HP 2000fc Hp StorageWorks 2000 Family Modular Smart Array CLI reference guide - Page 111

Cache Optimization Mode Before creating or modifying a volume, determine the appropriate cache optimization mode. The controller supports super-sequential optimization mode for sequential I/O and standard optimization mode for random I/O. The cache optimization mode setting for each volume optimizes the cache block size used by the controller: ■ For sequential optimization, the cache block size is 128 Kbyte. ■ For random optimization, the cache block size is 32 Kbyte. An appropriate cache block size improves performance when a particular application uses either large or small stripe sizes: ■ Video playback, multimedia post-production audio and video editing, and similar applications read and write large files in sequential order. ■ Transaction-based and database update applications read and write small files in random order. Since the cache block size works in conjunction with the default stripe size set by the cache optimization mode for each volume you create, these default stripe sizes are consistent with the cache block size setting. You can, however, specify a different stripe size for any volume at the time you create it. For more information, see "create volume" on page 68. Read-Ahead Size You can optimize a volume for sequential reads or streaming data by changing the amount of data read in advance after two back-to-back reads are made. Read ahead is triggered by two back-to-back accesses to consecutive logical block address (LBA) ranges. Read ahead can be forward (that is, increasing LBAs) or reverse (that is, decreasing LBAs). Increasing the read-ahead size can greatly improve performance for multiple sequential read streams. However, increasing read-ahead size will likely decrease random read performance. The default read-ahead size, which sets one chunk for the first access in a sequential read and one stripe for all subsequent accesses, works well for most users in most applications. The controllers treat volumes and mirrored virtual disks (RAID 1) internally as if they have a stripe size of 64 Kbyte, even though they are not striped. Chapter 3 Command Descriptions 111