Adaptec 133U2 User Guide - Page 139
RAID 0 Arrays, RAID 1 Arrays
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Managing Arrays and Spares The array management software and firmware support RAID 0, RAID 1, RAID 0/1, and RAID 5 arrays. The advantages, disadvantages, and requirements of these RAID levels are as follows: RAID 0 Arrays Maximum Disks Allowed: 161 (or as allowed by your controller) Minimum Disks Allowed: 12 In a RAID 0 array, data is distributed, or striped, across the disks in the array. The capacity of the array is approximately equal to the combined capacity of the physical disks. The I/O performance of a RAID 0 array is much better than that of a single physical disk because multiple reads and writes can be handled in parallel and because when large files are accessed the striped data is retrieved simultaneously from several disks. RAID 0 arrays do not store redundant data and therefore are not true RAID applications. If one disk fails, the entire array fails and all data is lost. This means that the fault tolerance of a RAID 0 array is less than that of any single disk in the array. The term RAID 0 is widely used for these arrays, however, because they are conceptually similar to true RAID applications. RAID 1 Arrays Maximum Disks Allowed: 2 Minimum Disks Allowed: 2 RAID 1 arrays use a single pair of disks. They are called mirrored arrays because both disks in the pair contain the same data. When data is written to a RAID 1 array it is written to each disk in the pair. The read performance of a RAID 1 array can be much better than that of a single disk, while the write performance is slightly worse. Mirrored arrays are highly reliable because the data is still safe if one disk in the pair fails. They are more costly, however, because you get only one disk of actual storage capacity from the pair of disks. 1 If the system has a single SCSI channel, the maximum would be 15 disks since no more than 15 drives could be installed in the system. 2 One-disk RAID 0 arrays are used only to control the virtual device order of single disks. 10-15
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