Compaq Infortrend manual Logical Volume Multi-Level RAID

1.7Logical Volume (Multi-Level RAID)

What is a logical volume?

Figure 1 - 15 Logical Volume

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A logical volume is a combination of RAID 0 (Striping) and other RAID levels. Data written to a logical volume is first broken into smaller data segments and striped across different logical drives in a logical volume. Each logical drive then distributes data segments to its member drives according to its mirroring, parity, or striping scheme. A logical volume can be divided into a maximum of eight partitions. During normal operation, the host sees a non-partitioned logical volume or a partition of a partitioned logical volume as one single physical drive.

The benefits of using a logical volume have been achieved by:

1.Extending the MTBF (mean time between failure) by using more redundancy drives (spare drives).

2.Decreasing the time to rebuild and reducing the chance of data loss by simultaneous drive failures because drives are included in different drive groups using a multi-level logical structure.

3.Avoiding the chance of data loss by channel bus failure with flexible drive deployment.

As diagramed below, numerous drives can be included in a logical drive, and one of them is used for redundancy. By grouping these drives into several logical drives, and then into a logical volume, chance of failing two drives in a logical unit is greatly reduced. Each logical drive can have one or more local spares. A failed drive can be immediately replaced by a local spare, reducing the risk of losing data if another should fail soon afterwards.

Functional Description 1-12