HP StorageWorks 500 G2 Modular Smart Array - Manual (Page 70)

70 HP StorageWorks MSA500 G2 Storage System User Guide
Accelerator ratio
The MSA500 G2 controller has an onboard cache called an Array Accelerator,
which performs both write-posting and read-ahead caching. The setting in
CPQONLIN determines the amount of memory allocated to the read and write
caches.
For example, if the Accelerator Ratio is set to Read 75%:Write 25%, 75% of
Array Accelerator cache is dedicated to read-ahead cache and 25% is dedicated
to the write-posting cache. This option can be modified from the Controller
Settings menu.
Expanding an array
During an expand, performance may be slightly degraded. In most cases,
however, any potential degradation is offset by the addition of physical drives.
Some tips for expanding include:
• Perform the expand process during periods of low server use. If you must
expand during peak periods, CPQONLIN enables you to set the priority of
the expand. Setting the priority to LOW affects performance the least, but it
takes longer for the new space to become available.
• When expanding, always add drives with a capacity equal to or greater than
the capacity of the smallest drive in the array. Adding larger drives wastes
space because only the space that is equal to the smallest drive size can be
used.
Adding or configuring spare drives
When adding a spare drive to an array, an unassigned drive must exist or a drive
already assigned as a spare must exist on another array. You can assign a single
spare to any number of arrays or assign separate spares.
When you select Assign Spare Drive, only drives that qualify appear (for
example, only those spares that are large enough appear). If drives that you
expect to see do not appear, switch to the physical drive view (Tab key), and
check the size of the drives. The capacity of the spare must be equal to or greater
than the capacity of the smallest drive in the array.