Compaq RAID Array 4100 User Manual page 104

Accelerator Ratio
The RA4000 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%,
then 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 when the Array Accelerator is installed.
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 are:
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Perform the expand process during periods of low server use. If you
must expand during peak periods, the Array Configuration Utility for
NetWare allows you to set the priority of the expand. Setting the priority
to LOW will affect performance the least, but it will take longer for the
new space to become available.
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When expanding, you must add drives of at least the same capacity as
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, there must be an unassigned drive or a
drive already assigned as a spare 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 will appear (for example, only
those spares that are large enough will 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 spare must be as large as the smallest drive in the array.
Online RAID and Stripe Migration
Using CPQONLIN, you can modify both the RAID level and Stripe Size of an
existing logical drive while online. To migrate a drive, select the drive setting
option under the logical drive menu for the drive you wish to modify. Select
the new RAID level and/or stripe size from the choices presented to you. If the
new settings are valid, the migration will begin when you save your changes.
Running the Array Configuration Utility 5-31