Infortrend RAID Controller Manual

2.5 Logical Volume (Multi-Level RAID)
What is a logical volume?
Figure 2 - 15 Logical Volume
Logical
Volume
Logical
Drive
….. ….. …..
Logical
Drive
Logical
Drive
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 logical volumes include:
1. Expand the MTBF (mean time between failure) by using more
redundancy drives.
2. Decrease the time to rebuild and reduce the chance of data loss
caused by multiple drive failures happening at the same time.
3. Avoid the disastrous loss of data caused by channel bus failure
with proper drive deployment.
4. Cost-efficiency.
As diagramed below, a RAID 5 logical drive consists of 24 physical
drives, and there is one drive for redundancy. By combining several
logical drives into a logical volume, the MTBF can be expanded for
that the number of the redundancy drives increases.
Functional Description 2-11