HP Surestore Disk Array 12h - And FC60 Service Manual page 102

Concepts and Management
Managing the Disk Array Capacity
Some General Rules Regarding Capacity Allocation
Building on the information provided in the preceding example, there are some general rules you can
follow to achieve the most efficient use of your disks capacity.
Using disks of all the same size in the array produces the most efficient use of capacity. In this case,
there is only one segment and only one parity block.
When adding a new disk, the array will be able to make almost the entire capacity of the disk available
to the host (assuming the disk is not larger than the other disks). This is because the Active Hot Spare
and parity requirements are already satisfied. For example, adding another 4.3-Gigabyte disk to the
array would yield almost 4.3 Gigabytes of additional capacity. A small amount would be required for
RAID 0/1 and controller overhead.
Adding one or two large disks to an array of smaller disks will not yield the capacity you might expect.
The upper segment created by the new larger disks will be used for Active Hot Spare and parity, and
not for available capacity. For this reason, it is much better to have twelve 4.3-Gigabyte disks than six
9.1-Gigabyte disks.
When installing a 36-Gigabyte disk drive module into an HP SureStore E Disk Array 12H, the
controller firmware of the disk array must be at revision HP54 or higher. The use of 36-Gigabyte disk
drives on controller firmware revision previous to HP54 is not supported. If a 36-Gigabyte disk drive
is manually included under older controller firmware, it will be treated as if its physical capacity is
about 24 Gigabytes.
AutoRAID Capacity Planning Tool
For planning the maximum usable capacity that can be achieved, refer to the AutoRAID Capacity Planning
Tool on the World Wide Web as follows:
On the World Wide Web:
http://www.hp.com/go/autoraid_tool
http://www.hp.com/essd/model12H_autoraid_tool.html
http://www.hp.com/essd/capacity.html
Inside the HP firewall (HP-qualified personnel only):
http://essd.boi.hp.com/products/DiskArrays/autoraid/capacityplanningtool/index.htm
http://essd.boi.hp.com/products/DiskArrays/autoraid/capacityplanningtool/capacity.html
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