HP StorageWorks 1500cs Modular Smart Array - Manual (Page 21)

Modifying an existing configuration 21
Controller settings
The default controller settings that ACU provides are adequate for many purposes. When necessary,
however, you can use the Controller Settings task to:
• Alter the priority that the system gives to an array expansion or rebuild
• Disable the array accelerator (if one is present)
• Change the ratio of read cache to write cache (if the controller has battery-backed cache)
To change the controller settings:
1. Click Controller Settings, and then click Begin.
The next two screens enable you to change the settings for the expand priority and the rebuild
priority. These settings determine how much importance you want an array expansion or rebuild to
have relative to normal I/O operations.
• With low priority, the expansion or rebuild takes place only when the array controller is not busy
handling normal I/O requests. This setting has minimal effect on normal I/O operations.
However, there is an increased risk that data will be lost if another physical drive fails while the
rebuild or expansion is in progress.
• With high priority, the rebuild or expansion occurs at the expense of normal I/O operations.
Although system performance is affected, this setting provides better data protection because the
array is vulnerable to additional drive failures for a shorter time.
• At the medium priority setting, expansion or rebuild occurs for half of the time, and normal I/O
requests are handled during the rest of the time.
2. Set the expand priority to high, medium, or low, and then click Next.
3. Set the rebuild priority, and then click Next.
If the controller has an array accelerator, a screen now appears that gives you the option of
disabling it for particular logical drives.
NOTE: Disabling the array accelerator for a logical drive reserves use of the accelerator cache for other
logical drives on the array. This feature is useful if you want the other logical drives to have the maximum
possible performance (for example, if the logical drives contain database information).
4. Select the logical drives for which the array accelerator should be disabled, and then click Next.
If the controller has a battery-backed cache, a screen now appears that enables you to change the
read/write cache ratio. This ratio determines the amount of memory allocated to read and write
operations. Different types of applications have different optimum ratios. You can change the ratio
only if the controller has a battery-backed cache (only battery-backed cache can be used for write
cache) and if there are logical drives configured on the controller.
5. Select the ratio that you want the controller to use, and then click Next.
6. Click Finish to accept the changes.
7. Click Save to apply the changes to the system, and then click OK on the confirmation alert.
Create an array
1. Click Create an array, and then click Begin.
2. Select the type of drive to be used in the array.
3. Select the physical drives that you want to use in the array.
• Use physical drives of comparable capacity.
ACU uses the same amount of space from each physical drive to build an array. Because this
amount cannot exceed the capacity of the smallest physical drive, the extra capacity of any
larger drive in the array is unusable.