EVMS User Guide
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C.1. Creating an MD region

There are four EVMS MD region plug-ins: Linear, RAID-0, RAID-1, and RAID-4/5. The RAID-4/5 region plug-in provides support for both RAID-4 and RAID-5 arrays. After an MD region manager is selected, the software provides a list of acceptable objects. The ordering of the MD array is implied by the order in which you pick objects from the provided list. The following are MD region configuration options:

chunk size

The smallest chunk size is 4 KB and the largest is 4096 KB. The chunk size is a power of 2 of the previous value. Consider the intended use of the MD region when selecting chunk size. For example, if the MD region contains mostly large files, you might see better performance by having a larger chunk size. The block size of the file system being used is also an importnat factor when selecting chunk size.

This option is available for use with RAID-0 and RAID-4/5.

spare disk

The benefit of having a spare disk is that when an active disk fails, the kernel MD code automatically replaces the failed disk with the spare disk. Otherwise, the MD array operates in a degraded mode.

This option is available for use with RAID-1 and RAID-4/5.

RAID-5 algorithms

There are four RAID-5 parity algorithms: left assymetric, right assymetric, left symmetric, and right symmetric. The ACCS web page provides examples of what the different parity algorithms do.

This option is available for use with the RAID-5 algorithm.

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