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1994-03-04
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NOVELL TECHNICAL INFORMATION DOCUMENT
TITLE: Stacker Statistics
DOCUMENT ID: 014920
DOCUMENT REVISION: A
DATE: 25FEB94
ALERT STATUS: Yellow
INFORMATION TYPE: Issue
README FOR: NA
NOVELL PRODUCT and VERSION:
Novell DOS 7
ABSTRACT:
This document explains the statistics shown on a Stacker
compressed partition under Novell DOS 7.
------------------------------------------------------------------
DISCLAIMER
THE ORIGIN OF THIS INFORMATION MAY BE INTERNAL OR EXTERNAL TO
NOVELL. NOVELL MAKES EVERY EFFORT WITHIN ITS MEANS TO VERIFY
THIS INFORMATION. HOWEVER, THE INFORMATION PROVIDED IN THIS
DOCUMENT IS FOR YOUR INFORMATION ONLY. NOVELL MAKES NO EXPLICIT
OR IMPLIED CLAIMS TO THE VALIDITY OF THIS INFORMATION.
------------------------------------------------------------------
ISSUE
This document is not designed to be an introduction to the
Stacker portion of Novell DOS 7. Users who are new to
Stacker should read the following references before reading
this document:
Novell DOS 7 User Guide: Chapter 12 "Disk Compression"
Novell DOS 7 README.TXT
Stacker section within the DOSBOOK online reference
manual
(Type DOSBOOK STACKER at the command line.)
Novell DOS 7 offers three utilities for examining statistics
on a Stacker drive: DIR, XDIR, and CHKDSK. Each of these
utilities is specifically written to understand the internal
structures of a Stacker drive. For a list and description
of switches for these utilities refer to DOSBOOK or type the
utility name followed by a /? (for example, DIR /?) at the
command line.
DIR
The Novell DOS 7 DIR command has been written to give an
accurate calculation of free space on a Stacker drive.
Please see the Estimated Bytes Free section below for a
description of how free space is calculated for a Stacker
drive.
XDIR
The Novell DOS 7 XDIR command has been written to give
compression ratios for each file on a compressed drive as
well as an average compression ratio for the current
directory. An example of an XDIR of the root directory
follows:
--a--- 355 8.0:1 2-24-94 9:32a c:autoexec.bat
--a--- 73 8.0:1 2-18-94 10:32a c:autostac.bat
------ 56,081 1.4:1 1-26-94 7:00a c:command.com
--a--- 306 8.0:1 2-23-94 11:43a c:config.sys
rs--h- 27,880 1.4:1 1-26-94 7:00a c:ibmbio.com
rs--h- 29,684 1.1:1 1-26-94 7:00a c:ibmdos.com
DIRECTORY 2-18-94 10:02a c:nwclient
DIRECTORY 2-18-94 10:02a c:nwcntl
DIRECTORY 2-18-94 10:02a c:nwdos
--a--- 4,768 8.0:1 1-26-94 7:00a c:nwdos.386
DIRECTORY 2-18-94 11:25a c:windows
DIRECTORY 2-18-94 2:02p c:wpc20
DIRECTORY 2-18-94 2:00p c:wpwin60
total files 7 total bytes 119,147 disk free space
39,997,440
average compression ratio 1.6:1
To get an average compression ratio for the entire drive,
use the command XDIR /S at the root of the Stacker drive to
include all subdirectories. The average compression ratio
figure obtained by doing an XDIR /S is representative of all
the files on the drive. This figure is calculated by
averaging the actual compression ratio for each file on the
drive. An example of the last two lines of an XDIR /S
follows:
total files 1,304 total bytes 58,252,054 disk free space
39,997,440
average compression ratio 1.6:1
In the example, the average compression ratio of 1.6:1 is
slightly below the expected compression ratio for the drive
(fixed at 2.0:1). This suggests that the files on the
Stacker drive are taking up slightly more room than
expected.
A Stacker drive is most efficient when the average
compression ratio is as close to the expected compression
ratio as possible. Ultimately the average compression ratio
should not be much higher or lower than the 2.0:1 expected
compression ratio.
