Chapter 6: Modifying Your Direct Attached Storage
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Understanding Logical Drives
A logical drive is a group of physical disk drives that appears to your operating system as a
single drive that can be used for storing data.
A logical drive can comprise one or more disk drives and can use part or all of each disk drive’s
capacity.
It is possible to include the same disk drive in two different logical drives by using just a
portion of the space on the disk drive in each, as shown in the following figure.
Disk drive space that has been assigned to a logical drive is called a
segment
. A segment can
include all or just a portion of a disk drive’s space. A disk drive with one segment is part of one
logical drive, a disk drive with two segments is part of two logical drives, and so on. A segment
can be part of only one logical drive. When a logical drive is deleted, the segments that
comprised it revert to available space (or
free segments
).
A logical drive can include redundancy, depending on the RAID level assigned to it. (See
Selecting the Best RAID Level
on page 153
for more information.)
Once a logical drive has been created, you can change its RAID level or increase its capacity to
meet changing requirements. You can also protect your logical drives by assigning one or more
hot spares to them. (See
page 55
for more information.)
Three Disk Drives
(500 MB Each)
One RAID 5 Logical
Drive
One RAID 1
Logical Drive
250 MB
250 MB
250 MB
250 MB
250 MB
250 MB 250 MB
250 MB
250 MB
250 MB
Available
Space
Appears to Operating
System as one
250 MB disk drive
Appears to Operating
System as one
500 MB disk drive
