Chapter 2 HPSS PlanningHPSS Installation Guide September 2002 103Release 4.5, Revision 22.9.3.1 Selecting Minimum File SizeGuideline: This field can be used to indicate the smallest file that should be stored in this COS.Explanation: This limit is not enforced and is advisory in nature. If the COS Hints mechanism isused, minimum file size can be used as a criteria for selecting a COS. Currently, PFTP and FTPclients that support the alloc command will use the size hints when creating a new file. Ensure thatthe Minimum File Size and the Maximum File Size do not overlap; otherwise the data placementmay be indeterminate.2.9.3.2 Maximum File SizeGuideline: This field can be used to indicate the largest file that is to be stored in this COS.Explanation: If the Enforce Max File Size option is selected, an attempt to perform an operation ona file that would cause this value to be exceeded will be rejected. The underlying storage hierarchyshould be set up so that the defined storage classes support files of this size in a reasonable fashion.For details, see Sections 2.9.1 and 2.9.2 on storage class and storage hierarchies. This field can beused via the COS Hints mechanism to affect COS selection. PFTP and FTP clients that support thealloc command will use the size hints when creating a new file. Ensure that the Minimum File Sizeand the Maximum File Size do not overlap; otherwise the data placement may be indeterminate.2.9.3.3 Selecting Stage CodeThis field determines whether a file is to be staged to the highest level in the storage hierarchy whenthe file is opened. This field can be used via the COS Hints mechanism to affect COS selection. Thevalid options are as follows:Guideline 1: Select the No Stage option if file to be staged on open is not desired.Explanation: Data read from the file may come from lower levels in the storage hierarchy if the datadoes not already exist at the top level. This option is normally selected if the top level in thehierarchy is not disk or if the users of files in this COS wish to control staging directly via user stagerequests.Guideline 2: Select the Stage on Open option if it is desirable have the entire file staged to the toplevel in the hierarchy and to wait until this completes before the open call returns.Explanation: This would be a commonly selected option when the top level is disk and the files inthis class are small to moderate in size. Also, use this option if you want to be guaranteed that thefile is completely and successfully staged. If the stage fails, the open will return with an error.Guideline 3: Select the Stage on Open Async option if you wish to stage the entire file to the toplevel in the hierarchy and do not want the open to block.Explanation: When this option is selected, the file is staged up in increments and the read and writecalls that are accessing this file are blocked only until that portion of the file they wish to operateon has been completely staged. Normally, this option would be selected when the top level is diskand the files in this class are fairly large in size. This option is only available when the top level inthe hierarchy is disk. If the top level is tape and this option is specified, the No Stage option will beused instead.
