Gateway 840 VT-100, Руководство пользователя

Страница: 41 / 250

36
Chapter 3: Creating Disk Arrays
www.gateway.com
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.