US Robotics 7931 Betriebsanweisung PDF herunterladen (Seite 169)

Chapter 5 Staging 145

CODE EXAMPLE 5-4 shows an example preview.cmd file that addresses these three

conditions.

For environments in which user access to data is of paramount importance, the VSN

drives are limited, or file archival is performed as a background function, you can

use the preview.cmd file to influence how the storage system resources service the

staging requests. You can customize the settings in the preview.cmd file to support

any of the preceding scenarios and influence the configured Sun StorageTek SAM

environment.

Because data is not affected by the settings in this file, you are encouraged to

experiment and adjust the directive settings to achieve the proper balance between

archiving and staging requests when weighed against the priorities of each preview

request.

Example 1: Enforcing Stage Requests

The following example calculations show how you can use a negative value for

wm_priority to ensure that stage requests have priority over archive requests. This

example assumes the following:

■ Several requests are sitting in the queue for 100 seconds.

■ The default value vsn_priority is 1000.

TABLE 5-7 shows how the total request priorities are calculated.

CODE EXAMPLE 5-4 Example preview.cmd File

# condition 1

lwm_priority = -200.0

lhwm_priority = -200.0

hlwm_priority = -200.0

# condition 2

hwm_priority = 500.0

# condition 3

age_priority = 1.0

TABLE 5-7 Request Priority Example

Priority Calculation

Archive VSN with priority, LWM: 1000 + (-200) + (1 x 100) = 900

Stage VSN with priority, LWM: 1000 + 0 + (1 x 100) = 1100

Stage VSN without priority, LWM: 0 + 0 + (1 x 100) = 100

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US Robotics 7931 Betriebsanweisung Seite 169