HP Surestore Disk Array 12h - And FC60 Service Manual page 96

Concepts and Management
Disk Array Hardware
Using Disks of Different Capacities
Disks of different capacities can be installed in the same array, providing maximum flexibility and
expandability for your disk array. This makes it easy to increase your array's data capacity as new, higher-
capacity disks become available.
There is an important point to remember when using disks of different capacities in the same array: You
should add at least two high-capacity disks to the array to use their entire capacity. If you add a single high-
capacity disk, the array will not be able to use its full capacity. In this situation, the array can only use
capacity equal to that of the largest disk already installed in the array. For example, if your disk array has
only 4.3-Gigabyte disks and you add a single 9.1-Gigabyte disk, the array can only use 4.3 Gigabytes of the
high-capacity disk (at least until another 9.1-Gigabyte disk is added).
Figure 22. Using Disks of Different Capacities
This is a result of the way in which redundant data is stored using RAID technology. Because there is no
corresponding space on another disk for redundant data, the array cannot use the upper portion of the high-
capacity disk. Thus, adding a single high-capacity disk will not yield all the additional capacity you had
expected. To avoid this situation, always install at least two high capacity disks in the array.
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