# Understanding adaptive read-ahead cache mode

The ServeRAID controller continually reevaluates whether to transfer data from disk to its local cache in increments equal to the stripe-unit size or in increments equal to the system I/O request size.

The ServeRAID-4 controllers and the ServeRAID-3HB controller come with the adaptive read-ahead mode as a standard feature. The ServeRAID-3H and ServeRAID-3L controllers must use new ServeRAID firmware (version 3.50, or later) to implement adaptive read-ahead cache mode. You can download and install the new firmware for the ServeRAID-3H and ServeRAID-3L controllers.

If you have the controller and firmware for adaptive read-ahead mode installed, the ServeRAID Manager reports Adaptive on the controller information pane. Otherwise, the information pane states either Enabled or Disabled.

Note: With this new firmware, the non-Adaptive read-ahead modes are no longer available in the ServeRAID Manager. You can override Adaptive read-ahead, but not through the ServeRAID Manager. Instead, use the IPSSEND command-line program. This program comes with the device option and is on the IBM ServeRAID Support CD. For more information, refer to the IBM ServeRAID-4 Ultra160 SCSI Controller User's Reference.

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