Adaptec 5405 User Guide - Page 59
Understanding Logical Drives, Selecting the Best RAID Level
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Chapter 6: Modifying Your Direct Attached Storage ● 59 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. One RAID 1 Logical Drive Three Disk Drives (500 MB Each) 250 MB 250 MB One RAID 5 Logical Drive 250 MB 250 MB Available 250 MB Space 250 MB 250 MB 250 MB 250 MB 250 MB Appears to Operating System as one 250 MB disk drive Appears to Operating System as one 500 MB disk drive 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 152 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 54 for more information.)