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Writer: Rickard Project: Compaq Smart Array 3200 Controller Reference Guide Comments: 340862-002
File Name: B-CH01.DOC Last Saved On: 12/7/98 8:24 AM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
Using the Array Accelerator
The Smart Array 3200 Controller 64-MB array accelerator provides 56-MB
read/write cache, that improves data access performance to the drive array with
the accelerator acting as a posted-write cache and as a read-ahead cache. The
write cache can accept data from the server at a very high speed. At the same
time, read and write caches can be accommodated by the drivers. The read-
ahead cache uses a multi-threaded algorithm to predict the next likely read
operation for the array. This data is then read into the array accelerator from the
drives. When the Smart Array 3200 Controller receives a read request for the
cached data, the data can be brought into the system at memory speeds and
avoid the latency of a disk access. The array accelerator feature can be disabled
manually with software or by the Automatic Performance Tuning Feature.
NOTE: The Smart Array 3200 Controller is not operable without the array
accelerator board attached.
The array accelerator’s ECC memory provides a high level of data integrity.
ECC memory detects and corrects hard and soft memory errors without
affecting performance.
The array accelerator is backed up with onboard rechargeable batteries so that
the data temporarily held (cached) there is safe during equipment failure or
power outages. This is particularly important for data that has been cached by a
posted-write, but has not yet been written to the hard drives. The batteries
preserve data in the array accelerator for up to four days.
IMPORTANT: The rechargeable batteries on a new Smart Array 3200
Controller may be discharged when the board is first installed. During server
power-up with discharged array accelerator batteries, Power-On Self-Test
(POST) displays the code “1794,” indicating that the array accelerator is
disabled. This does not require action on your part. The array accelerator is
enabled automatically when the batteries are charged to 90 percent of their
capacity.
It can take up to 36 hours for the internal circuitry to fully charge the
batteries . During this time, the array accelerator will be disabled; the Smart
Array 3200 Controller will function properly, but without the performance
advantage of the array accelerator.