HP AD510A HP StorageWorks 1500 Modular Smart Array installation guide (355901 - Page 27
Hard drive sizes and types, Spare drives, Array sizing (capacity), HP Array Configuration
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NOTE: For detailed information about the different RAID levels, see the HP Array Configuration Utility User Guide. This guide is available on the Documentation CD and on the Technical documentation page of the MSA1500 website: http://www.hp.com/go/msa1500cs. Hard drive sizes and types Hard drives in each enclosure and included in the same array should be the same size and type. When drive sizes and types are mixed within a storage enclosure, the usable capacity and the processing ability of the entire storage sub-system is affected. When hard drives of different types or sizes are included in the same enclosure, the processing characteristics of the entire enclosure are reduced to that of the slowest and smallest drive. When hard drives of different sizes are included in a LUN, the LUN defaults to the smallest individual drive size and capacity in the larger drives is unused. Spare drives HP recommends including spare drives in your LUNs. Spares are hard drives that are not active members of any particular LUN, but have been configured to be used in the event that a drive in one of the LUNs should fail. If a spare is present and a physical hard drive fails, the spare automatically replaces the failed drive as a member of the LUN and the process of rebuilding the information onto the spare automatically begins. The system uses the mirrored or parity information from the other member drives to reconstruct the data onto the spare. Array sizing (capacity) When planning for optimal file-serving performance, you must determine the number of hard drives necessary to maintain an optimum performance level. As a general rule, the greater the number of drives that are included in an array, the greater the performance level that can be achieved. However, the performance considerations are offset by fault tolerance considerations-the greater the number of drives in an array, the higher the probability of one or more failures in that array. HP StorageWorks 1500 Modular Smart Array installation guide 27