Chapter 2 HPSS Planning130 September 2002 HPSS Installation GuideRelease 4.5, Revision 2volume to use in allocating this disk space. An integer value from 1 to 10 can be entered. Forexample, if four AIX logical volumes are allocated to SFS, use values from 1 to 4 to assign eachmetadata file to the appropriate volume. The Space Allocation Per Encina Volume table, located on thesame worksheet, will use this allocation to calculate total disk space requirements per SFS volume.By varying the SFS volume number, the administrator can experiment with how to best allocate themetadata files based on the logical volume sizes.It is important to note that calculating the size of an SFS balanced-tree file is not easy and issometimes inaccurate. The file sizes do not grow linearly according to the number of recordsbecause of the changing height of the B-tree and the fact that leaf pages may not be full. In thisspreadsheet, the maximum height of the B-tree is calculated based on the order of the B-tree andthe number of records. In other words, the spreadsheet assumes a worst case, which is appropriatewhen planning disk space requirements.For more information on how the size of SFS B-trees can be calculated, refer to Encina Overview, anIBM ITSO Redbook (GG24-2512-00).Secondary Index 1—This section shows the disk space requirement for the first secondary indexassociated with each metadata file, if such an index is used. The SFS Vol # column allows this diskspace to be allocated to a particular logical SFS volume. However, the managesfs utility used tocreate HPSS metadata files currently creates the file and all associated indices on the same SFSvolume. So normally, the SFS volume columns in the spreadsheet will contain the same logical SFSvolume number for a given metadata file row.If, for performance or disk-space limitation reasons, a secondary index is to be created on a differentSFS volume from the primary index, use managesfs to first create the metadata file specifying theSFS volume desired for the primary data/index, manually delete the secondary index using thesfsadmin command, and attempt to recreate the metadata file using managesfs while specifyingthe SFS volume desired for the secondary index. The second attempt to create the metadata file willyield an error indicating that the metadata file already exists; however, it will go ahead and recreatethe secondary index on the different SFS volume.Secondary Index 2—This section shows the disk space requirement for the second secondary indexassociated with each metadata file, if such an index is used.Secondary Index 3—This section shows the disk space requirement for the third secondary indexassociated with each metadata file, if such an index is used.Total Size (MBs)—This column calculates, in megabytes, the sum of all disk space used for theprimary data and index, as well as all secondary indices.Space Allocation Per Encina Volume—Continuing to the right on this worksheet, is another table thatsummarizes the disk space allocation per logical SFS volume per metadata file. These calculationsare based on the SFS Vol numbers entered in the previous table. At the bottom of this table are theoverall totals for each SFS volume, in megabytes.2.10.2.22 Encina SFS Disk SpaceThis section explains the disk space requirements of Encina, parts of which come from completingthe metadata sizing spreadsheet. The disk space used by Encina SFS falls into the followingcategories:
