HP StorageWorks MSA2012i HP StorageWorks 2000 Modular Smart Array Reference Gu - Page 89
Changing a Volume’s Read-Ahead Cache Settings
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3. Select the volume to rename. 4. In the Change Volume Name field, type a new name. The name is case sensitive and can include 20 characters, but not comma, quotation mark ("), or backslash. 5. Click Change Volume Name. When processing is complete, the new name is displayed in the Volume Menu panel. Changing a Volume's Read-Ahead Cache Settings As an Advanced Manage user, you can optimize a volume for sequential reads or streaming data by changing its read-ahead cache settings. The read-ahead cache settings enable you to change the amount of data read in advance after two back-toback 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 cache 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. Caution - Only change the read-ahead cache settings if you fully understand how the host operating system, application, and adapter move data so that you can adjust the settings accordingly. Be prepared to monitor system performance using the virtual disk statistics and adjust read-ahead size until you find the optimal size for your application. To change a volume's read-ahead cache settings: 1. Select Manage > Volume Management > Volume Menu > Read Ahead Cache. For each virtual disk, the virtual disk panel shows a status icon; the name, RAID level, size, number of disk drives, and number of volumes; and utility status, if any. 2. Select a virtual disk. The selected virtual disk's volume names, sizes, and read-ahead cache sizes are displayed, and the amount of free space. Chapter 3 Managing Storage 89
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