_______________________________________________________________ STACKER NOTE STACKER NOTE Title: STACKER DRIVE SPACE REPORTING (Applies to Stacker for Windows & DOS 2.x & 3.x) STAC FAX 31603 (6/93) _______________________________________________________________ BACKGROUND Stacker 2.0's SCHECK or Stacker 3.0 & 3.1's CHECK /D show exactly how the space has been used in the Stacker drive. Here is an example of an SCHECK & CHECK /D report: Volume in drive C is STACVOL_DSK No errors found Stacker Drive Statistics: Stacker Drive STACVOL File Drive C: D:\STACVOL.DSK ------------------ ----------------- Total Bytes: 147,095,552 73,550,336 Bytes Used: 60,334,080 (41.0%) 33,004,032 (44.9%) Bytes Free: 86,761,472 (59.0%) 40,546,304 (55.1%) Bytes per Cluster 8,192 2,048 Stacker Drive Compression Ratio = 1.8:1 Projected Bytes Free = 74,096,640 Fragmentation Level = 0% Note: Not all the lines will be displayed if Stacker version 2.x SCHECK utility is used. What does it all mean? The Left Column: This column contains information about your "logical" drive's data. The figures are "based on an anticipated compression ratio of 2.0:1." In this example, your compressed drive (Total Bytes) has been established at approximately 147 MB. There are approximately 60 MB used with enough clusters left on the compressed drive to accommodate approximately 86 MB of additional data. Utility programs which have the capability of reporting available disk space could report either "Bytes Free" or "Projected Bytes Free." _______________________________________________________________ Copyright 1993, Stac Electronics Page 1 of 3 The Right Column: This column shows the usage of actual "physical" hard disk space inside the STACVOL.DSK file. The Stacvol file contains all of the data and free space for the Stacker drive C. Its name and location are shown in the column header. In our example, D:\STACVOL.DSK is about 73 MB in size and has used only 33,004,032 bytes of storage space. Therefore, there are 40,546,304 bytes of physical free space left in D:\STACVOL.DSK. Compression ratio The Stacker drive compression ratio indicates the average compression of all the files in that drive. The compressibility of the files is generally dependent on their contents. In the above example, the 1.8:1 ratio is slightly less than a 2.0:1 ratio you typically get for an average mixture of files. This tells us that the files in this Stacker drive are taking up slightly more space than if the compression rtio was 2.0:1. A drive full of graphics files may achieve an average compression of 8.0:1 or more. An 8.0:1 ratio would mean that the files are taking up 1/8 the space they would on a standard drive. Conversely, some files are already compressed, such as "zipped" files. Stacker will attempt to compress these files even more however, since these files have already been previously compressed, little or no additional compression occurs. Previously compressed files will actually lower the average compression ratio for the compressed drive in which they reside. If you used a third party utility to "zip" the files, you could improve your average compression ratio by either storing these files on an uncompressed drive/diskette or by "unzipping" the files and let Stacker compress them. Note The drive compression ratio does not display if the drive is empty. Projected bytes free This number is Stacker's "estimate" of the available space left on the Stacker drive. It is determined by one of the following methods: Method 1. By multiplying the physical bytes free (right side) by the compression ratio if it is less than 2.0:1. The example shows the compression ratio rounded off to tenths. The actual compression ratio used in the calculation is not rounded off. ------------------------------------------------------------- Copyright 1993, Stac Electronics Page 2 of 3 Method 2. The logical bytes free (left side) if your compression ratio is 2.0:1 or greater. The projected bytes free is limited to the smaller of these values. In our example, physical bytes free multiplied by the compression ratio would be 74,096,640. However, there are enough unallocated clusters to accommodate the 86,761,472 bytes free from the left side column (based on an anticipated compression ratio of 2.0:1). The Projected Bytes Free become the smaller of these two values. Note When the number for physical bytes free goes to zero, the drive is full. You cannot "grow" the drive to create more physical space. Also, if the drive is less than 12% full, the projected bytes free will equal the "logical" bytes free number (left column). Expected Compression Ratio If your average compression ratio significantly varies from your original compression ratio (default is 2.0:1 unless modified) established when you installed Stacker, you can either increase the number of allocation units or decrease them. You would do this by either adjusting the "Expected Compression Ratio" from the Stacker Toolbox in version 3.x or by using "Grow & Shrink" from the Stac Command Assistant in version 2.x of Stacker. You can only adjust the expected compression ratio within a range that is either twice or half the original value established at installation time (normally 2.0:1 unless you originally set it at another value). By adjusting the Expected Compression Ratio (GROW operation in version 2.x) you can adjust the figures being reported in the left column to improve the accuracy of available space. Since your average compression ratio can fluctuate as you add, modify or delete files from your drive, modifying the expected compression ratio should only be done if there is a "significant deviation" from the original compression ratio (normally 2.0:1) established when you installed Stacker. _______________________________________________________________ Copyright 1993, Stac Electronics Page 3 of 3