Integrity Of Cached Data In The Array Accelerator; Configuring The Array Accelerator - Compaq 108164-003 - ProLiant - 800 White Paper

Configuration and Tuning of Sybase System 11 for NetWare on Compaq Servers Page 7

Integrity of cached data in the Array Accelerator

The Array Accelerator contains batteries that maintain any data in the cache if a system power
failure occurs. Make sure you maintain the batteries in a good condition and fully charged (they
are automatically recharged while system power is present). At a fully charged state, the
batteries can preserve data in the Array Accelerator for four days. When power is restored to
your system, an initialization feature writes the preserved data to the disk drives.
Another step to insure data integrity in case of system failure is to install an Uninterruptible
Power Supply (UPS). Installation of a UPS will allow the controller to flush all data out to disk in
the event of a power failure. The UPS does not, however, insure data integrity in the case of a
controller failure, when valid data exists in the Array Accelerator. In that case, the Array
Accelerator may be removed as a complete unit from one SMART-2 controller and installed on
another, while preserving any data cached. The data will be written to disk upon power up.

Configuring the Array Accelerator

The Array Accelerator of the SMART SCSI Array controller is configured via the Compaq
System Configuration Utility. The Array Accelerator of the SMART-2 Array controller is
configured via the Compaq Array Configuration Utility or the Compaq Array Configuration
Utility for NetWare. The changes made while running the Compaq Array Configuration Utility
for NetWare take effect immediately. In the following examples the Compaq Array
Configuration Utility is demonstrated. Always obtain the latest copy of the appropriate utility for
your Compaq SMART and SMART-2 Array controllers.
With the SMART Array controller, the Array Accelerator can either be enabled (100% write
cache) or disabled. This controller does not support read-ahead. The Array Accelerator can be
enabled or disabled on a per-logical-volume basis.
With the SMART-2 Array controller, you can select the ratio of read-ahead cache to write cache
for every controller. Once selected, this Array Accelerator ratio will apply to all logical volumes
on this controller that have the Array Accelerator enabled. You can enable or disable the Array
Accelerator on a per-logical-volume basis.
To select the Array Accelerator ratio for a SMART-2 Array controller, you must install and run
the Compaq Array Configuration Utility from diskettes or from the System Partition. Using the
Array Configuration Utility, highlight the appropriate controller and use the
"Controller/Settings..." option.
1996 Compaq Computer Corporation, All Rights Reserved Doc No 140A/0896