Compaq External RAID Controller & Subsystem Infortrend, Руководство по эксплуатации

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Functional Description
1-12
1.7 Logical Volume (Multi-Level RAID)
What is a logical volume?
Figure 1 - 15 Logical Volume
Logical
Volume
Logical
Drive
Logical
Drive
Logical
Drive
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Physical Drives
Physical Drives
Physical Drives
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.