IBM Hub/Switch, Руководство по установке

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Chapter 2 HPSS Planning
104 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
Guideline 4: Select the Stage on Open Background option if you want the stage to be queued
internally in the Bitfile Server and processed by a background BFS thread on a scheduled basis.
Explanation: The open request will return with success if the file is already staged. If the file needs
to be staged an internal staged request is placed in a queue and will be selected and processed by
the Bitfile Server in the background. A busy error is returned to the caller. This option allows a large
number of stages (up to 2000) to be queued in the bitfile server and processed as thread resources
are available. The other stage options will result in a busy error if thread resources are not
immediately available to process the request.
Guideline 5: Select the Retry Stage Failures from Secondary Copy option if you want to configure
a storage class so that stage failures to the primary copy can be automatically retried from a valid
second copy. The associated hierarchy must first be configured for multiple copies.
Explanation: When a stage fails form the primary copy, HPSS will examine the error, and for most
errors, it will examine the hierarchy for a valid second copy and reissue the stage from the second
copy. A typical usage would be to bypass a damaged tape. In this case, the tape may be locked out
via SSM and HPSS will recognize this and automatically go to a second copy if one exists. A
warning that this has happened will appear in the SSM Alarms and Events window.
2.9.3.4 Selecting Optimum Access Size
This field is only advisory in nature; however, for later releases it may be used by interfaces in
dynamically selecting good buffer sizes.
Guideline 1: Generally, if the file is being staged on open, Optimum Access Size should be set to
the same value as Optimum Access Size is set to in the storage class that is at the top of the
hierarchy.
Guideline 2: If data is not being staged to the top level before it is read (either automatically or by
user command), select a value that is an integral multiple of the largest Optimum Access Size field
found among the storage classes that make up this hierarchy.
Explanation: Attempting to set this field correctly will potentially ease conversion to later HPSS
releases.
2.9.3.5 Selecting Average Latency
This field can be used via the COS Hints mechanism to affect COS selection.
Guideline 1: This field should generally be set to the value of the Average Latency field in the
storage class that is at the top level in the hierarchy if data is being staged on open. If files are not
being accessed multiple times after they are staged, the average latency should be set to the latency
of the level they are being staged from.
Guideline 2: If most of the requests for files in this COS are read requests, then it may be best to set
the value of this field equal to the Average Latency field in the storage class in the hierarchy where
most of the data accesses will come from.
Guideline 3: If the predominant activity is write, use the Average Latency field from the storage
class at the top level in the hierarchy.