If the average compression ratio is much lower than 2.0:1
(as an example 1.2:1), an overabundance of poorly
compressible data is on the drive. A user might consider
taking files that have a compression ratio (found with XDIR
/S) much lower than 2.0:1 off the drive.
If the Stacker Drive Compression Ratio is much higher than
2.0:1 (as an example 8.0:1), an overabundance of highly
compressible data is on the drive. A user might consider
taking files that have actual compression ratio (found with
XDIR /S) much higher than 2.0:1 off the drive.
Note: The expected compression ratio is set at 2.0:1.
Therefore, there are twice as many file allocation
units in the Stacker FAT.
A Stacked drive with files that compress at a higher ratio
will use the allocation units at the same rate as files that
compress at a lower ratio. Even though a drive may have a
very high Stacker Drive Compression Ratio, such as 8.0:1,
you will not be able to store any more data than the
expected compression ratio of 2.0:1 allows.
XDIR also gives accurate used and free space information on
a Stacker drive. Please see the Estimated Bytes Free
section below for a description of how free space is
calculated for a Stacker drive.
CHKDSK
The Novell DOS 7 CHKDSK command used with a /D parameter
will display space usage on a Stacker drive. An example
CHKDSK /D follows:
Volume STACVOL_DSK created Feb-18-1994 10:36
Checking cluster integrity...
Stacker Drive Statistics:
Stacker Drive STACVOL File
Drive C: D:\STACVOL.DSK
---------------------- --------------------
Total Bytes: 162,914,304 61,506,048
Bytes Used: 61,329,408 ( 37.6%) 37,220,864 ( 60.5%)
Bytes Free: 101,584,896 ( 62.4%) 24,285,184 ( 39.5%)
Bytes Per Cluster: 4,096 2,048
Fragmentation Level = 0
Checking FAT integrity...
162,914,304 bytes total disk space.
61,440 bytes in 2 hidden files.
114,688 bytes in 24 directories.
61,153,280 bytes in 1302 user files.
39,997,440 estimated bytes free.
4,096 bytes in allocation unit.
39,774 total allocation units on disk.
24,801 available allocation units on disk.
655,360 total bytes of memory.
621,216 total bytes of free memory.
620,240 bytes in largest free memory block.
Stacker Drive Drive C:
This column of CHKDSK /D reports information based on the
estimated compression ratio of all the files on the drive
being 1.6:1. These statistics represent logical disk space
as each figure represents how space on the Stacker drive
would be used if this were a standard DOS formatted drive.
In other words, this information is based on one cluster
being the smallest allocable unit on the drive. Consider
the method for reporting statistics in this column to be
equal to what CHKDSK would display on any normal DOS
formatted drive.
STACVOL File G:\STACVOL.DSK
This column of CHKDSK /D reports information based on actual
physical disk space used by Stacker. In other words, its
information is based on the amount of physical sectors (512
bytes) used within the STACVOL file after files have been
compressed.
Understanding that Stacker can store files at the sector
level is important. This is unlike a normal DOS formatted
drive, which stores files at the cluster level. Most
third-party utilities are incapable of reporting actual
physical disk space use on a Stacker drive.
Estimated Bytes Free
This number represents an estimate of the number of bytes
free on a Stacker drive. Actual usable space may vary based
on the compression ratio of the drive (see above note).
This estimate is based on the lesser of the two values found
using Method 1 and Method 2 that follow:
Method 1: Estimated Bytes Free is found by multiplying the
bytes free value in the STACVOL File column by the
average compression ratio (found with XDIR /S).
Although the average compression ratio is rounded
off to tenths, the compression ratio used in the
calculation is not rounded off.
Method 2: Estimated Bytes Free is equal to the bytes free in
the Stacker Drive column.
Note: SETUP will allow you to expand or shrink a Stacker
drive to increase or decrease the amount of space
on the drive. However, when the number of bytes
free in the STACVOL File column is zero, the drive
is full.
You cannot expand the drive to create more
physical space. Also, if the drive is less than
12 percent full, the estimated bytes free will
equal the bytes free value in the Stacker Drive
column.