Areca ARC-1120, ARC-1110, ARC-1130, ARC-1231ML/1261ML/1280ML manual RAID 1E

INTRODUCTION

1.7.3 RAID 1E

RAID 1E is a combination of RAID 0 and RAID 1, combing strip- ping with disk mirroring. RAID Level 1E combines the fast per- formance of Level 0 with the data redundancy of Leve1 1. In this configuration, data is distributed across several disk drives, similar to Level 0, which are then duplicated to another set of drive for data protection. RAID 1E has been traditionally imple- mented using an even number of disks, some hybrids can use an odd number of disks as well. Illustration is an example of a hy- brid RAID 1E array comprised of five disks; A, B, C, D and E. In this configuration, each strip is mirrored on an adjacent disk with wrap-around. In fact this scheme - or a slightly modified version of it - is often referred to as RAID 1E and was originally proposed by IBM. When the number of disks comprising a RAID 1E is even, the striping pattern is identical to that of a traditional RAID 1E, with each disk being mirrored by exactly one other unique disk. Therefore, all the characteristics for a traditional RAID 1E apply to a RAID 1E when the latter has an even number of disks. Areca RAID 1E offers a little more flexibility in choosing the number of disks that can be used to constitute an array. The number can be even or odd.

1.7.4 RAID 3

RAID 3 provides disk striping and complete data redundancy though a dedicated parity drive. RAID 3 breaks up data into smaller blocks, calculates parity by performing an exclusive-or on the blocks, and then writes the blocks to all but one drive in

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