Chapter 2 HPSS Planning104 September 2002 HPSS Installation GuideRelease 4.5, Revision 2Guideline 4: Select the Stage on Open Background option if you want the stage to be queuedinternally 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 needsto be staged an internal staged request is placed in a queue and will be selected and processed bythe Bitfile Server in the background. A busy error is returned to the caller. This option allows a largenumber of stages (up to 2000) to be queued in the bitfile server and processed as thread resourcesare available. The other stage options will result in a busy error if thread resources are notimmediately available to process the request.Guideline 5: Select the Retry Stage Failures from Secondary Copy option if you want to configurea storage class so that stage failures to the primary copy can be automatically retried from a validsecond 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 mosterrors, it will examine the hierarchy for a valid second copy and reissue the stage from the secondcopy. A typical usage would be to bypass a damaged tape. In this case, the tape may be locked outvia SSM and HPSS will recognize this and automatically go to a second copy if one exists. Awarning that this has happened will appear in the SSM Alarms and Events window.2.9.3.4 Selecting Optimum Access SizeThis field is only advisory in nature; however, for later releases it may be used by interfaces indynamically selecting good buffer sizes.Guideline 1: Generally, if the file is being staged on open, Optimum Access Size should be set tothe same value as Optimum Access Size is set to in the storage class that is at the top of thehierarchy.Guideline 2: If data is not being staged to the top level before it is read (either automatically or byuser command), select a value that is an integral multiple of the largest Optimum Access Size fieldfound among the storage classes that make up this hierarchy.Explanation: Attempting to set this field correctly will potentially ease conversion to later HPSSreleases.2.9.3.5 Selecting Average LatencyThis 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 thestorage class that is at the top level in the hierarchy if data is being staged on open. If files are notbeing accessed multiple times after they are staged, the average latency should be set to the latencyof 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 setthe value of this field equal to the Average Latency field in the storage class in the hierarchy wheremost of the data accesses will come from.Guideline 3: If the predominant activity is write, use the Average Latency field from the storageclass at the top level in the hierarchy.
