RAID 1E (Data Mirroring and Striping)
RAID 1E uses a combination of data mirroring and striping (RAID 0) techniques. A minimum of three physical disks are required to create a RAID 1E virtual disk/array, as shown in Figure 1. RAID 1E is similar to RAID 10, except that RAID 1E operates on an odd number of disks.
Table 1 describes RAID 1E across a number of parameters.
Parameter |
Rating |
Description |
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Read Performance |
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RAID 1E provides read performance comparable to RAID 0 (striping). |
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Write Performance |
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RAID 1E provides write performance comparable to RAID 1 (disk mirroring). Write performance is comparatively lower than read performance because data (original and mirror) is written on two physical disks simultaneously. |
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Fault Tolerance |
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In a RAID 1E, mirrored data is distributed such that the array can tolerate the failure of one physical disk. When the minimum three physical disks are used in a RAID 1E virtual disk/array, approximately 33% (one physical disk) of the combined disk capacity is used for storing mirror data. In other words, RAID 1E can be rebuilt if 33% of the disks fail. As the number of disks increases, the reliability of the RAID 1E virtual disk/array decreases (lesser than 33%). Note: The reliability (as measured by Mean Time Between Failure or Mean Time To Failure) for physical disks is equal to average reliability of each disk divided by the number of disks. Assuming that each physical disk is almost perfectly reliable, the reliability is roughly inversely proportional to the number of disks. In other words, as the number of physical disks increases, the reliability of the RAID 1E virtual disk/array decreases. |
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Efficient use of disk capacity |
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Like RAID 1, RAID 1E uses the mirroring technique for fault tolerance, using 50% of the combined disk capacity for mirroring data. For example, three 100 GB physical disks (a total of 300 GB) create a 150 GB virtual disk/array because the remaining 150 GB is used to store mirror data. |
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Automatic rebuild |
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Available. |
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Minimum number of drives |
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3 Note: RAID 1E operates only on an odd number of disks. |
Figure 1 describes RAID 1E.
Figure 1 RAID 1E: Illustration
Figure 2 shows a Flash® demo of RAID 1E.
Note: To view the Flash® demo for RAID 1E, install the latest version of Adobe Flash Player at http://get.adobe.com/flashplayer/