Adaptec ATA II 1220SA Installation And User Manual

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Adaptec ATA II 1220SA Installation And User Manual Manual pdf 49 page image

Appendix A: Understanding RAID ● 49When selecting a RAID level for your system, consider the following factors.Physical drive utilization, read performance, and write performance depend on the number ofdrives in the array. Generally, the more drives in the array, the better the performance.RAID 0 (Non-RAID Arrays)An array with RAID 0 includes two or more disk drives (maximum twelve) and provides datastriping, where data is distributed evenly across the disk drives in equal-sized sections.RAID 0 arrays do not maintain redundant data, so they offer no data protection. However,compared to an equal-sized group of independent disks, a RAID 0 array provides improvedI/O performance.Drive segment size is limited to the size of the smallest disk drive in the array. For instance, anarray with two 250 GB disk drives and two 400 GB disk drives can create a RAID 0 drivesegment of 250 GB, for a total of 1000 GB for the volume, as shown in the following figure.RAIDLevelDataRedundancyPhysicalDriveCapacityUtilizationReadPerformanceWritePerformanceBuilt-InSpare DriveMin Numberof DrivesMax Numberof Drives0 No 100% Superior Superior No 1 41 Yes 50% Very high Very high No 2 210 Yes 50% Very high Very high No 4 4Disk Drive 1Disk Drive 2Disk Drive 3Disk Drive 4250 GB250 GB400 GB400 GBDisk Drives in Logical DriveDisk Drive 1Disk Drive 2Disk Drive 3Disk Drive 4RAID 0 Logical Drive = 1000 GB1234Not UsedNot Used5678 1000999998997............Unused Space: 150 GBUnused Space: 150 GBDrive Segment Size (Smallest Disk Drive)