brackets and Extenders Two mounting screws for attaching the system to the rackTighten the screws and then remove the template Repeat this procedure for the second bracket and extender Six short screws for assembling two brackets and extenders Secure each bolt with a washer Adjust the mounting Mounting Xserve RAID in a Rack Mount the System in the Rack Secure the System in the Rack or Cabinet Moving the Xserve RAID System System and a Network Connecting Xserve RAID to a Host System or Switch Installing the Host Bus Adapter Card in the Host SystemAbout Fibre Channel Connections and Cables Connecting the System to Xserve or a Power Mac G4 Connecting Xserve RAID to a Switch or Hub Removing Cables From the Xserve RAID and Host Systems Connecting to a Network Connecting Power to the System Plug one of the system’s power cords into the UPS Connecting an Uninterruptible Power SupplyFollow these steps to connect a UPS unit to the system Starting Up the System Using the Xserve RAID SystemTurning Off the System Using Status Lights and Other IndicatorsLight manually check If the System Has a Problem Follow these steps to install or replace a drive module Installing or Replacing an Apple Drive ModuleAbout Replacing Components Security lock Follow these steps to replace a power supply Replacing a Power SupplyReplacing a Cooling Module Installing or Replacing Components Replacing a RAID Controller Module Installing or Replacing a Battery Module Obtaining Additional Replacement Components Installing the system in a rack or cabinet Setting Up the Xserve RAID SystemInstalling Xserve RAID Hardware and Software RAID OverviewAbout RAID Storage Connecting to an Ethernet networkScalability for expansion of storage How RAID WorksData Storage Methods RAID Levels RAID 0+1 requires a minimum of four drivesRAID 5 requires a minimum of three drives RAID 3 requires a minimum of three drivesHardware and Software RAID What’s Next? Planning RAID Storage For the Xserve RAID System Tools for Configuring the Xserve RAID SystemRAID Controllers and Drive Modules Drive modules Controllers RAID RAID 0+1 Xserve RAID SchemesSystem With Four Drive Modules RAID 1 Schemes RAID 3 or RAID 0+1 and RAID 10 Schemes System With Seven Drive Modules RAIDDisk Mirror Mirror Mirror Hot spare RAID 3 or 5 Hot spare RAID 3 or Disk System With 14 Drive Modules RAID 0+1 Disk Hot spare RAID 1 and RAID 3 or Disk Mirrors RAID1 Hot spare RAID RAID 30 and 50 Schemes Storage Capacities for Xserve RAID Schemes Xserve RAID Hardware Connections Connecting a 14-Drive System to a Host Computer or Switch Connecting a Four-Drive System to a Host Computer or SwitchCommon RAID Terms GlossaryPage Fibre Channel PCI Card Specifications RAID Controller SpecificationsSpeciﬁcations Dimensions and Operating Environment Apple Drive Module SpecificationsEthernet Specifications UPS Interface SpecificationsPin D connector Cooling Module Specifications Power Supply SpecificationsBattery Module Optional Information Important Safety Information Safety, Maintenance, and ErgonomicsCleaning Your Equipment Power SupplyHandling Your System Safety, Maintenance, and Ergonomics Page Complies with European Directive 89/336/EEC