Hewlett-Packard 127695-B21 - Smart Array 431 RAID Controller Manual
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Brand: HP
Category: Adapter
Type: Technology brief
Model: HP 127695-B21 - Smart Array 431 RAID Controller , HP 128293-B21 - Integrated Smart Array Controller RAID
Pages: 9 (0.37 Mb)
Download HP 127695-B21 - Smart Array 431 RAID Controller Technology brief
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Smart Array Controller Technology: Drive Array Expansion and Extension
3
capacity
expansion
Capacity expansion is the process of adding physical drives to an array that
has already been configured. The logical drives (or volumes) that exist in the
array before the expansion takes place are unchanged. Only the amount of
free space in the array changes.
For example, suppose that an existing array consisted of four physical drives
and the administrator wants to expand the capacity to six physical drives. This
is like having four glasses full of water, and pouring that water from the original
four glasses into six glasses (see figure 1). The amount of water (the volume of
the logical drive) has not changed — it has merely been redistributed, or
expanded, into a larger number of containers (drives).
figure 1. Array capacity expansion redistributes an array into a larger number of
physical drives. The size of the logical drive does not change.
Thus, if an existing array is nearly filled with logical drives, an administrator can
add new physical drives and initiate a capacity expansion through ACU or
ACU-XE. The program automatically checks the drive hardware configuration.
Then, the existing logical drive is distributed across all physical drives in the
expanded array without affecting any existing data. If the array being
expanded contains more than one logical drive, data will be redistributed one
logical drive at a time.
The expansion process is entirely independent of the system OS. For example, if
a 10-gigabyte (GB) logical volume is expanded from four drives into six drives,
the OS is unaware of this change.
The amount of time it takes to perform an online capacity expansion depends
on several parameters: drive speed, the server microprocessor speed, the
amount of other I/O work the server is doing, and the priority level of the
capacity expansion. This priority level can be changed from low (the default in
ACU) to medium or high to expand the volumes as quickly as possible.
Depending on these factors, the expansion process takes somewhere
between 10 – 15 minutes per GB.