Chapter 3: Creating Disk Arrays
Configuring array read-ahead and writeback cache
The following steps will guide you through configuring the read-ahead cache and writeback cache options for each array. Each array has a different set of cache settings. Read-ahead cache and writeback cache thresholds work together to allow fine tuning of the I/O performance. You will need to set these options for each array you have created.
Read-ahead cache
The Read-Ahead function improves the data retrieval performance by allowing the controller to read into cache a full stripe of data at one time, which greatly improves the cache hits. For smaller transfers the Read-Ahead algorithm can improve performance. If, for example, the stripe size is 256 KB (chunk size multiplied by the number of data drives) and the host requests 64 KB of data, when Read-Ahead is enabled, the controller will read in advance a full 256 KB. When the host request the next 64 KB block, the data will already be in the cache. Depending on the data patterns for your application, disabling the read-ahead cache can help load balance the read and write operations, which can increase performance.